How to understand 60's/70's/80's GM blower motor circuits
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- Опубликовано: 6 янв 2025
- These are all essentially the same with manual controls. Common problems such as no blower or only working on certain speeds can be easily repaired once you understand how the different devices operate.
Pretty amazing this video was posted 8 years ago and is still helping people out. Thanks, got my AC going again after this video.
Thanks... hearing you explain it helped me figure out how the high blow relay needs to be wired. I am replacing the old tin relay with a modern Bosch relay.
For anyone else who needs it:
85- ground
86- orange wire from resistor
87- battery voltage (20a fused, 12g minimum)
87a- blue wire from resistor
30- blower motor
Clear videos like this are changing the game. They bring wrenching to the people and open up the possibilities they have for vehicle choice without being at the mercy of dealers and shops. I knew all the info in this one but only because years ago when I had my dash apart for other reasons, I had a close look at the blower circuits while they were exposed. (Simply cleaning the terminals at that time made it run smoother, too.) So this video saved many people from having to tear apart their dash or pay someone hundreds just to fix a couple of wires. You can also look at original GM schematics, but that still takes way more time than simply watching this video! First you gotta find one, and even if you have the official shop manual, well, go get some coffee and sit down at a table because it calls for a lot of page flipping and bookmarking. And that's before you finally find the schematic you need and then have to mentally translate wtf they're talking about. All while you're itching to be out there with wrench in hand like you expected.
9 year old video. Thanks a TON, exactly what I needed
Brother I have a 77 Corvette and couldnt find ANYTHING to explain this system as clearly as you did... from so called EXPERTS! Bless you... YOU have solved MY problem! Salute
9 years later, video is still helpful - you are right - this is the same sytem on my 85 Camaro and my 79 Caddy. My Caddy keeps blowing those relays.
Best wiring description of any videos I have seen. Helped me to find the black (ground) wire to the hi speed fan relay was not grounded. Thanks!!
I have had college professors who could not explain their subject matter as well as you have done here. I'm going to call you Doctor fix it. Outstanding video explaining how this circuit for A/C works. im going to subscribe to you channel. Thanks a lot.
This was an incredibly useful video, thank you mate!
I'm glad.
Well you just kicked stupid out the window and brought back common sense.
Thanks for sharing your knowledge Fort Worth Texas appreciate you.
Blessings and more blessings to you and your family
Video is perfectly explained in terms I can understand, I replaced the resistor and blew it again putting my fan on high, so I replaced the motor and still don’t have high. Looks like I need to check the relay. So glad I found this video
Even though this video is 8 years old, it helped me to finally understand that the blower motor was designed to be on low with the key on. It runs on LOW all the time.. OMG,!the hours I put into my 1979 GMC Caballero or El Camino, same basic layout. Now I can button her up and move on. Thank you very much. E The Swiss Army Knife
Right, gm refers to that as flow-through ventilation or astro ventilation
Your a really good teacher, very well explained and understandable.
Thanks! It's not easy to explain this stuff sometimes.
Thanks for this. The fan on my ‘79 GMC only runs on low and I’m getting ready to start digging into it. This will save me a lot of time.
Thank you for this video. My wife's 1981 Pontiac Bonneville's AC just stopped blowing on high speed today, now we know where to start looking.
I have a 79 Camaro (Rally Sport) and the dash switch had burnt out and broken up internally so i finally found original switch ($50 for the models with A/C) but the pigtail plug from dash wiring is a little boogered where it got hot. Keep loosing connection on med. 1 and med. 2 at my switch. If i can ever find a NOS pigtail for it I will be aces then LoL. Ive considered cutting it off and just splicing on female slide disconnects but for the sake of simplicity and originality i haven’t done it yet. Thanks for being good at what you do, because of your videos my quadrajet that left me on the side of the road is now 100% rebuilt and running like a champ! All 4 barrels are doing exactly what their suppose to do. Once again, thank you thank you thank you! Ive also put many quadrajet haters in their place because of what you have taught me LoL.
Kris Denton what happened when the switch went bad? My blazer is blowing the fuse right after I turn those key, my best guess is the switch but I guess that why I’m here
I'll get into the 68 today using your vid as a guide. Answered so many questions! Thank you!!
