I have owned a 97 GMC K1500 with 5.7 for 25 years. I have rebuilt or replaced almost every component on this truck and we are still driving it today. The A/C has been problematic for a few years. I watched your video and noted that the control was the only component that was still original. I discovered yesterday a long time refrigerant leak was due to the low side Schrader valve leaking. After replacing it, the A/C once again blows 43 degree air but mainly out the lower vent and defroster. I see that the actuators are working but I suspect the air box door is not properly diverting the air to the center vents. Believe me, the removal of this dash is not easy! Having done it twice before, yesterday I found a quick, cheap solution: a $15 plug in fan I clipped to the dash by the lower vent. Man, does it blow that cold air from the vent up in my face! I know this is not the proper way to fix it, but it is an old truck and I have A/C again to face our Texas summer. This was an intriguing video, but unfortunately it was not a fix for mine. Keep up the good work. We RUclipsrs need good content like this!
I think the 4692 is an NPN transistor, at least it checks as one. I did a 95 truck today and it has 4 transistors. 4687,2857 were replaced with 2n4403. This fixed the issue. There are (2) 4692 near the potentiometers. I did not replace them, no need to tempt fate. The 2n4401 would be used there. I did another 95 a few years(7) back and used the mpsa56 and mpsa06 in the 4 spots. It works fine still. Fine Video, I sure wish I had it when I did the first one.
I have a 1996 C3500 6.5 Diesel with the same problem as yours. I will try this repair. Thank you so much for sharing this video. I would have never known how to fix this. Thank you
I did something I almost NEVER do, I replaced mine through Rock Auto with a "Standared Motor Parts" (when I was young, Standard supplied the highest quality points and condensers you could buy). They may be a China company now. But, they offered a 3 year warrenty as compared to OEM ACDelco of 90 days. It works perfect and was (I think around $150.00) and is well past 90 days. However, after seeing yet another astonishing RUclips of yours, I am going to get my original and see if I can fix it from what you have taught us all here. Amazing!
1999 GMC Yukon. All settings seemed to work fine until I installed car stereo. Somewhere during that time I smelled something burning. Stereo works great. Now no lights come on on the climate panel and air comes through vents for 1 second then automatically shifts up to dash defrost vents. Right knob does nothing now. Middle knob makes blend door actuator move as before, but no heat, though air comes out vents as powerful as before, and fan speed switch works fine on all levels. I'm going to do what you did, but only after buying a part. Then I'll have a spare part around in case this happens again. I assume there must be a short in the harness to the climate panel. Only a few inches of wire have become damaged somehow. I will re-assemble the dash before I re-attach negative battery cable to prevent wiggling the wires and possibly re-damaging the new panel. Thank you very kindly. BTW mine doesn't have the rear defrost button, I only have defrost on the mode switch. Does this mean the plugs in the back won't match up with a 3 button panel?
With age the chances for a harness short when fiddling in that radio area are far higher, as the wiring insulation brittles up. Rear defrost was a factory option, so not having it doesn't change the rest of the repair/connections advice. Just that you would have unconnected or uninstalled wiring because your truck wasn't built with that option originally is all. I believe I give the GM part numbers for all the panels in the video description, so that you can track down the same one, if you like.
Thanks for the video friend showed up on hottest day of the years Im in Phoenix 113 today her AC stopped working on her 96 suburban. I traced the problem to the control module after replacing the 50 amp AC fuse. I ordered a replacement AC delco module noticed it wasn't the the correct one she had rear defrost. After removing the old control module I noticed the problem the resister you said blows out was blown. I plugged in the replacement AC control mod I got on Amazon to see if the compressor would turn on well as soon as I pushed the AC button the transistor smoked in the new one. I crossed ref the numbers and they cross over to NTE159. Im headed to Frys electronics see if it will fix it but I suspect it will burn up again. The only thing I noticed was the AC relay might have been installed backwards didn't match the relay next to it that is under the hood in the fuse box with the 4 other relays and maxi fuses. The Transistor is 800ma PNP if it blows again i'm only out the $3
@blastman8888 when the transistor blows that fast it's a sure sign you have a short to ground in the circuit. That transistor supplies the +12VDC battery power to the circuit when activated and it exits the control module thru the light green wire on the passenger side flat connector into it. You can trace this light green wire coming out of the firewall into the engine bay, usually it starts with the pressure switch on the accumulator and then works its way over to the other other pressure switches and then the main computer. After a couple of decades like these trucks have you're going to have vibration/rub burns thru the wiring insulation somewhere causing the short. I'm going to presume you have a gasoline engine (diesel AC circuit is quite different) here's a couple of 1998 circuit diagrams that should help www.2carpros.com/images/question_images/204058/original.jpg and www.2carpros.com/images/question_images/204059/original.jpg . Just follow that light green wire out of the 'AC Switch' shown on the left of the first diagram and then thru the rest of the circuit until you find the short.
@@DrShock Thanks for the reply I will take a look at the wiring when I get a chance I removed the control module and AC relay I don't see any shorts with my meter to ground with and without both pressure switches jumper's inserted in the plugs at the relay plug. I was wondering if the Blend door air vent motor could be shorted and overloading that same green wire feeds that motor. After reading this www.silveradosierra.com/how-to-articles/how-to-repair-gmc-ck-series-trucks-hvac-control-unit-t77522.html he says the only propose of this transistor is shut off power to the control module when it see's 12V from the blower indicating the blower is shut off. This was designed to turn off the compressor when the blower was not running to keep it from icing over. He suggested jumper the transistor emitter to collector leads and add a relay to cut out the compressor. When you turn the blower on any speed the 12 V goes to 0v on the bias leg of that transistor though those resistors to make it switch 12 V on power the module up. It's a strange design not sure why GM would even bother with all that seems lot easier to just have knob shut off power to the control module when turn it to off.
This short I was talking about is going to be under the hood, not in the cab wiring. You have to trace and meter out the entire circuit across all three pressure sensors one at a time and to the PCM as well as to the left hand air flow blend door (not the temp blend one near the heater). What that guy is telling you in the article is not incorrect, but you're misunderstanding (I think) from his writeup that this transistor is making the connection for 12VDC to the ENTIRE AC CIRCUIT under the hood! That's what the little transistor does. If you have a short, following that article is not going to remove that situation and just leave you with then a burnt out fuse or worse - a burnt out PCM. I'd still strongly suggest the transistor blowing is a symptom of a short circuit here, just friendly advice. One you fix that sure, you could alternatively follow this guys advice to remove the weakness in the transistor design during normal workloads. But that short has to get fixed first.
@@Mike-01234 I am having the exact same problem as you (1996 Suburban K2500, 7.4L, Gas). I am on my third control module. Two used ebay ones and one brand new from Rock Auto. Each worked perfect and everything works but my "Max" A/C as that servo on the far right needs to be replaced and just "ticks" if activated so I never allow it to be powered. It is unrelated to the problem. It seems a random short just smokes the transistor. I tried using a DVOM to see if the light green wire at the flat connector would ground out. I could not shake it or move it and get it to ground out. I am thinking of just replacing it (light green wire) with a new wire full length and trying that. How are you doing and what have you done if you fixed yours? Thanks very much!
great video my problems exactly! Replaced climate control module 1 month ago! I went to the junk yard today pulled a control panel out of another suburban and put it in mine now everything works great again! pulled the brand new control panel out and it says made in china complete junk! bought the new one from Napa, so if you have this problem just find a working one from the junk yard! my new one from Napa only lasted one month before transistor failed! QUESTION can you switch control board from the old one that works to the failed one I got from Napa?
I have the same problem. Air blows out dash vents for 1 second when first turning key on, then I hear the actuators move, and no air from anywhere, but still can hear it blowing somewhere. Going to buy a new Dorman control module and hope it fixes the problem.
Preformed this fix on a cheap Chinese controller and it the AC started working again. Got the parts for like $5 at an electronics store. Working on replacing the relays in my transfer case control module and it should solve my 4x4 issues. I replaced the capacitor on the board and only one relay would fire. It puts it into 4x4 but won't take it out.
@@barryhaire7424 It's usually burning the transistor out due to a short somewhere in the harness. I've seen these where it's just a rub thru somewhere along the harness and it's intermittent when it will touch the engine and create that short to ground that kills these little transistors. Sometimes it can be from a momentary power spike though, in which case a replacement will be enough. Hard to say over an internet comment forum, every situation is unique.
@@DrShock ok thanks I have a 1996 sonoma that the ac is doing just like In the vid but I don't have the tools or skills to do what u did so I was wondering if it would be a waste of money to buy a new module
@@barryhaire7424 In your situation, then I might be more inclined to try a salvage yard pull first to inexpensively see what happens before spending on a new one. You'll of course want to pick a truck that was in an accident vs one sold off from being inoperative, to increase the probability its AC was still working.
Where do you recommend getting those little transistors?? Subscribed! Btw, one of my rear defoggers on my Dutch doors stopped working. What all could I do to diagnose the cause?
There's a link in the description for them. On the defogger, each door has it's own grid when you don't have the liftgate option. When you have the liftgate, which I presume is what you mean by dutch being it's a top half lift up glass door, there's only one grid. What usually goes wrong is you get a break in the brown wire grid that sticks onto the inside glass. But it can also be the door contact switches. If I had this problem I'd do a visual inspection of the grid, and check the fuse and relay for the defogger circuit. If those looked good I'd check the door contact switch assembly. Tools wise a voltmeter and test light along with a copy of the schematic to get started. You can find that schematic in the PDF of the service manual here - www.gmt400.com/threads/88-95-service-manuals.43575/
Great video! Bummer that your new selector console had a bad transistor though. Where did you find the new selector console? ANd how much? I just bought a console on eBay and it is in worse shape than mine, and plugged it in to find the same issue still occurring with the blower stuck on floor only, which led me to you. Still watching this now, haven't tried yet. Interestingly I had just replaced my blower motor prior to this selector switch going out.
So the replacement control module did not have a bad transistor, there was a short in the underhood engine AC wiring that was burning them out which is a common cause for this after a couple of decades of vibration the harness insulation wears thru in some spots. That particular short can be difficult to trace down, as often it only shorts on certain driving conditions (like over railroad tracks). I recommend only buying brand new, never used, on this part due to the way the plastic degrades with age the mounting tabs *will* yellow and break off. eBay can be an inexpensive source of new old stock parts, or rockauto.com for brand spanking new.
