How to Properly Diagnose a Failed TXV

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.
Read all the tech tips, take the quizzes, and find our handy calculators at www.hvacrschool.com/

[@petalumapapi]

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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[@samuelcuen4049]

BILLY ORR! You're the fucking man, bro!!!! You explain in my language. Keep it simple, realistic terms and terminology. Good looking homie

[@billni3952]

How to know is good fully refrigerant charged walking box freezer and cooler

[@b1conis]

Very good instructor. I have 45 years experience and 20 of that with Carrier and York. I’m still learning.

[@tonang33]

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.

[@kurtschaefflerakaclaudio4853]

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...

[@robertwojtowicz933]

You getting too long-winded with your explanation’s

[@mrc6032]

This guy is a great instructor. I don't really have that gift. So i appreciate anyone who can instruct/teach/facilitate

[@channelcatchaser9426]

Probably one of the best HVAC channels KZbin

[@bhutehole]

calling the TXV a constant superheat valve is a good trick for remembering what it does

[@greentea111]

THis is by far the best explained txv operation and fail operation ive seen yet... THank you for the very good lesson

[@YuShudNoe]

Completely agree!!! 💯

[@charlesdegaulle6465]

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.

[@Niveous23]

or a crawlspace....

[@QSSCEO]

Great video! Spot on!! The TXV has got to be the most misunderstood component of the trade.

[@craigspicer4296]

This has been a great Lesson and reminder about how to do the job better on properly diagnosing the TXV.

[@derrickseidenberg8105]

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.

[@padilla7019]

Watch this video a couple of times and makes me feel good to get this knowledge about txv

[@sterlingarcher46]

If only they taught me this well ... Fantastic class , sir , I wish I'd had my training with you guys 👍

[@seandardis9409]

Excellent Brian ! You can explain the workings of refrigeration parts in an easy to understand way .

[@mrV1et]

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 .

[@harvindersingharora3845]

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.

[@atinderpalsingh2817]

hello harvinder sir

[@harvindersingharora3845]

@@atinderpalsingh2817 Hi 👋

[@atinderpalsingh2817]

harvinder sir I need your guidance

[@harvindersingharora3845]

@@atinderpalsingh2817 mail me on [e-mail]

[@Sctronic209]

I like the explanation of the bulb being the opening force.👍

[@Stuart68505]

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.

[@adamz4345]

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..

[@billcamp8183]

Great, great class this instructor is an asset to the hvac trade. Good job.

[@itsnotfar]

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

[@benswafford8608]

I learned a lot from this video that I can use everyday. You are a HVAC wizard.

[@Bluecollarworkingman]

This is solid information. Presented and spoken well. Awesome.

[@vernroach3413]

Most excellent and informative video with an excellent instructor.....Thank you Testo.

[@Rodzilla408]

Good video I'll be watching this one a few more times.

[@MrGarcon98]

he is a very fast talker LOL

[@Imwright720]

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.

[@armandorodriguez6447]

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

[@billymonis8978]

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!

[@garycox1459]

Exactly. Tech knowledge good. Experience is key

[@mikefreedom5612]

Head pressure 0psig?

[@ryanjordan6144]

Billy Monis your over charged! That’s why it won’t pump down. Txv is not your problem

[@jskipperddg80]

@@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!

[@jeffreykubiak5126]

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!

[@brs4389]

flawless articulation of details

[@LongTrout]

Been doing service since 87....Love the vids....It is making me a better tech and helps me hone my skills....Thanks.

[@alejandromata825]

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!

[@chriscooley906]

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.

[@carlosportillo8863]

Very nicely explained Bryan. Thanks

[@dergadergaful]

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

[@chuckdearruda6271]

Great video! Thanks Bryan!

[@baylifehvac991]

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

[@jericosha2842]

great comment, thank you

[@USA-GreedyMenOfNoIntegrity]

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.

[@ernestorodriguez2711]

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.

[@poopathyraaja9949]

Awesome video 👍. Such a valuable information.

[@kenshofalco8326]

That was an excellent presentation.

[@nicaman96]

Thanks for a great class

[@trebrehenuf]

Learned more in 30 minutes watching than 2 years working with journeyman.

[@chrismesser7051]

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

[@Noverificationneeded]

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.

[@FlyEaglesFly19111]

The best techs have made the most mistakes.. they learned from them and made themselves better.

[@hvacae6904]

Exactly...

[@amantek3545]

VERY good explanation keep up the good work

[@austinisfullpleasedontmove653]

Mr. Orr here is what one would call an Hvac God. Love this dude and he has helped me through many a quandary.

[@Froggin87]

Absolutely great explanation thank you for that

[@chadbrown4918]

Cheers. Good job Brian.