I just wanted to say thanks for taking the time to post these informational videos. I'm refurbishing my GMC G35 vandura at the moment and your clips are really helpful in understanding the basic principals of my vehicle. You have a very good way of describing things. So thanks!
Thank you so much! I"m working on my 1980 Silverado that has a bunch of wires cut and missing. The manual does not show this detail - you saved me!
Great job explaining. My 79 TA is blowing the fuse under the dash when turned to high. I will be ordering a new relay I think.
Did a new Relay fix blowing the fuse issue? Mine on high pops the fuse both in a new and the old relay. I’m thinking the orange wire might be connecting metal somewhere between the switch and relay,
Finally a video for vintage factory a/c.
Thank you.
I’ve been searching for a helpful video on this subject for a long time!
Great video! Thanks!! How does the blower get power to always blow on low when the schematic shows the temp and a/c selector switches have a open on the input power from the fuse box when both are in the off (all the way left) position?
One other thing about those relays is that they also sometimes stay stuck on the on position with the blower running on max with the key out of the ignition and the heater controls on off quick fix is to tap the top of the relay till the contacs inside disconnect. Happen to me a couple of times with new and old relays in that same GM setup. Could save you alot of headaches trying to figure out because it did for me.
Thanks for explaining this. I’m working on an 80 and the wiring has been hacked and butchered. The fan doesn’t try to work at all. This helps a ton.
The AC/Heater blower motor seems to operate on all speeds in my 1979 Trans Am but it does not seem to push enough air out of the vents. I have a new AC system but not enough comes out of the vents. I took all the heater ductwork out and made sure it was sealed properly and that did nothing. New blower motor also.
I got my vacuum fixed to control the doors as it was only blowing cold winter air. However the blower stopped working and when I checked the fuse it is good. I jumped 12 volts from the battery and motor comes on. Wondering is maybe the fan speed switch is bad and how exactly do I troubleshoot it
so on the fender mounted bus bar does that have constant 12 v to relay ?
Just a little tip, as far as electrical theory, voltage doesn't actually flow-it's only the current that flows (ie, electrons moving through the wire). Voltage is basically the difference in "potential" between the positive (12V) and ground (0v), and the amount of current that flows depends on the difference in voltage between the two points (12 volt difference), and the amount of resistance in the circuit (resistors, wires, and anything else in the circuit that resists the flow of the electrons). So basically, 12 volts doesn't "come in" to the motor, as voltage doesn't travel-it's only the current that flows (hence the rating of fuses in amps-which is a measure of the amount of current that the circuit can handle, before the wire would melt or catch fire). Hope that helps! Thanks for your videos, they're very informative, and I appreciate the friendly style as well
Thanks for the tip!
WhoSaidTyler You're welcome! And thanks again for the videos!!
My blower runs with the key on position with the car off the switches are in the off position. Had replaced the blower motor, blower resistor & and relay. I got a new fan speed selector switch, but I have not installed it yet. This is on 76 firebird
i have a 76 k10, i can hear blower motor running when truck is not running,. after starting and trying to turn fan speed up it does not go faster, no speed change. I dont know how to test ,where to start? Also my accumilater doesnt have that switch? on left side of it ,is that needed? thanks
Hello Tyler, I have a 79 K10 and I have done an AC delete. When I bought the truck, nothing worked and I put a new blower in. Using a Power Prob 3, I can turn the blower when powering the #2 connector slot (Black w/white strip) x2 wire on the ac/heat selector switch. When the connector is inserted into the switch, there is no operating from Off-Defrost. #3 wire is green and #5 is Brown and they have no continuity. #2 does. Could I be missing a wire here or bad switch? Does this selector switch need a power source? Thanks
From the 12v distribution block,there is a inline fuse on the orange wire that leads to the relay. What size amp should thay fuse be?
I put in an ac delete panel on my 1971 Monte Carlo. I cut a hole in new panel and took resistor off ac unit and installed . The dark blue wire is not connected and the tab where it goes is broken off. The fan doesn’t work at all. I’ve been working on this for days . Any thoughts? I can hear a springy noise coming from relay ( the first metal box) when I flip selector switch to high but yeah it doesn’t work at all now.