@@DrShock so are saying that you replaced the transistor on the new module in video right? And then said it worked at end of video? But then after driving a bit, burnt out again? @DrShock @DrShock when I was looking at my wiring, following from condenser and firewall etc. It is all wrapped up well and covered with the plastic tubing. So I cant really imagine that has happened here, but it's possible. I dont think it's the actuators, because none of them move at all when turning zone selector. The door flap for floor moves freely by hand. All the fuses look good, wires look good, ground locations look good. Connectors look clean. Think I just bought a used console with same issue baked into it? I do remember around the same time this went out that my radio must have shorted out or something because the music went from all the speakers playing to just the rear for a few seconds, and then the music came back to all speakers. I think that since my clips are broken on my selector console, and it has this open/expossd circuit board, that it bounced and touched the metal radio casing. That's about all I can see that would do it. I wonder if i should attempt to replace my transistor or not? Quite a coincidence that the used one i just bought has same exact issue.... i don't like that, makes me think something else is going on but I guess trial and error is the way to find it.
In my case I had the AC control module go out that was an ACDelco installed new and around 10 years old. The brand new ACDelco replacement died after a week which made me think at the time it was poor quality transistors. That prompted me to research the problem, trace down to this transistor and replace it and do this video. Later on I worked on this same problem on a different truck, and knowing this now I was able to trace the problem to a worn spot on the harness to the compressor creating a short in the circuit that this transistor feeds power into. So now I tend to suspect shorts as the cause for these transistors burning out every time. There's a few very specific symptoms of this particular problem I summarize in the description. If you don't have those, or have other things going on like the radio behavior, it could be you have multiple electrical problems going on.
@@DrShock well that story about your new replacement selector module and replacing the transistor doesnt really make sense to me, because where is your truck wiring shorting out then? You didn't find a short on your wires, but you did replace a bad transistor right? And dont you find it funny that a short is always blowing this same transistor, and resulting in the same single zone indicator knob dysfunction?And the short occurring with same exact wire?? Rather than wrecking the other components of the module? Funny it's always the zone selector gone bad, but all the rest works fine. It would be pretty rare for that one single wire, wrapped up and clustered with all of the rest of the wires, about 8 of them, to be the one single wire shorting everytime, and just that one single wire, none of the others. That radio thing I described happened one time, and is working fine ever since, it lasted about 5 seconds that's what I think may have touched the module with the metal radio case because the clips on module were broken allowing it to bounce up and touch radio. But I dont know for sure, just hypothesis. Otherwise I cant figure out why my zone selector went out on me, dont see any wiring issues, no shorts, or exposed wires. And my symptoms are the exact same thing that you have described, just the zone selector stuck blowing on floor in my original module, as well as the used one I just bought on Ebay, which also has broken mounting clips incidentally, but I didn't touch metal radio with circuit board myself on that one. So I guess my question is after you replaced your transistor on the replacement module, have you had the issue come up again on your truck? If not, does not really indicate a short circuit on your truck does it? And are you saying that you replaced a perfectly good transistor on your replacement module? I dont understand here, why didn't you repair the original one? I get that the other truck you worked on may have had a wiring short, but it seems this is a very common issue with these climate selector modules judging by the views and comments on the video. So idk, I think you were probably correct initially that these transistors will go out on that one zone selector only. Please let me know what you think, I appreciate the input and the attention to this matter. I am sort of racking my brain here and spent all day monkeying with these damn modules, looking over wires, looking over door actuators, fuses. The fact this other used module I bought has the exact same symptoms right off the bat upon plugging in, kind of detracts from your wiring short theory as well I believe.
Alot of questions here. I'll try and touch on them. You would use a transistor tester, a function on most high end digital multi-meters, to test the semiconductor before making a determination it's defective. So yes, it's straightforward to confirm the diagnosis with the right tools. Consulting the electrical schematic of the service manual, you'll find several flavors depending on the engine and fuel type. In all cases this particular power transistor feeds the power to the cycling switch first as it enters the engine bay from the dash. It's a green colored wire in the harness. The power feed then takes different wiring harness paths, and sometimes thru pressure switches too, for each engine type differently on its way to the AC compressor. The other transistors in the control module serve other purposes, some control the blend door signals, for example. So they wouldn't have anything to do with the power feed. In my experience transistors are fairly robust, what kills them is sinking alot of current quickly (a short), or overwhelming them with a rapid power surge (static electricity discharge for example). I've done this repair on several trucks now, and where I had the case of the transistor blowing out _every time_ it's *always* a short in the harness. Where you don't then it's more likely just that transistors day to die and nothing more to it. The only way to find out is remove the transistor, test it, and if bad replace it and see what unfolds from there.
I have a brand new unit in my truck already. The problem I have is that it blows air wherever it feels like. It doesn't matter where I set it. Floor, defrost, or vents I sometimes get vents sometimes defrost, sometimes floor, but most the time all of them. It's okay in the summer when it's just the A/C, but in the winter in ND it's not so good when you need as much heat on the windshield as possible. Have you ever run into this or heard of this?
If the vent and AC controls work (AC compressor turns on as expected, just outside air flow when expected) and the temperature blend works (ratio of cool to heat is as set) and the fan speeds are all working as expected, that would leave just the actuator motor for the zones. On these trucks it's to the right of the accelerator pedal and controls the flap/door that directs the air. If all the above are true, that would only leave that motor, or the flap itself, to check out.
OK. Now my New "Standard" one failed exactly as my ACDelco. Small puff of smoke out the right side of the control until then the exact symptoms you describe. I examined both ACDelco and Standard and failure was the same. So it appears I have an intermittent short. Could you please dumb it down and explain how I find this short that has now blown that transistor on both the original ACDelco and the new replacement? Again, both assemblies failed the same with the same symptoms you described in failure. 1996 GMC K2500. Thank You!
When they go intermittently like that, in my experience its a place where the harness has rubbed thru the insulation and is making contact to the engine ground somewhere intermittently. Very unlikely to be behind the dash, more likely under the hood so start there. If you go thru some of the older comments on this video, there's a thread with a PDF link to the GM service manual posted 6 months back where you can find the wiring schematic. This can help you follow the harness colors under the hood searching for any physical damage in the spots where it comes in contact anywhere metal. The damage can be very small! So a magnifying glass might be helpful. You're looking for bare copper showing no matter how small. The fix can be simply electrical tape short term, but longer term to wrap in some tough plastic piece to deal with the rubbing.
Also I should mention to check the refrigerant pressure switches for damage / shorting at their connectors (but do not remove them) as you follow the green colored wire in the schematic around to the compressor.
@@DrShock Thanks again. I must be missing something. I read all the posts and looked at the two views of the wonderful color schematic. All I can see is the light green wire going directly from the A/C Control module to the A/C high pressure cut out switch. From there to the CPU. I see no other routes as others have referred to. It seems like the easy thing is to just splice in a new (equal or better gauge) light green wire from the harness connector at the A/C Control Module to the HP Switch and then a new wire from switch to CPU. What am I missing?? Another thought: What about the ground wire going through the same harness at the A/C Control Module to gound up under the dash?? Couldn't a bad ground cause an over-current situation (I'm a mechanical guy not an electrical guy)?? It would be easy to splice an auxiliary ground from the existing black wire to some easy place under the instrument panel or behind the A/C Control module. I would greatly appreciate your more experienced and knowledgeable thoughts on this. I'm getting frustrated and am spending too much money on A/C Modules. I did order the transistors you recommended and will be trying to repair two modules that I have blown.
The wiring can vary with every engine even in the same model year for the AC. The 6.5L diesel V8 has the most connections with this particular light green wire circuit. Looking at the 5.7L Vortec V8 (page 6-1675 in the service manual) yes its just the high pressure cutout for that engine as well as the 5.0L V8. The 7.4L V8 schematic is on page 6-2789. That light green wire is directly connected from the transitor on the control module logic board to the high pressure cutout switch and then to the VCM/PCM pin C3 on all the gasoline V8s. If you see no insulation damage under the hood, I would check from the firewall back inside to the control module harness connector itself then. It would not be the ground shorting out the transistor, what's burning it up is sinking too much current. Ground problems would leave you intermittent or no function at all. I would also try disconnecting both the control module harness and the PCM/VCM connector C (both ends). And then seeing if you are getting continuity to ground on the light green wire from either end, highlighting a short to ground (do this test with a helper to wiggle around the wire harness during the test as well at both ends). If so, I'd then disconnect the high pressure switch connection and try again (to see if it is the switch that is shorting in some way internally). If its not the switch then you would still have a short somewhere, perhaps more likely on this engine from the switch to the VCM/PCM than the other part of the circuit. These can be very difficult and aggravating problems. Definitely one of those walk away for a bit and retry ones.
@@DrShock Great advice. I have 7.4 Gas so it is direct. I think the easiest thing is to just run my own wire from the A/C Module to the HP Switch and then from the Switch to the PCM. (From my experience it would be highly unusual for the switch to short to ground, but who knows!) It will take less time than a propper diagnostic as I have to work alone. My transistors arrived today so will take one A/C Module with replaced transistor, and then replace light green wire & green with white wire (I think) from switch to PCM and just see if it blows the transistor again. I will update this posting after I try that. Thank you again for all the valuable lessons and advice.
I ordered all new plugs for the three pressure switches. They all seemed loose and stretched out. We had problems with others before on the engine. I still feel though we have a wire directly touching some metal somewhere.
I have the 1996 GMC Yukon 2 door 4x4. It does NOT have AC or a redefroster. The Climate Control Module temperature knob is broken off. No I do not have the knob any longer. The PART is no longer supported by GM. I am looking to replace the entire module as the knob seats on a stem which is what is broken. Any leads are helpful
Your best bet on a part like this is a you pull it salvage yard. Like an LKQ PYP (Pull Your Part) or similar. AC delete would have been a fairly rare build for the late 1990s. Another option is to have your local GM dealer dig up the part number for the heater only control assembly, and put out some eBay and the like searches for an NOS one. Likely will take a very long time to get a hit though.
