How to Properly Diagnose a Failed TXV
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- Опубликовано: 21 сен 2024
- Bryan gives a masterclass to Kalos Techs on why TXV/TEV valves are misdiagnosed, how to properly diagnose a failed TXV, and how thermostatic expansion valves work.
TXVs are designed to maintain constant superheat, and many people suspect TXV issues when the suction pressure is low. When technicians see low suction pressure, many of them may add charge and then realize that the TXV throttles down to maintain constant superheat. So, they condemn the TXV even though it's working as it should because they simply don't understand how the TXV works.
TXVs generally have an external equalizer, which supplies a closing force to the TXV. The spring also supplies a closing force, but the sensing bulb applies an opening force. The size of the TXV's orifice depends on the combination of the opening and closing forces. There is a fixed amount of refrigerant inside the sensing bulb, so the hotter the bulb, the more the refrigerant expands. The more the refrigerant expands, the more opening force it will exert on the TXV. When the bulb doesn't have enough (or any) refrigerant, it can't exert enough force on the valve to open it. However, you may be able to replace the powerhead without condemning the entire TXV.
The TXV needs a full line of liquid coming into the valve for it to work properly, so we need to check the subcooling or look at a sight glass (in the case of refrigeration). We can get vapor in the liquid line from restrictions or excessively long lines.
TXVs may also have an inlet screen, which can become restricted and prevent the proper amount of refrigerant from reaching the valve. The TXV also needs a proper pressure drop (about 100 PSI); without that pressure drop, the TXV can't do its job properly.
When the suction pressure is low, the technician should take the subcooling and superheat inside and outside. The goal is to look for the temperature differences between the inside and outside measurements. If the differences are drastic, then there could be a restriction somewhere (often in the line drier or an airflow restriction).
If suction pressures are low and the temperatures are close to freezing, the next step is to take the remaining measurements of your 5 Pillars (superheat, subcooling, delta T, suction pressure, and head pressure). Use those to diagnose the problem; the superheat at the evaporator coil should be 6-14 degrees, and it's usually not productive to condemn the TXV over a couple of degrees due to the possible inaccuracy of our tools. Instead, it's more likely that you have an airflow problem.
However, if the outdoor superheat is 27 degrees and the indoor superheat is 23 degrees, then you'll have to check for restrictions. If you don't have any restrictions (which may cause low head pressure) and have sufficient subcooling and pressure drop, then it would be safe to condemn the TXV.
When taking measurements, make sure your test instruments are calibrated and work properly. Otherwise, you could misdiagnose a TXV problem.
Moisture, carbon, and other forms of contamination can lead to inlet screen restrictions and possibly even premature TXV failure. If the superheat is high, you can temporarily open the valve more by increasing the suction pressure by placing the bulb somewhere else. NEVER open the valve more if you have low superheat! If you have low superheat, try to see how well the bulb is connected to the suction line; for the TXV to work properly, the bulb needs to be strapped in a way that makes it have good contact with the suction line. In cases where the bulb needs to be insulated, make sure it is insulated.
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I've been watching videos of you classes you're very informative I really appreciate the information you guys are awesome
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BILLY ORR! You're the fucking man, bro!!!! You explain in my language. Keep it simple, realistic terms and terminology. Good looking homie
How to know is good fully refrigerant charged walking box freezer and cooler
Very good instructor. I have 45 years experience and 20 of that with Carrier and York. I’m still learning.
I watch Brian to sharpen my understanding of refrigeration as it relates to automotive air conditioning.
What a great teacher and orator. Thank you Brian for doing what you do...
You getting too long-winded with your explanation’s
Probably one of the best HVAC channels RUclips
I am not a tech but I love learning about many things. Having a good A/C tech is important. More importantly someone who is trustworthy. I will continue to watch his videos. Thank you for your knowledge.
This guy is a great instructor. I don't really have that gift. So i appreciate anyone who can instruct/teach/facilitate
THis is by far the best explained txv operation and fail operation ive seen yet... THank you for the very good lesson
Completely agree!!! 💯
calling the TXV a constant superheat valve is a good trick for remembering what it does
This has been a great Lesson and reminder about how to do the job better on properly diagnosing the TXV.
Watch this video a couple of times and makes me feel good to get this knowledge about txv
My teacher of the day! I have unlearned and re-learned a few things from your video.