Do u have a wiring diagram? Most of the wiring has been cut on the 74 gmc c15 we just picked up.
Been trying to find it via Google
Great explanation. When I turn the heat on in my 65 LeSabre, the blower kicks on only when I put into gear and start driving. Sometimes it'll come right on, sometimes cool sometimes worm. Today I noticed the orange wire coming off the resistor circuit attached to airbox getting so hot it lights up, melting the insulation. This only happens when the heat is on. Any idea where I should start? Thanks
Hey brother I am having issues with my fuses popping when I turn my switch from the off position. I’ve put on a new relay and resistor as well as a new switch control. I’ve gotten it to run intermittently for about twenty minutes and then that fuse will go. I’ve disconnected the resistor all together and it’s working for now but the darn thing is new so I’m hoping that it’s bad out the box. How would I know if it is my issue causing fuses to blow?
A very good explaination of how this circuit all works. My problem is I have a 69 chevelle same wiring diagrahm with air cond. When I go down the road with the air on after about a half hour or so give or take 30 minutes it blows the fuse. Air is working fine which is drawing about 5 amps when running when I check the purple wire with the fan on high speed and the air on it will spike to about 18 amps. Could it be the resister or relay thats causing the blown fuse.
unplug the blower does fuse still blow?
When I turn the controls on the dash onto heat or air and go back outside to check my blower motor the negative and the hot are registering hot can you help me with this problem
My blower only work on Hi. Low and Medium doesn't work. So I replaced that resister. But it didn't fix the problem.Then I replaced the A/C fan blower switch, that wasn't there problem either. Any other ides?
1980 GMC keeps popping the fuse switching on high new relay and resistor any suggestions thank you
My 78 is the same way, my switches aren't working but it's idling at one speed, I put new ground a new blower and the switch worked before but it's a new blower but won't turn on high, how did you fix yours?
Great video. I’ve got sudden loss of power on all fan speeds as well as no compressor kick on nor electric fans (wired them to come on when AC is triggered). Checked fuses. How common is control module failure?
I have 12v at my relay the relay is testing good the speed control switch inside has no voltage my fan works the resistors are good the blue wire from the resistor to the relay is good still not working I’m gonna try replacing the relay and see if that fixes it but I’m unsure if that doesn’t do it
Having an issue with my 84, if I take a wire and connect the battery to the fan it runs just fine but soon as I connect the wiring harness with the fan to the relay it doesn’t come on at any speed. I took a multimeter and I’m getting 13 volts to the red wire on the harness. The fuse is fine as well. I’ve done tried 2 brand new relays and still can’t get anything going. I cleaned the grounds as well.
Do u know the name of that purple plug
I bought an 85 caprice and mice chewed it up.. ?
Ok can i use any other truck blower motor for my 85 monte carlo ...is there any other blower motor campatable
If it has a bypass for all non-max blower power inputs until the coil is energized, I can assume it's an SPDT style relay?
Blower motor in my 74 c10 is not working on any speed I have 12 volts at the plug for the motor but the motor is still not working neither the old or the new motor I tried work at all.... Any thoughts?
Check the ground wire that goes to the motor. There are actually two wires going to it. A purple one like he mentioned in the video, and a black wire which gets grounded to the fan case. Make sure the paint is scraped from where the ground is connected
I have a 1970 El Camino; the fan blower motor switch keeps getting hot and burning out upon occasion; I've replace the fan switch 3 times; I don't know why it gets hot; do you have a solution? Also, I recently purchased a new fan switch; and blower motor. I can change out the switch easily enough; but honestly, I don't know where the blower motor is located; I think it may be under the dash somewhere because when it was on, I could heard it running, but the design underneath the dash below the glove box is strange to me; nothing is obvious like it would be seeing it on the fire wall on a C10 truck.. If you have a video of how to replace the blower motor on a 70 El Camino, I would sure appreciate that help. Thank you.
I got power to the resistor and to the relay but nothing in the two wires going to the blower motor on a 79 trans am, so blower isnt working on any speed
Where is the fuse located in the fusebox for the blower motor?
good explanation. I was able to find the wrong size fuze in the panel and then the wire wasn't connected to to the blower motor.