When you say resistor did you mean to say transistor given this video? Or are you talking about an actual resistor elsewhere on this same control unit circuit board? For the transistor the answer would be no, has nothing to do with the blower motor circuit. In my experience the only shorts that blow this transistor are either on the control unit, over voltage on the incoming power harness, or a short to ground on the outgoing power harness (the green wire on the flat connector heading into the accumulator cycling switch first and then onwards).
@@DrShock yes I ment transistor I put a new control panel in and within 30 seconds it fired the transistor and went back to not working i guess I'll retrace the green wire once more
I replaced the transistors, but one is still blowing our after replacement. I understand that there may be a short from the control unit harness to the high pressure cutoff switch on the back of the AC compressor. Are there any online tutorials to fix this problem? thanks so much
I'm not aware of any. If you go thru the other comments here, there are some prior discussions and electrical schematic links that you can use to trace the circuit looking for any shorts. When I've found these shorts before myself, they tend to be in places where the wiring, or the wire loom, has been rubbing for many years and the insulation was worn away.
@@DrShock thanks. Unfortunately, I have a 1997 K3500 with a 6.5L diesel engine. The diagrams that are provided are for the 5.7 gas engine. Any idea where to get an appropriate diagram?
I have a 99 6.5L Suburban, the wiring harness there is actually simplier than the gasoline setup. The light green wire coming out of the AC control assy is what you want to trace all the way to the PCM. There's someone who has digitized the 98 service manual, should be fine for your 97 here www.gmt400.com/threads/88-95-service-manuals.43575/ go download the 1998 4_of_4 one, and trace your harness using the schematic on page 6-2304 of that pdf. Pay particular attention to where the harness bundle would rub along the bracket holding the wastegate vacuum solenoid, common wear thru area on 6.5L.
@@DrShock awesome info. My wife and I just traced the entire wiring system . We found no shorts and made sure to check resistance in all connections. Could it be a bad relay? I noticed the relay getting pretty hot in the fuse box. Thanks so much!
Well first, I just noticed your original post said "one is still blowing" and that schematic would be for that MPSA56 power transistor only. Are you saying that one blew out again, or one of the other 2N4403 ones? Just making sure we're talking about the same circuit here.
So to get this straight, my transistor that blew is MPSA56. Should i replace it with the same one or the 2N4403? The one that blew on mine is the hard one on the outside edge under the white screw hole keeper. The difficult one you did.Where did you get the solder sucker?
You should replace it with the same one that ACDelco originally used if its a common number type as I mention in the video. However, be prepared to have a short circuit problem in the AC circuit if it blows immediately again. These transistors either go over a long time (more commonly) due to their just not being quite the right specification for the burden they shoulder or immediately (more rarely) if its a short circuit under the hood.
I have a 1995 K2500 with a/c but no rear defroster. As you know the control heads are non existent or $600+ at the parts house. My temperature control works as it should, when the recirculate button is pushed the fan seems more powerful but the light doesn't come on. The fan speed works as it should, but direction is stuck on floor but when you manipulate the controls to change to head or defog etc. the actuator tries to move a little, blend doors are not binding and you can take the blend door actuator for the air duct and try it on the temperature actuator harness it works just fine proving the actuator is ok?. Also you you press the a/c button a/c does not come on and light does not come on, but the fan direction has a slight movement just like you are changing direction when you press the a/c or recirc button. Could this pesky transistor be the culprit? Thanks
I've personally only repaired this 4X across as many Chevys. In every one of those I didn't run into all of what you're describing, so tough to say for sure. If you're experienced doing electronics soldering, it's a cheap repair from both a parts and time point of view. The blend door actuator definitely wouldn't have anything to do with the control unit button LEDs not illuminating. Worst case you have a bit of both a control unit problem and a blend door actuator (on some models if you power them up unmounted they get out of alignment - rotate past a stop position).
If they reblow, then you have a short in the wiring harness. See some of the older comment discussions where I've given some guidance about following the schematic for the green wire out of the control module and thru the firewall to the underhood area. The transistors that blow like you describe are sinking too much currently, almost always from a small short to ground on this power circuit where a harness has rubbed thru to a metal bracket or other grounded metal surface.
DrShock my truck heater control (kind of like you explained in the video about replacing the heater control and shortly after the heater control is not functioning correctly) when on any zone selection the Defrost stays ON; with the AC on I get continuous air blowing out of the Defrost vent & the same when its switch to the Floor vent, After watching your video I'm thinking that mine could be the same issue with the exact same Transistors have failed, you agree?
The MPSA56 transistor I highlight in the video is effectively a power switch, allowing 12VDC to the AC sensors and actuators circuit. When this transistor goes out, the reason for the floor only air output is the loss of power to the blend door actuator (or zone selection actuator by another name). I've not seen the defroster symptom you describe, but it could be related. You would have to try another control module or attempt the transistor repair on the one you have to know for sure though.
DrShock K, I’ll look for another control unit & try it first. Thanks for your help. At least I know someone out there knows something about these heater/AC control units.
Since I am blowing them rapidly I was wondering if putting a 160 amp alternator might be the culprit or would the electric fan I added have something to do with it?
Ok I have a 1995 HVAC control unit that is having same issues and the transistor numbers are 4692 n434 and 4687 N438 and 2853 N436, all have EBC markings identifying the leads. How do I locate where I can get replacement transistors. I am planning on replacing all transistors on circuit board since this is 25 years old. Any assistance is greatly appreciated.
If you go thru the video description I have some cross mappings there that apply to 1995 as well. You could go with eBay and I have a search link in the description as well. But you could also go with mouser.com too. You don't have to replace all of the transistors, unlike capacitors they are solid state devices. Be sure you have determined you do not have any shorts in the power output part of the harness as that what typically blows out these power transistors. Some of the older comments below will have details on this.
You are like a pro, boss..how do you know if the component is damaged or not if it doesn't leave a mark like burning or a watermark?I n addition to using a multimeter.. can you teach me boss..
You judge this one by the behavior of the control unit. There's no visible signs of the device having failed. You could test the transistor once removed in a tester. Many higher end multi-meters will have a transistor test function built in.
That light green wire is the beginning of a circuit that snakes thru all three pressure switches, the blend door actuator and engine computer. You'll have to check all of that circuit to find a short. Though highly unlikely to be the control module itself (what you are calling a panel) since you have had two different ones with the same outcome now.
It's been a long long time, but I believe it was this one that clued me in on what the problem had to be (though this is a different problem involving a burnt out resistor it got me looking at the transistor) - mechanics.stackexchange.com/questions/42830/1998-chevy-truck-suburban-tahoe-heater-control-not-working-burnt-resistor
The transistor under the hold down bracket is blown on mine. The whole panel was under warranty so they replaced it however after one week of use the mpsa56 transistor blew out again. You mentioned if it does blow right away this would be a short in the green wire. What would it be if it blows several days after being replaced?
Just to be clear, the video I did here is mostly focused on that transistor used as a power switch for the underhood AC circuit and blend door actuator motor. I never mapped out the functionality for the other transistors as I didn't have problems with those. But the one MPSA56 I do go over, that one sinks all the current for the entire AC power circuit. So it typically only blows quickly due to a short to ground in the wiring harness or pressure switch sockets. When it isn't a short it should last months/years before they just die because of the device being a bit marginal for the purpose. It could still be a short, I once worked on a truck where the harness had its insulation worn thru over two decades of engine vibration, only when it would rub against the exposed area would it blow. Took weeks to track it down.
@@DrShock that was going to be my next question. Could it be a bad plug (loose connection) going into the high pressure switch? If its short to ground would it only be that light green wire? Thanks for your help. Awesome video.
Just start from the flat connector out checking for shorts, somewhere lower down in the comments I shared a circuit diagram with someone elses question and that will help you also.
I’m having a similar issue. My air only comes out of the windshield defroster and I also can’t change the temperature of the air either. I changed my head unit and I think while I was doing it something happened.
If this happened suddenly right after work in the same area, then yeah I would suspect something there first. What can happen with the AC control module is the plastic yellows and becomes brittle with age, and the retaining clips to secure the wiring harness can break off letting the connection become loose if it gets disturbed. Worth a look.
Hello, my problem is the air control multi function nob. I turn the vent air on and it blows through the floor vents for a while and then switches over to the air vents. Ac works good just would like to know what could be causing the long delay on switching over like that.
My first reaction is the zone actuator motor that directs the flow to the vents. They can get weak after many years of use. You might want to check around YT for videos around this component, also the blend door motor which does a similar function for hot and cold air mixing.
I tough I had fix the problem .. but no today I drove it n it suddenly turn off just blows air at bottom took it to electrical shop fix it but then happen again
I have the exact same problem and symptoms on my 96 k1500 suburban 6.5 diesel. Control module burns out and does that with the controls almost instantly. Any suggestions?
So what actually causes these transistors to keep going out? I've replaced at least 4 controllers in the last week and all of them had blown transistors.
In the 3 AC assemblies I've repaired this way the transistors are all unbranded. Sadly I think this is a recent thing (not something that happened in the 90s and just poor quality components being used lately, I have replaced the generic transistors with name branded ones of the numbers given in the video and have experienced no further problems whatsoever. I know of others who did this repair before I made the video, and they have more than a year on the same repair with no further problems, again using name branded transistors rather than generics. Now, I haven't hit it, but there is the case where you could get a blowing out of the transistor over and over again (having to redo this repair over and over) and if I had that happening I'd focus on the servo units that activate the blend door involved. These transistors handle the power to those servos. If the door is binding or the servo is dying it could be causing out of spec current draw thru the transistor leading to the failure as well. Though most of the time, it's just shtty lowest bidder type of quality control imo.
I have found on mine a crack in the pcb trail must explain why mine would quit if the plug on the passenger side of the climate control unit was properly plugged all the way in but slide it out a little and my ac would start working
Have a 96 tahoe there ac/ recirculation button do not light up and the temp door or the zone knob do not work i have installed 3 different entire control units one actually is a dorman unit from advanced brand new and still no change.... the green wire on the connector was burned i replaced it And it is getting power but still no difference any suggestions
For the small orange lamps for the recirculation and AC buttons not to work it does sound like a symptom of this same power transistor being out. Have you taken a multi-meter to the output of the green wire coming out of the flat harness (the green wire that goes thru the firewall to the accumulator cycling switch) to confirm 12VDC is coming thru? If not, that transistor has blown on the control unit.