[@beardowns8050]

Good stuff man.Thanks! 👍🏼

[@mrod72785]

Thanks Bryan, good stuff.

[@tribenitribhowan3638]

Explain very well, I learned a lot 👍

[@alexaderreyes5945]

Very interesting class it really helped me a lot on my Jobs thank you God bless you brother

[@markbeiser]

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.

[@vnesmuonnam]

Great lecture for TXV

[@donnierobertson3088]

Great job and video like always

[@OldePhart]

That was outstanding instruction. Well done.

[@HVACS]

thanks!

[@j.r.1223]

Great instructor!

[@bryanharayda1975]

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!

[@rastagrastag7784]

Great information.. well explained thank you👍👍👍👍👍👍

[@TheSixStringGuy]

Great lesson, thank you sir!

[@winkhvac62]

Excellent training!!

[@soloch69]

Great video like always 🙏🏻

[@jimmyclause847]

So educative and classified lecture..

[@BartSimpson-nr1dy]

I really miss this instrumental intro to your videos. Please consider using this tune in future videos. Great instructions on diagnosing a failed TXV

[@Stuart68505]

Very helpful information thank you

[@foreverendeavors6210]

Priceless information 👌

[@ssantoro36]

As a tech, I love these videos.

[@passandscore_]

Great video!

[@armandoacevedo932]

Thanks .excellent videos 👍👍👍

[@UNITEDHVACSYSTEMS]

Nice videos... Can understand how txv works and fails

[@UNITEDHVACSYSTEMS]

Please like to my channel also kzbin.info/door/VGxieHOcnRHZqMyC8ZrWtw

[@garycox1459]

Txv is pure gut feeling. I change out 9 every summer

[@deonnarine4363]

Great job sir , from Trinidad and tobago. Deon's air conditioning services here

[@boolve]

Good talk. It did exploded my head.

[@jspilly82]

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.

[@MrGarcon98]

our teacher who had at the time little over 35 years in the trade told us that 3 degrees in HVAC is close enough and dont sweat it too too much ,,,,just cool that house LOL ,,,,specially in miami /ftlaud / etc southern fl,,,nice show

[@VMac-eg7fb]

Excellent training, super informative, thank you.

[@adambarrett3296]

Thanks for the lesson teach

[@iskenderbytyqi]

you are the best master in my country. Republic of Kosova. Thanks for all.😇

[@ramchillarege1658]

Very good. Thank you.

[@Lemonpepperclub]

i should be taking notes!!!

[@felipeballi7679]

very cool video

[@ronyben-nachum7803]

Thank you very much for the wonderful explanation. Rony - from Israel

[@OGRH]

I feel really smart KZbin 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!

[@HoodHandyman]

great video

[@vanhap]

Very informative

[@billyk5107]

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

[@yisroelsones4552]

Professional and precise and very detailed

[@sethmeistergee]

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.

[@OcRefrig]

good vid.

[@hailthesuccubus5764]

Love the videos! Thank you for these!

[@jonathancastillo8235]

WOW this guy is very good

[@edjovi3677]

love this ch great job ed leak master plumbing in ct

[@nickdaggitt5079]

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.

[@juangerena3]

Straight cool and piston the best never had any problem

[@blancoazcracker365]

pistons,99% trouble free

[@brs4389]

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.

[@jericosha2842]

So was the indoor temperature of the suction line more normal and the temperature of the outdoor line really low?

[@maness2112]

I am never 100% sure when I condemn a Txv. It still feels like I'm guessing. One of my least favorite diagnoses.

[@tonymckay9031]

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.

[@mohamedkhan5207]

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.

[@SuperWingman69]

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.

[@ryanjordan6144]

marty maness replace the txv and ll drier and you can’t go wrong.

[@harpoon_bakery162]

i have a piston on my system, what's better Txv or piston. Should i be worried because i have a piston?

[@972958]

Tysm for your wisdom

[@HVACS]

You are so welcome

[@rodgraff1782]

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

[@andreagate542]

Thank you for this wonderful video.... I understand everything you explain in this video minus one factor. When you have a moment can you kindly explain why your DeltaT will go up when you have a bad TXV. Many thanks

[@jericosha2842]

If the TXV is underfeeding, there will be a noticable drop in pressure in the indoor coil. This will cause the coil to significantly drop in temperature. The air being pulled across will lose a lot more heat because of the colder than normal coil. This is what gives you a higher delta T.

[@farshadfaridmehr7271]

fantastic

[@josemarieantepasado5267]

Good day. If i may ask, i currently have a problem on an R22, 50 TR system with high superheat but with about normal suction pressure of 65psi. I've also observed that hissing sound you mentioned on the TXV and solenoid valve side. I am confused if this could be a case of a faulty TXV since my suction pressure isn't that low. I hope for your kind advice. Thank you.