Thank you for the wonderful session. You added a fourth angle to my triangle.
hello harvinder sir
@@atinderpalsingh2817 Hi 👋
harvinder sir I need your guidance
@@atinderpalsingh2817 mail me on technoengineershyd@gmail.com
I subscribed to this channel because as a restaurant owner , I’ve been taken advantage of 4-6 times over the course of 4 years between my walk in cooler and freezer , ice maker and main ac unit. I now carry my own gauges and temp probes to sadly check their work. I video and picture log all my equipment to make sure they don’t “ break “ something they should be doing . I constantly ask the tech questions and their approach and results they are aiming for to verify. I collect their answers and back research info from your channel . Thanks for these videos. They are less inclined to pull a scam on me now .
If only they taught me this well ... Fantastic class , sir , I wish I'd had my training with you guys 👍
23:00
I FEEL VINDICATED.
I should save this video for every customer who “just wanted” their 20 year-old, never maintained attic AC in their 120 year old house “fixed” instead of replaced.
or a crawlspace....
We often use your videos for our weekly training with our techs. This one was great! Thank you again for what you do for the industry.
Excellent Brian ! You can explain the workings of refrigeration parts in an easy to understand way .
Thanks- lots of insights that are new to me. The review of the complete diagnosing procedure was also helpful. One service manager told that first thing he would do was to put his amp probe on outdoors to get an idea about how much refrigerant charge is in the system and to see if the compressor was running. I used that idea to check a new refrigerator at my apartment which was icing up constantly. The store technicians came and told me that it was improperly sloped and not draining & that’s why it was freezing. How ever it continued to freeze up. It was only drawing about 2 amps instead of the rated 6 amps under full load. They eventually replaced that new unit with another new refrigerator.
I don’t understand why it makes a loud clicking noise every time the compressor starts up that is coming from inside the cabinet and not down at the compressor.
I like the explanation of the bulb being the opening force.👍
Great video! Spot on!! The TXV has got to be the most misunderstood component of the trade.
Add air into the mix and you got yourself a long day
Great, great class this instructor is an asset to the hvac trade. Good job.
Good video I'll be watching this one a few more times.
he is a very fast talker LOL
Been doing service since 87....Love the vids....It is making me a better tech and helps me hone my skills....Thanks.
I just replaced a txv yesterday. It had low suction pressure about 50 psig ( R22) SH was about 45 deg. high head pressure at 400 this was after the day shift added 22. SC way high. Took some out until suction pressure started going down. then pumped unit down, couldn't get low side below 40 psig before the compressors internal bypass opened. The head pressure got all the way down to almost 0 psig. the coil was freezing up. Put the new one in and was getting the perfect cycle. Good feeling!
Exactly. Tech knowledge good. Experience is key
Head pressure 0psig?
Billy Monis your over charged! That’s why it won’t pump down. Txv is not your problem
@@ryanjordan6144 if the TXV has been starving the compressor long enough it will go out on high heat when pumping it down. Doesn’t mean overcharged!
I learned a lot from this video that I can use everyday. You are a HVAC wizard.
My friend is taking night classes in south Florida. The instructors first language isn’t English. Poor kid can understand half of what the teacher says. I wish he had you. You are an excellent instructor.
Awesome video. From my experience with txv is I always see the outlet of the valve with frost build up and my subcool doesn’t make since or is way to high. I know so many installers who braze with out nitrogen and years down the road this is then end result. Honestly on all my service calls are maintenance I always check for dirty indoor coils , filters, ductwork and blower wheels that will cause low air flow. God bless
great comment, thank you
I purged with nitrogen on all of the systems I’ve installed in the last 20 years. I still have lots of TXV failures. They are junk, engineering in the USA and poorly made in China. Greedy corporations don’t have any problem paying their suits millions.
Great information. I'm new to this stuff, so it was lots of food for my brain. You explained it in a way I could easily understand. Thank you
Learned more in 30 minutes watching than 2 years working with journeyman.
sorry to hear that man you must of worked with some bad guys, i feel the opposite iv learned way more in the field to the point where i dont get much from alot of his videos, not bragging but alot of his material is introduction to stuff and very basic
trebrehenuf .......you’ll learn even more and much faster when you put hands-on. And more still when you’re on your own, with nobody watching you. Also, this is a trade that is very cerebral and you’ll constantly learn. Like the instructor said, even a seasoned tech can misdiagnose.
The best techs have made the most mistakes.. they learned from them and made themselves better.