DrShock haven’t yet I’ll check tomorrow when i get off work but id be surprised that all 3 units have blown transitors im thinking it’s a power wire issue (green wire)
Unlikely, if you check the schematic in the service manual (there's some online links in older comments below) the transistor gets power thru the main harness (orange/dark red INPUT), and then switches it out to the underhood harness (green OUTPUT). For those two orange button lamps on the control unit itself not to illuminate I would not expect the problem to involve that green output wire harness (tho it could be something other than the power transistor though). Best bet is to tone it out with the meter and the schematic.
Can someone tell me how to repair this console? My issues are the fan speed only works on Hi.. and the blend door does sound like it is changing, but there is no Heat at all. I did change my radiator cap/thermostat/fan clutch/temp sensors, also burping the system
Fan speed could be either the speed switch, or the resistor pack for the blower motor itself. You would have do a test to see which one is at fault. If the lack of heat is not related to the fan speed, then it could be the heater core needs to be flushed of accumulated debris that is reducing it's efficiency. None of the parts you mention throwing in have anything to do with these symptoms other than somewhat remotely the thermostat.
This needs to be done with some level of pressure, typically with a tool that combines a garden hose water source with compressed air at a low psi. That aside, if I had this problem I'd work on the fan speed first as that can have a subjective bearing on this problem. I'd then verify that the blend door actuator is in fact moving full position to heat, and that the door attached to it is doing the same.
went and had my air system serviced and they managed to have it blowing cold and as hard as it will. he told me that i have missing vents and need to run new ducts. how do i go about doing this?
Ductwork is behind the dash assembly, so they may mean that these have deteriorated and need to be replaced. Vents should be obvious if they are missing as they are in clear sight. These parts were all long ago discontinued by GM, so your options are salvage yard or possibly fabrication on the ductwork itself. Some of the vents, but not all, are available aftermarket. I'm not aware of any aftermarket duct parts though.
Same transistors and procedure applies, but has a difference circuit board layout so the video will not directly match those older ones. I mention in the video description about this.
The transistor I cover in this video is connected to the light green wire that exits the firewall and into the cycling switch on the accumulator, before routing onto other parts of the circuit to the compressor. To blow this transistor, a short on that green power wire to ground is usually required, sinking too much current and overloading the transistor. It can just be a momentary short, such as worn insulation from vibration on the harness. The transistor would blow out within a few seconds.
I have a 1998 chevy z71 all my knows work but the buttons only light up when blower Is off when I turn it on they go off I think it's the resistors I know I spelled that wrong but o well hopefully someone sees this to give me any information
There's a bit more technical info in the video description that might help explain. This video covers a power transistor failure, which has a specific failure signature. But other transistors, and resistors, failing on the logic board could cause other symptoms.
I did this and it fixed everything except now when I push the AC button in it shifts the air flow to the floor and doesn’t even come out cold, I’m at a total loss, I’ve been though 4 control units and tried this on all 4 including an AC delco one and got the same result, except one of the dorman units keeps the airflow on the floor permanently, sos
There's a few other comment threads around where the power output of this transistor goes and some of PDF schematics posted. There's a green wire on the flat cable out of the dash control unit, that travels thru the firewall and under the hood as part of the AC circuit. When this transistor goes you'll no longer have voltage on this particular green signal wire. I'd check this circuit with a voltmeter to confirm you're looking at the right problem. If the transistor is not blown and this wire has a signal, then its not the cause of the symptoms. However, if it's continually blowing the transistor though, then you have a short in this wire under the hood somewhere sinking the current to ground.
@@DrShock Thanks for responding it seems I have some poking around to do but in more detail when I put the ac Delco unit in with the new transistor everything worked but when I hit the AC button I hear the compressor engage and it works for a second or two then the AC button light and recirc button light starts flickering and then the compressor disengages and the air flows to the floor, is it possible that the issue could be related to the VCM? Based off a schematic I’ve seen the circuit goes in and out of the VCM 4 times
That flickering is a sure sign of a short on that power line (green wire) heading out from the transistor to the underhood AC circuit. They can take along while to track down, but the ones I've come across are usually where the harness is next to a metal bracket or fitting where two decades or more of vibration have rubbed thru the wire loom and into the insulation causing a short to ground in that spot. They can be intermittent too, I've replaced a transistor only to have it fail a few days later but in _every_ such instance I traced it to a short in that green power feed circuit under the hood. If you didn't have the flickering indicator lights before it burned the transistor out again I would have suggested something else instead.
@@DrShock Hi again, thanks for your help with this, I finally found some time to get back to this and I’m wondering if you can tell me by word how the AC circuit goes or link me a schematic to follow so I know where to poke around to try to find this short, thank you.
@@nickbriggs7247 There's a few older comments in here and one or two have linked a PDF of the 1998 C/K service manual. That's what you'll need to track down to have the schematic for the A/C circuit. The 98 one is going to be spot on for 96 - 98 pickups and thru 99 SUVs. If you have something older that same website might have an older one as well. idk.
I have the same issue, but would anybody know the proper name of the green selecter switch for the that determines which way the vent is blowing. Please can anybody help!!
So jargon wise, if that's what you're asking, that switch sets the air blend position so you'll hear the device that it controls called a blend door actuator. Sometimes folks refer to it as a zone selector as well. But I guess either are accurate, air blend selection or zone selection.
Hello! I put a brand new ac control unit/panel and I worked for one day and the cold air would only come out of the floor vent even when I had the dial on the face vent. Strange though that in winter time the panel works fine. When I dial in the vents for floor the hot air comes out through the floor, same for defrost, etc. But as soon as I would push in the ac button to test it out, the cold air would come out of the vent for floor only. Last year I happen to turn on ac even though cold air was coming out from floor vent. Well as soon as I turned it on the whole electrical system went out! I had to pull my truck with my Pop's truck back to the shop. I pulled off the shroud. I moved the harness connection on the left and all the electrical came back on. I have not messed with it since then. We are now in summer and it gets very hot here. Do you have any suggestions on what I should troubleshoot. Also, I would have liked that you had shown the public on how to test those bad transistors. I do not know much on electrics. Anyways, thank you for your video!
I think you would find, for this particular videos scope, that you have a short circuit somewhere in your wiring harness. Can't speak to the whole vehicle outage, as any short like that should have blown one or more fuses. But short to ground you do have, at least one. The power transformer in the control module is blowing because of a short in the circuit on the green wire coming out of the harness into the pressure switch located on the AC accumulator. From there you will have to follow the harness circuit to other switches and eventually the powertrain control module (or engine control module depending on the vehicle). The circuit varies between diesel and gasoline vehicles so a service manual is a must. I don't show testing those transistors because it's not a best practice to put them back, mylar circuit boards are not intended to be repaired like this. GM intended you to throw it away and buy a new one. So to minimize damage just install new transistors always, they are cheap. If you have the symptoms described in the video description, and only those symptoms, it's unlikely to be anything else but the transformer getting burned out. I would say you have more than this, as you experienced a larger electrical outage which would not be possible just from the problem in this video.
Okay one day my AC and air condition motor no medium high switch work blower stop so I'm like okay what happened so I turn the knob back on and off and the blower change back on next couple of days it stopped working again I replace the relay switch still not working somebody talk to me please
If the problem is just some of the blower motor settings for AC stopped working, I'd suspect the selector switch. Not sure what you mean by _relay switch_ but I'm referring to what I go over in this other video - ruclips.net/video/Gl5_CEJdu4o/видео.html
Definitely wanna go salvage yard on that, cheapest route best fit. If there's an LKQ yard in your state that's where I'd go, that's a you pull it yard.
There are alot of makes, but newer more likely to be ON Semi or Vishay. Its a very common component from many suppliers. Small quantity eBay may end up being cheaper but Mouser.com is another option.
You just saved me over $200. Thank You
Just buy a new one please
@@cornell833 why?
I have owned a 97 GMC K1500 with 5.7 for 25 years. I have rebuilt or replaced almost every component on this truck and we are still driving it today. The A/C has been problematic for a few years. I watched your video and noted that the control was the only component that was still original. I discovered yesterday a long time refrigerant leak was due to the low side Schrader valve leaking. After replacing it, the A/C once again blows 43 degree air but mainly out the lower vent and defroster. I see that the actuators are working but I suspect the air box door is not properly diverting the air to the center vents. Believe me, the removal of this dash is not easy! Having done it twice before, yesterday I found a quick, cheap solution: a $15 plug in fan I clipped to the dash by the lower vent. Man, does it blow that cold air from the vent up in my face! I know this is not the proper way to fix it, but it is an old truck and I have A/C again to face our Texas summer. This was an intriguing video, but unfortunately it was not a fix for mine. Keep up the good work. We RUclipsrs need good content like this!
I think the 4692 is an NPN transistor, at least it checks as one. I did a 95 truck today and it has 4 transistors. 4687,2857 were replaced with 2n4403. This fixed the issue. There are (2) 4692 near the potentiometers. I did not replace them, no need to tempt fate. The 2n4401 would be used there. I did another 95 a few years(7) back and used the mpsa56 and mpsa06 in the 4 spots. It works fine still. Fine Video, I sure wish I had it when I did the first one.
I have a 1996 C3500 6.5 Diesel with the same problem as yours. I will try this repair. Thank you so much for sharing this video. I would have never known how to fix this. Thank you
I did something I almost NEVER do, I replaced mine through Rock Auto with a "Standared Motor Parts" (when I was young, Standard supplied the highest quality points and condensers you could buy). They may be a China company now. But, they offered a 3 year warrenty as compared to OEM ACDelco of 90 days. It works perfect and was (I think around $150.00) and is well past 90 days. However, after seeing yet another astonishing RUclips of yours, I am going to get my original and see if I can fix it from what you have taught us all here. Amazing!