Thanks for the great video explaining how the system works. I just purchased a 1974 chevy stepside a few months ago and slowly doing some repairs. When I turned on the heater and defroster, the system appears to work but there is a loud whine. Since the electricle seem to be working, I am wondering if best to start by checking the blower motor? Do you have any videos of actually pulling that out and cleaning? Or replacing? Thank you
I have 1988 S-10 fan only blows on high. I change resistor did not help. Where do I go now?
Thanks for this great video. I was replacing the speakers in my 1975 Cadillac Deville so I had to take the dashboard apart. After putting it back together, I realized the blower motor isn't working anymore when I put the key in. It only works on defrost now. What would cause such a situation? I'm guessing I messed up something when putting the dash back together, but I can't seem to figure it out.
How wire it if you want to delete the ac and put just heater box there. We eliminated the ac box with just heat, so where do we wire or get a resistor so we can have hi med and low speed on the motor. Where would we place the resistor since it gets hot. Thanks
I would get a non-AC box and harness from a similar vehicle, it should fix you up
Excellent explanation.. fixed my high speed blower after watching this ..thx
Hey I’ve got a 1977 impala wagon. I need to test the ac pump so I want to force it to engage. But I can’t find a way to jump it to come on because there’s no pressure switch that I can see. I’d appreciate any help. Thanks
My junction block has nothing attached to it. Curious if I need to connect to it. What’s connected opposite the orange wire. Also, where is the ground for blower motor
The ground usually connects to the firewall at one end and directly to one of the blower motor mounting screws at the other. Junction block on the firewall should have a fused(or fusible link) 12v+ feed wire connected. The large red high speed wire for the blower motor relay also connects to the junction block for its power.
Best explanation on the wiring, Thank you!
Why is the ac pump on the driver side? Mine have always been on the passenger side. Am I tripping?
Anyone know anything about blower motors with two wires going to the top? They plug into two similar lookin metal tabs. I know one is for power i have no clue what the orher wire is for. The vehicle this blower is in is an 81 Malibu
Thanks for the detailed explanation. I have a question. The brown power wire at the connector behind the control switch in the dash gets extremely hot when running through the blower resistor at the 3 lower speeds.. It doesn't get hot when it's on high. The wire stays cool when it bypasses the resistor on full speed. It's only when running through the resistor that the problem occurs. I replaced the resistor and the wire still gets extremely hot. The air conditioning doesn't work because of a leak at the compressor. Any help would be greatly appreciated.
My brother's truck keeps blowing the fuse when the blower is set to high. Trying to figure out what it can be. We have replaced almost the whole system. We are leaning that the wire itself must be the problem. It has a new resistor, new relay, new blower motor and we tried a new switch on the climate control. Yep we just started throwing parts at it because the previous owner had it all tore apart.
Thank you for such an informative video on the heater blower motor circuit! I have a question... I have a 78 chevy c10 with AC. the blower runs on low, m1, m2, but not on High. I have replaced the blower motor, relay, and resistor. I am also getting power to the relay from the switch. Any help would be appreciated Thanks again
It will be standard test procedure from here on. You simply trace power from it's source to it's destination and determine where it "stops". At this point I would focus on the wiring to and from the relay. The relay has load in, load out, a trigger from the switch and a ground. Check carefully.
@@TylersNeighborhoodGarage Thank you for all your help and reply!!! Will try to make some of these tests tomorrow. Thanks for taking time to assist with these issues! I really appreciate it.
Question so I got my fan working in my 86 custom cruiser on all speeds but high when I go to high I can hear the relay click but I get nothing could that be that relay or should I dig deeper
You should check the large red wire on the relay connector for 12v+. It should usually be connected to the junction block on the firewall. If it doesn't have 12v+ at the relay connector, it doesn't matter if the relay works or not, the fan won't run, because that's where it gets its high speed power
I've unplugged the selector switch and made jumper wire to bypass the switch so I could hear the motor run on high but all I hear is the relay clicking. Do I have a bad selector switch and motor. Use to run on just low then not sure when but just stopped working all together. Any help would be appreciated thanks
Which fuse it? Is it one of those metal case type fuses? My blower used to work on low, but now not at all even after replacing switch. Thinking it may be resistor.