Exactly...
I’ve changed power heads before only to find that the valve was restricted at the body, I’d rather just change the whole thing if time and conditions permit. Good class!
We have a Lennox unit that takes 29lbs of refrigerant and it worked perfectly fine in second stage but we were getting the typical readings of a txv valve failure, low suction. I traced the line to the condenser and saw a hell of a mess of a braising job. Traced the TXV and saw that someone had melted the copper with the torch and the pipe was pinched to the point of no airflow when tested with nitrogen. Pointed it out to the Linux tech who recommended we change the solenoid first. We changed the TXV and braised everything. Pressure tested it over the weekend checked for leaks and recharged it. Works like a charm
This is solid information. Presented and spoken well. Awesome.
A note on your statement at the end about what happens if a valve core is left in the port the equalizer line connect so.
On many valves, there is not a perfect seal around the rods the diaphragm pushes on to drive the valve open, so refrigerant inside the valve can leak through and push the valve closed.
It will be higher pressure than the refrigerant in the evaporator coil, and has no place to go, so will force the valve too far closed.
I ran into it a few times back when AS/Trane switched to providing aluminum replacement coils for their air handlers with copper coils.
The coils come with no TXV, so you have to field install it, and people were not pulling the valve core out of the port.
After starting the system up, the valve would start off forced wide open, flooding the coil, then slowly close down until the superheat was way too high.
Most excellent and informative video with an excellent instructor.....Thank you Testo.
Really good lesson or over view. I’m recommending this lesson to the green hvac bros coming into our co. This will make a good tech out of the average tech filter changers and part changers
Mr. Orr here is what one would call an Hvac God. Love this dude and he has helped me through many a quandary.
Nice videos...
Can understand how txv works and fails
Please like to my channel also
ruclips.net/channel/UCVGxieHOcnRHZqMyC8ZrWtw
Pure gold Bryan, So technical you really drive home the facts, I love the videos and podcasts great reminders to strive for greatness and never assume without having all the facts Thanks again.
Very informative, I've also been a last resort to change a txv,but over the years have had a few that were the TXV valve was bad..
Constant super heat valve is accurate. Easiest way to check valve is measure superheat and subcool when close to or at temp. Always measure suction temp closest to TXV sensor bulb to calculate superheat. TXV, EXV, DTC valves are fun!
I really miss this instrumental intro to your videos. Please consider using this tune in future videos.
Great instructions on diagnosing a failed TXV
I am currently pretty hungover and I can’t sleep. But I just watched your video and I understood all of the information. Wow. Such a great video, I had to subscribe. I will watch again when not hungover to make sure I retain everything. Thanks so much. Great job.
you are the best master in my country. Republic of Kosova. Thanks for all.😇
As a tech, I love these videos.
flawless articulation of details
REALLY appreciate your explanation about how a restriction can actually show lower high side pressure-- as a refrigeration guy I see that all the time on LG fridges with partial cap tube restrictions.
Thank you I’m working on a unit now that I have to check all this because when I got there it was frozen so I told him I would be back the next day to hook up everything again and run it properly and see what’s going on before I condemn anything
I am never 100% sure when I condemn a Txv. It still feels like I'm guessing. One of my least favorite diagnoses.
Same. Some guys check pressures, SH, SC. Then, put txv bulb in hot water, and recheck those pressures,(suction should go up, feeding more refrigerant) you could also do ice water and txv should feed less and have lower suction. But others check pressures, SH,SC, but they even add refrigerant and see that suction deadends, again to Bryan's point, neither of these are practical. More so checking more things like discharge gas superheat off compressor. I've learned about having bad txv when changing a rusted drier, then added refrigerant charge to unit charging chart then the suction hit a deadend and wouldn't rise anymore upon adding refrigerant, the headpressure would also stack if much more refrigerant is added after that deadend. Not the best way to know, why I've been trying to find better approach.
Maximus Decimus Meridius lies, kink liquid line or clogged filter drier will increase head pressure along with liquid saturation temp which will show a subcool within range, or dirty condenser coil will raise liquid pressure and show subcool within range. Don’t feed false information to newbie techs bud.