Agreed! I bought a replacement but now that I have no risk, I will fix. Why? Because we are men and we are curious! Lol
1999 GMC Yukon. All settings seemed to work fine until I installed car stereo. Somewhere during that time I smelled something burning. Stereo works great. Now no lights come on on the climate panel and air comes through vents for 1 second then automatically shifts up to dash defrost vents. Right knob does nothing now. Middle knob makes blend door actuator move as before, but no heat, though air comes out vents as powerful as before, and fan speed switch works fine on all levels. I'm going to do what you did, but only after buying a part. Then I'll have a spare part around in case this happens again. I assume there must be a short in the harness to the climate panel. Only a few inches of wire have become damaged somehow. I will re-assemble the dash before I re-attach negative battery cable to prevent wiggling the wires and possibly re-damaging the new panel. Thank you very kindly. BTW mine doesn't have the rear defrost button, I only have defrost on the mode switch. Does this mean the plugs in the back won't match up with a 3 button panel?
With age the chances for a harness short when fiddling in that radio area are far higher, as the wiring insulation brittles up.
Rear defrost was a factory option, so not having it doesn't change the rest of the repair/connections advice. Just that you would have unconnected or uninstalled wiring because your truck wasn't built with that option originally is all. I believe I give the GM part numbers for all the panels in the video description, so that you can track down the same one, if you like.
@@DrShock Liked and subscribed. Very useful info. I just ordered the part. Thank you immensely!
That's what I was doing messing with the radio is that what fried the box on mine
thank you for your video! I had a friend change out the resistors. So far so good. Thanks again!
Just remember these transistors sometimes go because of a short in the underhood wiring too. So if it goes again, that's what you have to hunt for.
Thanks for the video friend showed up on hottest day of the years Im in Phoenix 113 today her AC stopped working on her 96 suburban. I traced the problem to the control module after replacing the 50 amp AC fuse. I ordered a replacement AC delco module noticed it wasn't the the correct one she had rear defrost. After removing the old control module I noticed the problem the resister you said blows out was blown. I plugged in the replacement AC control mod I got on Amazon to see if the compressor would turn on well as soon as I pushed the AC button the transistor smoked in the new one. I crossed ref the numbers and they cross over to NTE159. Im headed to Frys electronics see if it will fix it but I suspect it will burn up again. The only thing I noticed was the AC relay might have been installed backwards didn't match the relay next to it that is under the hood in the fuse box with the 4 other relays and maxi fuses. The Transistor is 800ma PNP if it blows again i'm only out the $3
@blastman8888 when the transistor blows that fast it's a sure sign you have a short to ground in the circuit. That transistor supplies the +12VDC battery power to the circuit when activated and it exits the control module thru the light green wire on the passenger side flat connector into it. You can trace this light green wire coming out of the firewall into the engine bay, usually it starts with the pressure switch on the accumulator and then works its way over to the other other pressure switches and then the main computer. After a couple of decades like these trucks have you're going to have vibration/rub burns thru the wiring insulation somewhere causing the short. I'm going to presume you have a gasoline engine (diesel AC circuit is quite different) here's a couple of 1998 circuit diagrams that should help www.2carpros.com/images/question_images/204058/original.jpg and www.2carpros.com/images/question_images/204059/original.jpg . Just follow that light green wire out of the 'AC Switch' shown on the left of the first diagram and then thru the rest of the circuit until you find the short.
@@DrShock Thanks for the reply I will take a look at the wiring when I get a chance I removed the control module and AC relay I don't see any shorts with my meter to ground with and without both pressure switches jumper's inserted in the plugs at the relay plug. I was wondering if the Blend door air vent motor could be shorted and overloading that same green wire feeds that motor. After reading this www.silveradosierra.com/how-to-articles/how-to-repair-gmc-ck-series-trucks-hvac-control-unit-t77522.html he says the only propose of this transistor is shut off power to the control module when it see's 12V from the blower indicating the blower is shut off. This was designed to turn off the compressor when the blower was not running to keep it from icing over. He suggested jumper the transistor emitter to collector leads and add a relay to cut out the compressor. When you turn the blower on any speed the 12 V goes to 0v on the bias leg of that transistor though those resistors to make it switch 12 V on power the module up. It's a strange design not sure why GM would even bother with all that seems lot easier to just have knob shut off power to the control module when turn it to off.
This short I was talking about is going to be under the hood, not in the cab wiring. You have to trace and meter out the entire circuit across all three pressure sensors one at a time and to the PCM as well as to the left hand air flow blend door (not the temp blend one near the heater). What that guy is telling you in the article is not incorrect, but you're misunderstanding (I think) from his writeup that this transistor is making the connection for 12VDC to the ENTIRE AC CIRCUIT under the hood! That's what the little transistor does. If you have a short, following that article is not going to remove that situation and just leave you with then a burnt out fuse or worse - a burnt out PCM. I'd still strongly suggest the transistor blowing is a symptom of a short circuit here, just friendly advice. One you fix that sure, you could alternatively follow this guys advice to remove the weakness in the transistor design during normal workloads. But that short has to get fixed first.
@@Mike-01234 I am having the exact same problem as you (1996 Suburban K2500, 7.4L, Gas). I am on my third control module. Two used ebay ones and one brand new from Rock Auto. Each worked perfect and everything works but my "Max" A/C as that servo on the far right needs to be replaced and just "ticks" if activated so I never allow it to be powered. It is unrelated to the problem. It seems a random short just smokes the transistor. I tried using a DVOM to see if the light green wire at the flat connector would ground out. I could not shake it or move it and get it to ground out. I am thinking of just replacing it (light green wire) with a new wire full length and trying that. How are you doing and what have you done if you fixed yours? Thanks very much!
great video my problems exactly! Replaced climate control module 1 month ago! I went to the junk yard today pulled a control panel out of another suburban and put it in mine now everything works great again! pulled the brand new control panel out and it says made in china complete junk! bought the new one from Napa, so if you have this problem just find a working one from the junk yard! my new one from Napa only lasted one month before transistor failed! QUESTION can you switch control board from the old one that works to the failed one I got from Napa?
I have the same problem. Air blows out dash vents for 1 second when first turning key on, then I hear the actuators move, and no air from anywhere, but still can hear it blowing somewhere. Going to buy a new Dorman control module and hope it fixes the problem.
👍👍👍👍 so happy did. what you said works perfect! A hole 1.49 each 😀
Preformed this fix on a cheap Chinese controller and it the AC started working again. Got the parts for like $5 at an electronics store.
Working on replacing the relays in my transfer case control module and it should solve my 4x4 issues. I replaced the capacitor on the board and only one relay would fire. It puts it into 4x4 but won't take it out.
Really helpful thanks. Bough a new one like $170 and installing it got burn again a gave up until I see this
Does getting a new one fix it or will it just screw up after a while
@@barryhaire7424 It's usually burning the transistor out due to a short somewhere in the harness. I've seen these where it's just a rub thru somewhere along the harness and it's intermittent when it will touch the engine and create that short to ground that kills these little transistors. Sometimes it can be from a momentary power spike though, in which case a replacement will be enough. Hard to say over an internet comment forum, every situation is unique.
@@DrShock ok thanks I have a 1996 sonoma that the ac is doing just like In the vid but I don't have the tools or skills to do what u did so I was wondering if it would be a waste of money to buy a new module
@@barryhaire7424 In your situation, then I might be more inclined to try a salvage yard pull first to inexpensively see what happens before spending on a new one. You'll of course want to pick a truck that was in an accident vs one sold off from being inoperative, to increase the probability its AC was still working.
@@DrShock ok will do thanks
Amazing fix and a lot better than spending $200.
I can't thank you enough! so happy right now!
Where do you recommend getting those little transistors?? Subscribed!
Btw, one of my rear defoggers on my Dutch doors stopped working. What all could I do to diagnose the cause?
There's a link in the description for them. On the defogger, each door has it's own grid when you don't have the liftgate option. When you have the liftgate, which I presume is what you mean by dutch being it's a top half lift up glass door, there's only one grid. What usually goes wrong is you get a break in the brown wire grid that sticks onto the inside glass. But it can also be the door contact switches. If I had this problem I'd do a visual inspection of the grid, and check the fuse and relay for the defogger circuit. If those looked good I'd check the door contact switch assembly. Tools wise a voltmeter and test light along with a copy of the schematic to get started. You can find that schematic in the PDF of the service manual here - www.gmt400.com/threads/88-95-service-manuals.43575/
Great video! Bummer that your new selector console had a bad transistor though. Where did you find the new selector console? ANd how much? I just bought a console on eBay and it is in worse shape than mine, and plugged it in to find the same issue still occurring with the blower stuck on floor only, which led me to you. Still watching this now, haven't tried yet. Interestingly I had just replaced my blower motor prior to this selector switch going out.
So the replacement control module did not have a bad transistor, there was a short in the underhood engine AC wiring that was burning them out which is a common cause for this after a couple of decades of vibration the harness insulation wears thru in some spots. That particular short can be difficult to trace down, as often it only shorts on certain driving conditions (like over railroad tracks). I recommend only buying brand new, never used, on this part due to the way the plastic degrades with age the mounting tabs *will* yellow and break off. eBay can be an inexpensive source of new old stock parts, or rockauto.com for brand spanking new.
@@DrShock so are saying that you replaced the transistor on the new module in video right? And then said it worked at end of video? But then after driving a bit, burnt out again? @DrShock @DrShock when I was looking at my wiring, following from condenser and firewall etc. It is all wrapped up well and covered with the plastic tubing. So I cant really imagine that has happened here, but it's possible. I dont think it's the actuators, because none of them move at all when turning zone selector. The door flap for floor moves freely by hand. All the fuses look good, wires look good, ground locations look good. Connectors look clean. Think I just bought a used console with same issue baked into it? I do remember around the same time this went out that my radio must have shorted out or something because the music went from all the speakers playing to just the rear for a few seconds, and then the music came back to all speakers. I think that since my clips are broken on my selector console, and it has this open/expossd circuit board, that it bounced and touched the metal radio casing. That's about all I can see that would do it. I wonder if i should attempt to replace my transistor or not? Quite a coincidence that the used one i just bought has same exact issue.... i don't like that, makes me think something else is going on but I guess trial and error is the way to find it.