My relay is clicking when i unplug it but the switch ic not sending any power to the blower on 1985 iroc camaro
Can you show were the vacuum line goes to
On my 85 C10, blower fans work, heat works, but AC won’t come on. How do I diagnose what to fix?
Hi stinky smoke came out of AC vent and the fan for ac quit. The fan works on heat still. Any ideas? Good video .1986 G20 van
Ok, my resistor is on a 1973 grand am. My high and low won’t blow. 2 and 3 blow fine. My resistor has 5 prongs, not 4. How does that work?
Hey I have a 79 trans am and I don’t have a Compressor on mine and I heard that your fan will never stop running unless you have it and so mine works but it never stops running unless you turn of your ignition so I was wonder if it’s normal.
it probably has flow-through ventilation like the truck do. Essentially, that means the fan runs on low all the time. Nothing to worry about. Compressor has nothing to do with it.
@@TylersNeighborhoodGarage thanks man! But hey at least I got heat now!
I have a 1984 with a none working blower .. Blower works with a direct power to it .But not working at all hook up with factory set up Fuse still good what would the next step .. with out replace everything . There is 12 volt at block on the fire wall ..
I checked the circuit and jumped it and the fan ran on high sped so i replaced the switch and it ran for a few seconds and it stopped so what happened?
Is it possible to hook up a 3 speed/heater only control assembly (3 tabs on the back of the fan selector) to this same box in the bay (4 tabs on the resistor). I guess the only thing I'm bypassing is the hi-speed selection in the relay?
Please help need answers! I have a 79 Chevy Scottsdale C20 has AC I replace the blower motor I replace the resister ,the relay I’ve replaced the switch panel on the dashboard and what happens is when I turn the AC on and I turned it to Max AC it’ll come on sometimes and then sometimes The generator light will come on and it won’t blow at all and I switch it to vent fan comes on I’ve replaced fuses wiggled the fuse box and sometimes it come on and sometimes it won’t so I do not know what’s going on if you can help me I would be forever grateful
Great video, helped a lot. Working on my 77 c-20 and the whole ac system is getting a rebuild from scratch so this is helpful.
That 77 c20 is worth a lot now. Any money you put into it now is well worth it. Auto metal direct can help out with rusted out body panels., hoods and doors.
Hey I hooked mine up I can’t find where to plug the wire with thick red cord I seen where to bolt it
I need some help. My k20 81 has two selector switches one for my heater And one for ac. The ac one doesn’t work at all I found a burned fuse I replaced it and it turned on for a bit. Then blew. I disconnected the compresser wire and the fan doesn’t turn on at all I can turn the clutch and the pully spin
Awesome! I have been trying to get my heater to work for a while now and I’m so glad you had a great vid to explain it!
You have a teaching gift, glad you are using it productively
Where does the power to the A/C Pressure Switch come from.
Thank you, question, I have exactly the same truck, and I was assembling the relay wiring, the 10g wire that goes to the block junction box is not hooked up and fan works fine, any toughs on this? I know that this relay needs power but seems like it’s getting it from somewhere else
My issue is I can't find the fuse. I want to start there cuz I don't read voltage on blower plug.
I have a 66 lemans that the blower motor doesn't blow air at all, No matter what position the switch is. The switch, or a relay? It doesn't appear to have blown fuse.
I have a 79 c10 like yours fan works on low only I just got the truck two days ago and it’s cold, think you can help me out please?
What about the green and light green wires? Where do does go?
Hi !thanks for this video.
My blow fan motor did work few months ago. But Heater core was dead. I change the heater core.
But now blow fan motor do not work.
I change for new resistance /relay/ control switch (in the Dashboard). But still not works
I put 12v battery connections directly to blow fan motor and it works
I dont understand. Can you help me please ?
Think of it this way- one end of the entire circuit is connected to the battery, in a roundabout way. The other end is connected to the motor. Along the way it passes through a fuse box, ignition switch, relay and a blower switch. If it doesn't go whoosh when you flip the switch, then somewhere the path is broken. You just have to find it.