Brian, thank you for your time and effort in making great content for us all to learn from. I work on commuter trains . We have 2 , 8 ton package units. In each unit There are 4 TXV's feeding 2 evaporator coils. There is liquid line valve and a branch circuit off the liquid line that incorporates a modulation valve, that when energized provides "Full cooling" capacity through feeding all 4 TXV's. Partial cooling capacity is accomplished by de-energizing the modulation valve and feeding only 2 TXV's . Question, Would I have to operate these units in full cooling to properly calculate SH? I've never seen a system with multiple TXV's like this before. There are no manifold gauge connections, only transducers and NTC thermistors mounted on the liquid and suction lines. We use R-407C refrigerant.
marty maness replace the txv and ll drier and you can’t go wrong.
i have a piston on my system, what's better Txv or piston. Should i be worried because i have a piston?
Txv is pure gut feeling. I change out 9 every summer
Great lecture for TXV
on a traulsen two door commercial refrigerator can the body of the txv sit externally? outside the evaporator housing? as long and the bulb is inside?
That was an excellent presentation.
Bryan great video as always, but ive always wondered and asked what refrigerant is used inside of a sensing bulb. It would make sense to me that the bulb would have a small amount of liquid refrigerant of whatever the system uses that its rated for but i have never been able to find documentation or get a definitive answer. Just a question ive had for 10 plus years.
some aircons have check (one way) valves that will give some of the same symptoms as a bad txv. if you are thourough in the diagnosis it will become obvious but always use both hi and lo gauges and check system temps in lots of places. its been rare to have a check valve fail but they can give you a real hard time if your not aware of them.
I always questioned the reasoning behind "clocking the bulb" so it doesn't sense the liquid. Umm, it's at the outlet of the evaporator on a copper tube. Right?
What are signs that tell whether the screen just infront of the txv is plugged? Is their enough space to measure or even see temp differences?
It’s a good idea to install a 1/4” flare T at the connection for the equalizer line at the evaporator. The extra port can be used to get a pressure measurement for the actual evaporator pressure at the tail coil, where the bulb is located. This is the proper place to read suction pressure when calculating evaporator superheat
Thanks Bryan great video technician going possible back into field after 14 years in house maintenance. Probably watch again.Beer can cold days are long over. Thanks got your app on my phone!
I got a tricky one. How do you troubleshoot/ adjust a circuit with multiple txv’s ?
Wasn't sure where to ask this question, but I am looking for an electronic expansion valve with a controller that will allow me to run suction pressure below zero PSI. I can't find a controller that won't fault out when trying to run Ultra load temperatures like -80F. I have to put the controller in manual mode then I can dial the electronic expansion valve to exactly what is needed whereas a TXV loses a lot of its ability to meter at these ultra-low temperatures. BTW your channel is in first place tie with the engineering mindset Channel. That's a pretty big compliment
Thanks for the lesson teach
Thank you very much for the wonderful explanation. Rony - from Israel
I feel really smart RUclips is recommending this to me and I have no idea what the hell this guy is talking about. But everything that breaks gets fixed in my house so I guess one day this video will come in handy!
Good talk. It did exploded my head.
Quick question and apologies for lack of understanding, my HVAC unit is ~10 years old, last year around winter time, we lost charge, and compressor was not working etc. Our tech after hours of testing decided it is this valve. Hence replaced it. Since then, we hear a squeaky/ chirping mechanical sound at diffrent times, and can never pinpoint the location.. the system works fine, the noise is horrible? They came to check it twice, and found no issue. Slightly low refrigerant, filled it, and the noise was not different! Any idea is appreciated
The video is very informative for technicians who knows all this stuff already.
For me who just starting to learn about hvac is a headache listening 10 words in a second .
Cutting the video clips to make a shorter video doesn't help me.
Have you tried playing it at .5 or even .25 speed?
Very interesting class it really helped me a lot on my Jobs thank you God bless you brother
What if the txv is clogged and you can hear gurgling? That would be causing low pressure lock out right. Change the txv at that point?
Great Video but i do have some questions. So my question is 21:35. right there you have a high superheat of 27 degrees. From there you say "then you can condemn the txv". how at that moment did you figure low charge still may not still be a factor ?
Brian so instead of running up and down from attic to condenser unit every time you warm or cool the TXV valve bulb what about taking advantage of the Fieldpiece or Testo probes along with the Measure Quick app and watch what you pressure's and temperatures are doing. Saves alot of running around for those that have them or frees up a second person. Also can probably use an infrared terminal immature on the TXV. Just a thought 🤔
WOW this guy is very good
one time I suspected a kink and the line temp difference between ID and OD was like 15-20 degrees. I searched and sure enough the lineset was bent where it exited the wall cavity.