In my case I had the AC control module go out that was an ACDelco installed new and around 10 years old. The brand new ACDelco replacement died after a week which made me think at the time it was poor quality transistors. That prompted me to research the problem, trace down to this transistor and replace it and do this video. Later on I worked on this same problem on a different truck, and knowing this now I was able to trace the problem to a worn spot on the harness to the compressor creating a short in the circuit that this transistor feeds power into. So now I tend to suspect shorts as the cause for these transistors burning out every time. There's a few very specific symptoms of this particular problem I summarize in the description. If you don't have those, or have other things going on like the radio behavior, it could be you have multiple electrical problems going on.
@@DrShock well that story about your new replacement selector module and replacing the transistor doesnt really make sense to me, because where is your truck wiring shorting out then? You didn't find a short on your wires, but you did replace a bad transistor right? And dont you find it funny that a short is always blowing this same transistor, and resulting in the same single zone indicator knob dysfunction?And the short occurring with same exact wire?? Rather than wrecking the other components of the module? Funny it's always the zone selector gone bad, but all the rest works fine. It would be pretty rare for that one single wire, wrapped up and clustered with all of the rest of the wires, about 8 of them, to be the one single wire shorting everytime, and just that one single wire, none of the others. That radio thing I described happened one time, and is working fine ever since, it lasted about 5 seconds that's what I think may have touched the module with the metal radio case because the clips on module were broken allowing it to bounce up and touch radio. But I dont know for sure, just hypothesis. Otherwise I cant figure out why my zone selector went out on me, dont see any wiring issues, no shorts, or exposed wires. And my symptoms are the exact same thing that you have described, just the zone selector stuck blowing on floor in my original module, as well as the used one I just bought on Ebay, which also has broken mounting clips incidentally, but I didn't touch metal radio with circuit board myself on that one. So I guess my question is after you replaced your transistor on the replacement module, have you had the issue come up again on your truck? If not, does not really indicate a short circuit on your truck does it? And are you saying that you replaced a perfectly good transistor on your replacement module? I dont understand here, why didn't you repair the original one? I get that the other truck you worked on may have had a wiring short, but it seems this is a very common issue with these climate selector modules judging by the views and comments on the video. So idk, I think you were probably correct initially that these transistors will go out on that one zone selector only. Please let me know what you think, I appreciate the input and the attention to this matter. I am sort of racking my brain here and spent all day monkeying with these damn modules, looking over wires, looking over door actuators, fuses. The fact this other used module I bought has the exact same symptoms right off the bat upon plugging in, kind of detracts from your wiring short theory as well I believe.
Alot of questions here. I'll try and touch on them. You would use a transistor tester, a function on most high end digital multi-meters, to test the semiconductor before making a determination it's defective. So yes, it's straightforward to confirm the diagnosis with the right tools. Consulting the electrical schematic of the service manual, you'll find several flavors depending on the engine and fuel type. In all cases this particular power transistor feeds the power to the cycling switch first as it enters the engine bay from the dash. It's a green colored wire in the harness. The power feed then takes different wiring harness paths, and sometimes thru pressure switches too, for each engine type differently on its way to the AC compressor. The other transistors in the control module serve other purposes, some control the blend door signals, for example. So they wouldn't have anything to do with the power feed. In my experience transistors are fairly robust, what kills them is sinking alot of current quickly (a short), or overwhelming them with a rapid power surge (static electricity discharge for example). I've done this repair on several trucks now, and where I had the case of the transistor blowing out _every time_ it's *always* a short in the harness. Where you don't then it's more likely just that transistors day to die and nothing more to it. The only way to find out is remove the transistor, test it, and if bad replace it and see what unfolds from there.
Great video! thanks!!
Great job for diy thanks
I have a brand new unit in my truck already. The problem I have is that it blows air wherever it feels like. It doesn't matter where I set it. Floor, defrost, or vents I sometimes get vents sometimes defrost, sometimes floor, but most the time all of them. It's okay in the summer when it's just the A/C, but in the winter in ND it's not so good when you need as much heat on the windshield as possible. Have you ever run into this or heard of this?
If the vent and AC controls work (AC compressor turns on as expected, just outside air flow when expected) and the temperature blend works (ratio of cool to heat is as set) and the fan speeds are all working as expected, that would leave just the actuator motor for the zones. On these trucks it's to the right of the accelerator pedal and controls the flap/door that directs the air. If all the above are true, that would only leave that motor, or the flap itself, to check out.
@@DrShock Great, that's what I will look at then. Thanks for the reply and keep up the great work
SAME PROBLEM ON MY GMC TRUCK 95 , WILL REPLACE TRANSISTORS AND SEE IF IT WILL FIX MY PROBLEM
THANKS FOR THE VIDEO SIR
Having issues with new AC Delco A/C Controler. Would appreciate a one on one take about my problem with my 96 6.5 diesel.
If its related to this video go ahead and elaborate by comment and I'll see if I can give some advice.
OK. Now my New "Standard" one failed exactly as my ACDelco. Small puff of smoke out the right side of the control until then the exact symptoms you describe. I examined both ACDelco and Standard and failure was the same. So it appears I have an intermittent short. Could you please dumb it down and explain how I find this short that has now blown that transistor on both the original ACDelco and the new replacement? Again, both assemblies failed the same with the same symptoms you described in failure. 1996 GMC K2500. Thank You!
When they go intermittently like that, in my experience its a place where the harness has rubbed thru the insulation and is making contact to the engine ground somewhere intermittently. Very unlikely to be behind the dash, more likely under the hood so start there. If you go thru some of the older comments on this video, there's a thread with a PDF link to the GM service manual posted 6 months back where you can find the wiring schematic. This can help you follow the harness colors under the hood searching for any physical damage in the spots where it comes in contact anywhere metal. The damage can be very small! So a magnifying glass might be helpful. You're looking for bare copper showing no matter how small. The fix can be simply electrical tape short term, but longer term to wrap in some tough plastic piece to deal with the rubbing.
Also I should mention to check the refrigerant pressure switches for damage / shorting at their connectors (but do not remove them) as you follow the green colored wire in the schematic around to the compressor.
@@DrShock Thanks again. I must be missing something. I read all the posts and looked at the two views of the wonderful color schematic. All I can see is the light green wire going directly from the A/C Control module to the A/C high pressure cut out switch. From there to the CPU. I see no other routes as others have referred to. It seems like the easy thing is to just splice in a new (equal or better gauge) light green wire from the harness connector at the A/C Control Module to the HP Switch and then a new wire from switch to CPU. What am I missing?? Another thought: What about the ground wire going through the same harness at the A/C Control Module to gound up under the dash?? Couldn't a bad ground cause an over-current situation (I'm a mechanical guy not an electrical guy)?? It would be easy to splice an auxiliary ground from the existing black wire to some easy place under the instrument panel or behind the A/C Control module. I would greatly appreciate your more experienced and knowledgeable thoughts on this. I'm getting frustrated and am spending too much money on A/C Modules. I did order the transistors you recommended and will be trying to repair two modules that I have blown.
The wiring can vary with every engine even in the same model year for the AC. The 6.5L diesel V8 has the most connections with this particular light green wire circuit. Looking at the 5.7L Vortec V8 (page 6-1675 in the service manual) yes its just the high pressure cutout for that engine as well as the 5.0L V8. The 7.4L V8 schematic is on page 6-2789. That light green wire is directly connected from the transitor on the control module logic board to the high pressure cutout switch and then to the VCM/PCM pin C3 on all the gasoline V8s. If you see no insulation damage under the hood, I would check from the firewall back inside to the control module harness connector itself then. It would not be the ground shorting out the transistor, what's burning it up is sinking too much current. Ground problems would leave you intermittent or no function at all. I would also try disconnecting both the control module harness and the PCM/VCM connector C (both ends). And then seeing if you are getting continuity to ground on the light green wire from either end, highlighting a short to ground (do this test with a helper to wiggle around the wire harness during the test as well at both ends). If so, I'd then disconnect the high pressure switch connection and try again (to see if it is the switch that is shorting in some way internally). If its not the switch then you would still have a short somewhere, perhaps more likely on this engine from the switch to the VCM/PCM than the other part of the circuit. These can be very difficult and aggravating problems. Definitely one of those walk away for a bit and retry ones.
@@DrShock Great advice. I have 7.4 Gas so it is direct. I think the easiest thing is to just run my own wire from the A/C Module to the HP Switch and then from the Switch to the PCM. (From my experience it would be highly unusual for the switch to short to ground, but who knows!) It will take less time than a propper diagnostic as I have to work alone. My transistors arrived today so will take one A/C Module with replaced transistor, and then replace light green wire & green with white wire (I think) from switch to PCM and just see if it blows the transistor again. I will update this posting after I try that. Thank you again for all the valuable lessons and advice.
I ordered all new plugs for the three pressure switches. They all seemed loose and stretched out. We had problems with others before on the engine. I still feel though we have a wire directly touching some metal somewhere.
I am facing this problem one or tow times a year. Chevy 1997
Thank you
You likely have a wiring harness short then, read thru some of the older comments for tips to diagnose and locate.
I have the 1996 GMC Yukon 2 door 4x4. It does NOT have AC or a redefroster. The Climate Control Module temperature knob is broken off. No I do not have the knob any longer. The PART is no longer supported by GM. I am looking to replace the entire module as the knob seats on a stem which is what is broken. Any leads are helpful
Your best bet on a part like this is a you pull it salvage yard. Like an LKQ PYP (Pull Your Part) or similar. AC delete would have been a fairly rare build for the late 1990s. Another option is to have your local GM dealer dig up the part number for the heater only control assembly, and put out some eBay and the like searches for an NOS one. Likely will take a very long time to get a hit though.
Were did you get the parts?
There's a link in the video description for eBay on these parts
Can a "dragging" blower blow the resistor I've literally pulled the entire dash trying to find a short and cant find one
When you say resistor did you mean to say transistor given this video? Or are you talking about an actual resistor elsewhere on this same control unit circuit board? For the transistor the answer would be no, has nothing to do with the blower motor circuit. In my experience the only shorts that blow this transistor are either on the control unit, over voltage on the incoming power harness, or a short to ground on the outgoing power harness (the green wire on the flat connector heading into the accumulator cycling switch first and then onwards).