Great video. On my 78 Cadillac coupe, the AC blows only in low even if the setting is on High. But I noticed under the hood, the brown wire that's connected to the blower is disconnected and has a red jumper wire connected to the connector terminal that is on I guess it's the resistor, there is only 3 wires leading into the connector. I've never disconnected it or made an attempt to see what it does if I remove the red jumper wire and reconnect the brown wire in fear that it would fry it and then I'll have no more AC. Now I've used the heat and works on high setting but blows low? 🤷♂️ thoughts?
thank you for blessing the world with this useful video.
Hi, I have a quick question about my blower motor not running on high. When I switch it to high it clicks at the relay but doesn't do anything. I tried 2 new relays but still doing the same. Also I replaced the temperature control unit with a new one. Could you please give me your advice. It does work on first 3 speeds. Thanks for your help!
My hodge-podged 79 GM unit...mounted on a Dodge M500 Frame, all driven w/ 440/A727 drive train, all in a 1980 Fleetwood RV, E-25 Package equipped,, well it came as a _"Some Assembly Required"_ deal ;)
My issue is the 7 "Teats" coming out the back and why in the world can't I find a diagram for proper what vacuum line to what teat placement anywhere....found a few for the typical round pattern, which also usually is accompanied with these mounted on a pre-fit plastic ring as to plug all vacuum lines in @ once ;)
and even more concerning is that there's only 4 vacuum lines (all 1 color, BLACK) to put on said teat's, and should I block off the remaining 3 teats....or start looking for different vacuum depend devices with no lines on them?. I did sort out which was my suck source by of course, starting the engine... guessing the other 3 here, one is for defrost flap other is for fresh/recircl and 3rd for heater core??? But that'll be the easy part, I just don't know which line goes to which teat, I wasn't fortunate enough to have one of those factory form factored pre-set rings that let ya plug em all in @ once. This one also doesn't have said _"Teats"_ arranged in a circular pattern, these are all just splayed across the back of unit, no stamped numbers, letters, nothing
Haven't had a free minute to back trace these yet, got one now, and yep....raining blood out there currently
Par for the Course...
You'll get there.
@@TylersNeighborhoodGarage Believe I am getting there...Thanks to this video, I finally know what this relay under hood is for now. So your telling me that this relay is just actuated when you set the blower switch to High???
Much appreciated Tyler
@@thecentralscrutinizer5105 Yes. The reason is that the amperage load on High is enough that it would risk overheating the switch.
@@TylersNeighborhoodGarage I've learned something today, Much appreciated sir
I have no power at any speeds where should I start ? 1984 gmc new blower motor
I might have missed it in the video but how do I know what’s wrong when the high don’t come on and it still stays blowing low??
And would you know why my heater stay on even if I turn my ac on?? I have a 1977 Pontiac Grand Lemans
someone told me i could reemove my AC belt for better mileage and horsepower, since the A/C doesnt work anyway. Could this cause problems>>> would you advise doing this or not doing it? Could it effect engine timing chain?
I answered your question on the other video, but, a 1982 GMC Vandura is never going to have good fuel mileage or good horsepower. I would direct your tinkering efforts elsewhere.
Hello, I have an 87 Chevrolet Silverado, ac compressor not getting any power. Checked fuse, all the fan speeds work. I put a wire directly from the battery to the compressor and it works just fine (Did that just to see if it was working) however, when I turn the Ac on it doesn't get any power to the compressor. Any idea
There is a low=pressure cut-out switch which kills power to the compressor if the refrigerant charge is too low. I'd check and add gas if necessary and it should work.
@@TylersNeighborhoodGarage will do, appreciate it. Thank you.
I just swapped out the that cut out or cycling switch and the compressor didn't kick in. Going to add the 134 and see what happens.
Thanks for your video. My blower hasn't worked in 10 years. Finally decided to get it working. This helped. But know I'm having a vacuum issue my blend doors dont work. all my hoses ( check valves if needed) from the reservoir to the manifold are gone. Do you have a video on this.
Any idea on why I would be getting power to all the wires on the resistor at once?