So was the indoor temperature of the suction line more normal and the temperature of the outdoor line really low?
Very nicely explained Bryan. Thanks
You can also cover the condensing fan or unplug it and watch the head pressure go up and your suction pressure should maintain and not move at all this is a good txv if your suction and liquid line increase bad TXV
I found a jumped O-ring keep the needle closed on a 30 ton once, unfortunately tried ordering and changing the power head first.
How would you measure the superheat inside I’m confuse
Excellent training!!
Awesome video 👍. Such a valuable information.
Feel like I missed something.without gauge pressure , how can you measure a suction line temp outside at 50 and say saturation temp is 40, when checking suction line temp inside it’s 47 and say it’s 7 degrees superheat? Why couldn’t it be 37?
I live in SE Texas and I have been having problems with my central ac.I have a friend that is an ac guy and he put gauges on it and said it is alittle low on refrigerant but not enough to make it quit cooling all together. I think the condensor is the one that came with the house back in 1977 but in the attic, its not quite as old. The compressor runs and I have airflow. Might it be the txv? I've heard that I can cover the condenser to stop the airflow and I should not see the gauges move when the air heats up. If the txv is had, the gauges will not move. Does this sound right?
Great video. Add a hot gas bypass system with liquid quenching to this and troubleshooting gets even more interesting. Then throw in flooded condenser and it's a party.
where do you place the temp sencors to measure superheat and subcooling inside
Best tool for manipulating a TXV bulb is a ‘hot hands’ warmer. You don’t have to disturb the factory insulated connection.
Just came across your video .
Maybe you can answer this .
410A Ac system it 4 ton .
My low side 156 at the gauge and 14 deg SH
The high side is 287 with 1.4 deg SC
Suction line temp 68 degrees. I’m thinking it’s the txv . I shut down the high side and the compressor pumped down .I’m at a loss
i should be taking notes!!!
I pretty sure this is a class for HVACR technicians Continue Education, but not a class for newbies like me. Will come back after I have certain HVAC knowledge
Check out their RUclips home page and look under the 'refrigeration basics' category - lots of great stuff for newbies!
Visit back often. Once you get more experience you can picture what Brian’s talking about 😄
Great information.. well explained thank you👍👍👍👍👍👍
Common issue with installers over heating the suction line on units while brazing and burning up the temperature bulb and causing the txv to remain closed. Causing compressor to pull a suction side vacuum.
if you had a wet rag wrapped around the bulb it should be fine.
I’ve been installing high efficiency equipment for 25 years, purging with nitrogen and keeping TXV’s cool while brazing. I’ve had plenty of failures between 4-8 years. Chinese sourced, poor US engineering.
@@p.imprint your right or thermal paste and simple remove the bulb. Its a lack of training in proper technics from my experience.
Are you taking the indoor superheat and sub cooling using the pressures at the condensing unit?
22 year old Trane R22 system. XE1200 with a TXV on coil. (13 Seer) Condenser coil very clean. Evap coil can't be observed, without cutting case. (Probably dirty, after 22 years.) Outdoor temp 90 degrees. Super Heat is 49. Sub Cooling is 17. (Coil paperwork calls for 16 nominal sub cooling.) Liquid line / head is 210 psi and suction line is 49 psi. Obviously freezes up and looses ability to cool below 74'. Trane factory dryer / filter on condenser does not reflect difference in temps across. Liquid pressure line temp outdoor is 85' indoor is 82'. 25' delta T. Sounds like TXV to me. I will test the TXV bulb by dipping in cooll to hot water and watch the low pressure this week. Feedback welcome!
My man on Hvac Pro Talk for sure lol
How do you check superheat and subcool inside?
Professional and precise and very detailed
How to know is good fully refrigerant charged for walking box freezer and cooler
Explain very well, I learned a lot 👍
In easy words, restriction means: a mass flow of refrigerant is flowing inside the pipes very little although you have enough refrigerant level in the system.
Great video like always 🙏🏻
Every TXV I have had a problem with was gummed up. Just take it apart and clean it with a brass wire brush and nonclorinated brake parts cleaner. Reassemble evac and dump the charge back in. I replace the filter dryer too when I opened the lineset.
Absolutely great explanation thank you for that
that was a lot of information in a short amount of time.....but well done!
Priceless information 👌