@@DrShock yes I ment transistor I put a new control panel in and within 30 seconds it fired the transistor and went back to not working i guess I'll retrace the green wire once more
I replaced the transistors, but one is still blowing our after replacement. I understand that there may be a short from the control unit harness to the high pressure cutoff switch on the back of the AC compressor. Are there any online tutorials to fix this problem? thanks so much
I'm not aware of any. If you go thru the other comments here, there are some prior discussions and electrical schematic links that you can use to trace the circuit looking for any shorts. When I've found these shorts before myself, they tend to be in places where the wiring, or the wire loom, has been rubbing for many years and the insulation was worn away.
@@DrShock thanks. Unfortunately, I have a 1997 K3500 with a 6.5L diesel engine. The diagrams that are provided are for the 5.7 gas engine. Any idea where to get an appropriate diagram?
I have a 99 6.5L Suburban, the wiring harness there is actually simplier than the gasoline setup. The light green wire coming out of the AC control assy is what you want to trace all the way to the PCM. There's someone who has digitized the 98 service manual, should be fine for your 97 here www.gmt400.com/threads/88-95-service-manuals.43575/ go download the 1998 4_of_4 one, and trace your harness using the schematic on page 6-2304 of that pdf. Pay particular attention to where the harness bundle would rub along the bracket holding the wastegate vacuum solenoid, common wear thru area on 6.5L.
@@DrShock awesome info. My wife and I just traced the entire wiring system . We found no shorts and made sure to check resistance in all connections. Could it be a bad relay? I noticed the relay getting pretty hot in the fuse box. Thanks so much!
Well first, I just noticed your original post said "one is still blowing" and that schematic would be for that MPSA56 power transistor only. Are you saying that one blew out again, or one of the other 2N4403 ones? Just making sure we're talking about the same circuit here.
So to get this straight, my transistor that blew is MPSA56. Should i replace it with the same one or the 2N4403? The one that blew on mine is the hard one on the outside edge under the white screw hole keeper. The difficult one you did.Where did you get the solder sucker?
You should replace it with the same one that ACDelco originally used if its a common number type as I mention in the video. However, be prepared to have a short circuit problem in the AC circuit if it blows immediately again. These transistors either go over a long time (more commonly) due to their just not being quite the right specification for the burden they shoulder or immediately (more rarely) if its a short circuit under the hood.
Thank you. you will have information about the diode associated with that transistor?
No, I haven't had cause to look into that component.
Do you suggest general purpose transistors? Also, do you suggest a specific brand?
No specific brand, the numbers are more important. General purpose rating is fine yes.
@@DrShock Thank you sir!
I have a 1995 K2500 with a/c but no rear defroster. As you know the control heads are non existent or $600+ at the parts house. My temperature control works as it should, when the recirculate button is pushed the fan seems more powerful but the light doesn't come on. The fan speed works as it should, but direction is stuck on floor but when you manipulate the controls to change to head or defog etc. the actuator tries to move a little, blend doors are not binding and you can take the blend door actuator for the air duct and try it on the temperature actuator harness it works just fine proving the actuator is ok?. Also you you press the a/c button a/c does not come on and light does not come on, but the fan direction has a slight movement just like you are changing direction when you press the a/c or recirc button. Could this pesky transistor be the culprit? Thanks
I've personally only repaired this 4X across as many Chevys. In every one of those I didn't run into all of what you're describing, so tough to say for sure. If you're experienced doing electronics soldering, it's a cheap repair from both a parts and time point of view. The blend door actuator definitely wouldn't have anything to do with the control unit button LEDs not illuminating. Worst case you have a bit of both a control unit problem and a blend door actuator (on some models if you power them up unmounted they get out of alignment - rotate past a stop position).
I did this to two contol modules and it fixed mine for about a week and back to the same problem. Put the other in and it did not work at all.
If they reblow, then you have a short in the wiring harness. See some of the older comment discussions where I've given some guidance about following the schematic for the green wire out of the control module and thru the firewall to the underhood area. The transistors that blow like you describe are sinking too much currently, almost always from a small short to ground on this power circuit where a harness has rubbed thru to a metal bracket or other grounded metal surface.
DrShock
my truck heater control (kind of like you explained in the video about replacing the heater control and shortly after the heater control is not functioning correctly) when on any zone selection the Defrost stays ON; with the AC on I get continuous air blowing out of the Defrost vent & the same when its switch to the Floor vent,
After watching your video I'm thinking that mine could be the same issue with the exact same Transistors have failed, you agree?
The MPSA56 transistor I highlight in the video is effectively a power switch, allowing 12VDC to the AC sensors and actuators circuit. When this transistor goes out, the reason for the floor only air output is the loss of power to the blend door actuator (or zone selection actuator by another name). I've not seen the defroster symptom you describe, but it could be related. You would have to try another control module or attempt the transistor repair on the one you have to know for sure though.
DrShock
K, I’ll look for another control unit & try it first.
Thanks for your help. At least I know someone out there knows something about these heater/AC control units.
The one i have the AC button not responsive, looks like replacing these transistors will also fix.
Where can I buy these transistors at???
There's an eBay search link in the description
Since I am blowing them rapidly I was wondering if putting a 160 amp alternator might be the culprit or would the electric fan I added have something to do with it?
Nope, this is an isolated circuit only for the AC
Ok I have a 1995 HVAC control unit that is having same issues and the transistor numbers are 4692 n434 and 4687 N438 and 2853 N436, all have EBC markings identifying the leads. How do I locate where I can get replacement transistors. I am planning on replacing all transistors on circuit board since this is 25 years old. Any assistance is greatly appreciated.
If you go thru the video description I have some cross mappings there that apply to 1995 as well. You could go with eBay and I have a search link in the description as well. But you could also go with mouser.com too. You don't have to replace all of the transistors, unlike capacitors they are solid state devices. Be sure you have determined you do not have any shorts in the power output part of the harness as that what typically blows out these power transistors. Some of the older comments below will have details on this.
You are like a pro, boss..how do you know if the component is damaged or not if it doesn't leave a mark like burning or a watermark?I n addition to using a multimeter.. can you teach me boss..
You judge this one by the behavior of the control unit. There's no visible signs of the device having failed.
You could test the transistor once removed in a tester. Many higher end multi-meters will have a transistor test function built in.
Could the high pressure switch be bad? I don't see any issues with the light green wire, seems fine. Could it be a bad ground on the panel wiring?
That light green wire is the beginning of a circuit that snakes thru all three pressure switches, the blend door actuator and engine computer. You'll have to check all of that circuit to find a short. Though highly unlikely to be the control module itself (what you are calling a panel) since you have had two different ones with the same outcome now.
@@DrShock I will start with the plug connectors and inspect all plugs. Then a visual check if the wires.
Thank you so much for the help.
D
Could you provide part numbers and where you purchased them? And where you placed each one in order?
There's an eBay link in the video description. I prefer eBay on these types of parts. The description also has some more details that may help.
by the way, what forum did you read on the chevy ac controls...
It's been a long long time, but I believe it was this one that clued me in on what the problem had to be (though this is a different problem involving a burnt out resistor it got me looking at the transistor) - mechanics.stackexchange.com/questions/42830/1998-chevy-truck-suburban-tahoe-heater-control-not-working-burnt-resistor
The transistor under the hold down bracket is blown on mine. The whole panel was under warranty so they replaced it however after one week of use the mpsa56 transistor blew out again. You mentioned if it does blow right away this would be a short in the green wire. What would it be if it blows several days after being replaced?
Just to be clear, the video I did here is mostly focused on that transistor used as a power switch for the underhood AC circuit and blend door actuator motor. I never mapped out the functionality for the other transistors as I didn't have problems with those. But the one MPSA56 I do go over, that one sinks all the current for the entire AC power circuit. So it typically only blows quickly due to a short to ground in the wiring harness or pressure switch sockets. When it isn't a short it should last months/years before they just die because of the device being a bit marginal for the purpose. It could still be a short, I once worked on a truck where the harness had its insulation worn thru over two decades of engine vibration, only when it would rub against the exposed area would it blow. Took weeks to track it down.
@@DrShock that was going to be my next question. Could it be a bad plug (loose connection) going into the high pressure switch? If its short to ground would it only be that light green wire?
Thanks for your help.
Awesome video.
Just start from the flat connector out checking for shorts, somewhere lower down in the comments I shared a circuit diagram with someone elses question and that will help you also.
I’m having a similar issue. My air only comes out of the windshield defroster and I also can’t change the temperature of the air either. I changed my head unit and I think while I was doing it something happened.
If this happened suddenly right after work in the same area, then yeah I would suspect something there first. What can happen with the AC control module is the plastic yellows and becomes brittle with age, and the retaining clips to secure the wiring harness can break off letting the connection become loose if it gets disturbed. Worth a look.
Hello, my problem is the air control multi function nob. I turn the vent air on and it blows through the floor vents for a while and then switches over to the air vents. Ac works good just would like to know what could be causing the long delay on switching over like that.
My first reaction is the zone actuator motor that directs the flow to the vents. They can get weak after many years of use. You might want to check around YT for videos around this component, also the blend door motor which does a similar function for hot and cold air mixing.
I tough I had fix the problem .. but no today I drove it n it suddenly turn off just blows air at bottom took it to electrical shop fix it but then happen again
I have the exact same problem and symptoms on my 96 k1500 suburban 6.5 diesel. Control module burns out and does that with the controls almost instantly. Any suggestions?
Usually a short to ground somewhere in the wiring harness. The comment history here may have some schematic pointers.
So what actually causes these transistors to keep going out? I've replaced at least 4 controllers in the last week and all of them had blown transistors.
In the 3 AC assemblies I've repaired this way the transistors are all unbranded. Sadly I think this is a recent thing (not something that happened in the 90s and just poor quality components being used lately, I have replaced the generic transistors with name branded ones of the numbers given in the video and have experienced no further problems whatsoever. I know of others who did this repair before I made the video, and they have more than a year on the same repair with no further problems, again using name branded transistors rather than generics. Now, I haven't hit it, but there is the case where you could get a blowing out of the transistor over and over again (having to redo this repair over and over) and if I had that happening I'd focus on the servo units that activate the blend door involved. These transistors handle the power to those servos. If the door is binding or the servo is dying it could be causing out of spec current draw thru the transistor leading to the failure as well. Though most of the time, it's just shtty lowest bidder type of quality control imo.
Your alternator or voltage regulator might be bad , if your alternator is producing more than 15 volts then that's what it is
I have found on mine a crack in the pcb trail must explain why mine would quit if the plug on the passenger side of the climate control unit was properly plugged all the way in but slide it out a little and my ac would start working
Easy salvage yard fix to replace the board from a donor, see if you have an LKQ facility near you. They let you pull the parts yourself.
Have a 96 tahoe there ac/ recirculation button do not light up and the temp door or the zone knob do not work i have installed 3 different entire control units one actually is a dorman unit from advanced brand new and still no change.... the green wire on the connector was burned i replaced it And it is getting power but still no difference any suggestions
For the small orange lamps for the recirculation and AC buttons not to work it does sound like a symptom of this same power transistor being out. Have you taken a multi-meter to the output of the green wire coming out of the flat harness (the green wire that goes thru the firewall to the accumulator cycling switch) to confirm 12VDC is coming thru? If not, that transistor has blown on the control unit.
DrShock haven’t yet I’ll check tomorrow when i get off work but id be surprised that all 3 units have blown transitors im thinking it’s a power wire issue (green wire)
Unlikely, if you check the schematic in the service manual (there's some online links in older comments below) the transistor gets power thru the main harness (orange/dark red INPUT), and then switches it out to the underhood harness (green OUTPUT). For those two orange button lamps on the control unit itself not to illuminate I would not expect the problem to involve that green output wire harness (tho it could be something other than the power transistor though). Best bet is to tone it out with the meter and the schematic.
Also, the fan speed is not blowing high enough, could same transistor be at fault?
Nope, totally unrelated.
@@DrShock Could just be the blower motor
Crap, I didnt check the fuses, looks like it could be a problem, but would be very concerned why the fuse blew.
Can someone tell me how to repair this console? My issues are the fan speed only works on Hi.. and the blend door does sound like it is changing, but there is no Heat at all. I did change my radiator cap/thermostat/fan clutch/temp sensors, also burping the system
I don't mind the fan speed, but I just want heat in the truck
Fan speed could be either the speed switch, or the resistor pack for the blower motor itself. You would have do a test to see which one is at fault. If the lack of heat is not related to the fan speed, then it could be the heater core needs to be flushed of accumulated debris that is reducing it's efficiency. None of the parts you mention throwing in have anything to do with these symptoms other than somewhat remotely the thermostat.
@@DrShock oh I forgot I flushed the heater core. Ran water thru the inlet and outlet. like 3x.
This needs to be done with some level of pressure, typically with a tool that combines a garden hose water source with compressed air at a low psi. That aside, if I had this problem I'd work on the fan speed first as that can have a subjective bearing on this problem.
I'd then verify that the blend door actuator is in fact moving full position to heat, and that the door attached to it is doing the same.
went and had my air system serviced and they managed to have it blowing cold and as hard as it will. he told me that i have missing vents and need to run new ducts. how do i go about doing this?
Ductwork is behind the dash assembly, so they may mean that these have deteriorated and need to be replaced. Vents should be obvious if they are missing as they are in clear sight. These parts were all long ago discontinued by GM, so your options are salvage yard or possibly fabrication on the ductwork itself. Some of the vents, but not all, are available aftermarket. I'm not aware of any aftermarket duct parts though.
DrShock
Thanks for the reply. Be another project taking everything apart but what’s not to ‘project’ with a GM. have a good day man
Where can I buy the old transitier parts
There's a link in the description
This does not apply to 95s?
Same transistors and procedure applies, but has a difference circuit board layout so the video will not directly match those older ones. I mention in the video description about this.
Does anyone know of the brown wire that controls the ac mine gets hot and I think that’s what blowing out the controls?
The transistor I cover in this video is connected to the light green wire that exits the firewall and into the cycling switch on the accumulator, before routing onto other parts of the circuit to the compressor. To blow this transistor, a short on that green power wire to ground is usually required, sinking too much current and overloading the transistor. It can just be a momentary short, such as worn insulation from vibration on the harness. The transistor would blow out within a few seconds.
I have a 1998 chevy z71 all my knows work but the buttons only light up when blower Is off when I turn it on they go off I think it's the resistors I know I spelled that wrong but o well hopefully someone sees this to give me any information
There's a bit more technical info in the video description that might help explain. This video covers a power transistor failure, which has a specific failure signature. But other transistors, and resistors, failing on the logic board could cause other symptoms.
I did this and it fixed everything except now when I push the AC button in it shifts the air flow to the floor and doesn’t even come out cold, I’m at a total loss, I’ve been though 4 control units and tried this on all 4 including an AC delco one and got the same result, except one of the dorman units keeps the airflow on the floor permanently, sos
There's a few other comment threads around where the power output of this transistor goes and some of PDF schematics posted. There's a green wire on the flat cable out of the dash control unit, that travels thru the firewall and under the hood as part of the AC circuit. When this transistor goes you'll no longer have voltage on this particular green signal wire. I'd check this circuit with a voltmeter to confirm you're looking at the right problem. If the transistor is not blown and this wire has a signal, then its not the cause of the symptoms. However, if it's continually blowing the transistor though, then you have a short in this wire under the hood somewhere sinking the current to ground.
@@DrShock Thanks for responding it seems I have some poking around to do but in more detail when I put the ac Delco unit in with the new transistor everything worked but when I hit the AC button I hear the compressor engage and it works for a second or two then the AC button light and recirc button light starts flickering and then the compressor disengages and the air flows to the floor, is it possible that the issue could be related to the VCM? Based off a schematic I’ve seen the circuit goes in and out of the VCM 4 times
That flickering is a sure sign of a short on that power line (green wire) heading out from the transistor to the underhood AC circuit. They can take along while to track down, but the ones I've come across are usually where the harness is next to a metal bracket or fitting where two decades or more of vibration have rubbed thru the wire loom and into the insulation causing a short to ground in that spot. They can be intermittent too, I've replaced a transistor only to have it fail a few days later but in _every_ such instance I traced it to a short in that green power feed circuit under the hood. If you didn't have the flickering indicator lights before it burned the transistor out again I would have suggested something else instead.
@@DrShock Hi again, thanks for your help with this, I finally found some time to get back to this and I’m wondering if you can tell me by word how the AC circuit goes or link me a schematic to follow so I know where to poke around to try to find this short, thank you.
@@nickbriggs7247 There's a few older comments in here and one or two have linked a PDF of the 1998 C/K service manual. That's what you'll need to track down to have the schematic for the A/C circuit. The 98 one is going to be spot on for 96 - 98 pickups and thru 99 SUVs. If you have something older that same website might have an older one as well. idk.
I have the same issue, but would anybody know the proper name of the green selecter switch for the that determines which way the vent is blowing. Please can anybody help!!
So jargon wise, if that's what you're asking, that switch sets the air blend position so you'll hear the device that it controls called a blend door actuator. Sometimes folks refer to it as a zone selector as well. But I guess either are accurate, air blend selection or zone selection.
Hello! I put a brand new ac control unit/panel and I worked for one day and the cold air would only come out of the floor vent even when I had the dial on the face vent. Strange though that in winter time the panel works fine. When I dial in the vents for floor the hot air comes out through the floor, same for defrost, etc. But as soon as I would push in the ac button to test it out, the cold air would come out of the vent for floor only. Last year I happen to turn on ac even though cold air was coming out from floor vent. Well as soon as I turned it on the whole electrical system went out! I had to pull my truck with my Pop's truck back to the shop. I pulled off the shroud. I moved the harness connection on the left and all the electrical came back on. I have not messed with it since then. We are now in summer and it gets very hot here. Do you have any suggestions on what I should troubleshoot. Also, I would have liked that you had shown the public on how to test those bad transistors. I do not know much on electrics. Anyways, thank you for your video!
I think you would find, for this particular videos scope, that you have a short circuit somewhere in your wiring harness. Can't speak to the whole vehicle outage, as any short like that should have blown one or more fuses. But short to ground you do have, at least one. The power transformer in the control module is blowing because of a short in the circuit on the green wire coming out of the harness into the pressure switch located on the AC accumulator. From there you will have to follow the harness circuit to other switches and eventually the powertrain control module (or engine control module depending on the vehicle). The circuit varies between diesel and gasoline vehicles so a service manual is a must. I don't show testing those transistors because it's not a best practice to put them back, mylar circuit boards are not intended to be repaired like this. GM intended you to throw it away and buy a new one. So to minimize damage just install new transistors always, they are cheap. If you have the symptoms described in the video description, and only those symptoms, it's unlikely to be anything else but the transformer getting burned out. I would say you have more than this, as you experienced a larger electrical outage which would not be possible just from the problem in this video.
Mine was fine till I started the truck then it blew instantly
Can I send u mine for repair
Sorry no, I'm not a business.
Okay one day my AC and air condition motor no medium high switch work blower stop so I'm like okay what happened so I turn the knob back on and off and the blower change back on next couple of days it stopped working again I replace the relay switch still not working somebody talk to me please
If the problem is just some of the blower motor settings for AC stopped working, I'd suspect the selector switch. Not sure what you mean by _relay switch_ but I'm referring to what I go over in this other video - ruclips.net/video/Gl5_CEJdu4o/видео.html
You have no volume or audio
anyone know where i could get the ac harness ?
Not sure which harness you're referring to, but the least expensive option I would recommend is a you pull it type of salvage yard. Like LKQ.
it's the harness that is connected behind the hvac that you unplug to swap out the old hvac with a new/used one
Definitely wanna go salvage yard on that, cheapest route best fit. If there's an LKQ yard in your state that's where I'd go, that's a you pull it yard.
Whats a good brand name one to replace them with?
There are alot of makes, but newer more likely to be ON Semi or Vishay. Its a very common component from many suppliers. Small quantity eBay may end up being cheaper but Mouser.com is another option.
@@DrShock I saw some claiming to be motorola mpsa56 quantity of five item number 191131370944. How do i know these are really motorola?
Small parts like this use symbols, for a Motorola it would be a stylized "M".