Bryan explains why and how to adjust a TXV and what to consider before doing it.

A TXV maintains a constant superheat value at the evaporator outlet, and it needs proper refrigerant flow to do its job right. Some of them have screens in the inlet, and those screens may provide a restriction that prevents a TXV from doing its job.

TXVs also require sufficient liquid pressure to meter the refrigerant into the evaporator; the TXV drops the refrigerant pressure before it enters the evaporator. We have a target range of evaporator temperatures and pressures because we don’t want the evaporator temperature to be too low in A/C and medium-temp refrigeration applications.

Before adjusting a TXV, consider checking for restrictions that resulted from contamination. Check to make sure the sensing bulb has been properly strapped to the suction line. The bulb should be fastened snugly to the line; if it’s too loose, then it can’t do its job properly. If the line is insulated, then the bulb may be insulated WITH the suction line.

Adjusting the TXV won’t directly change the pressure; it will affect the superheat. So, adjusting the TXV is NOT the way to deal with low suction pressure. You only adjust a TXV to make it reach the target superheat. Also, see if you’re measuring superheat inside or outside; the outside superheat may give you an inaccurate reading due to the likelihood of higher ambient temperatures.

Not all expansion valves are adjustable. You can tell if a TXV is adjustable by looking to see if they have a nut at the bottom. That nut covers an adjustable stem, which affects the position of the spring on the inside. (The spring pressure is a closing force that opposes the bulb’s pressure, an opening force.) A non-adjustable TXV would have a flat bottom instead.

If you want to decrease the superheat and feed more refrigerant into the evaporator coil, you would turn the stem counterclockwise to loosen it. If you want to feed less refrigerant into the coil and increase the superheat, you’ll tighten the stem and turn it clockwise. It’s a good practice to adjust a valve in half-turn increments so that you don’t overcorrect the problem. Once you make an adjustment, let the system run for a little while to make sure you’re meeting your superheat target.

Allow the system to run for at least 15 minutes before adjusting the valve; there needs to be sufficient head pressure for you to get a good idea of the TXV’s status. You’ll also want to measure the superheat before you think about adjusting the TXV.

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49 thoughts on “Why and How to Adjust a TXV / TEV

  1. Johnny B says:

    lol, good luck finding a txv that you can fit a knuckle buster wrench on to adjust. Your going to be using a refrigerant wrench that ratchets, so you need to be very conscious on your rotation of the stem. Also, this can be a brutal job, try adjusting one inside a freezer thats below zero, where your waiting 15 minutes at a time each adjustment.

  2. Jared Jeanotte says:

    ok i just learned this the hard way, 9:00 min in, i was working on a walk in and reading the temp/ psi at the condensing unit, so i think i bungled the super heat. i had i lot of bubbles inside the sight glass a more experienced technician said just add more 404a till the bibles stop and than just a bit more. i did. bit, but now i don't real know if its a leak or broken txv? i should have done a leak check but hind sight is 20/20 i guess.

  3. Andy Peek says:

    One trick I use is to clamp the phial on to the suction pipe with a cable tie to hold it in place whilst fitting the phial clamp.
    Very usefull when underneath a milk vat with limited room to work. And allways insulate the phial with foam tape.
    Its no different down here in New Zealand.

  4. bug Den says:

    just a little about dirt ,,,i ran into so many contractors about brazing with nitro ,,,,they say oh i never had problems or call back because i did not use nitro ,,,,,then it becomes an arguement ,,,,and i am talking about guys with years of experience ! ,,,its all about the money first , get my house cool for as low as you can ,,,lol i am old school i was a certified welder with over 30years experience when i decided to go to school for HVAC . every tech tries to impress the other LOL ,,,,,just saying this school is good stuff for all of us ,,,,i am retired but love to learn more

  5. Karl-Alfred Römer says:

    What i am always wondering: Is such a TXV fast enough? How many seconds does it take between change of temperature of the refrigeration fluid behind the evaporator and change of temperature and pressure in the sensing-bulb? I guess, that can take half a minute or more.

  6. Ed Lauren says:

    Man, if I understand correctly, you are teaching HVAC students as a part of your activities. So, I wish I had a mentor like you years back when I was at the beginning of my way. You have a great talent to put the whole story short, clear and easy to follow. Your students are lucky to have such a great teacher.

  7. Irving R. Lucas says:

    I have r507 chiller operating at 1 to 4degC . What is reco. Superheat..I test it once, measure it in the evaporator, suct.temp is -1C then suction pressure is 50psi..according to chart 50psi is -10C . So my SH is this right?

  8. Mary Burnham Cataldo says:

    You say adjusts a TXV to get correct super heat what about adjusting it for Sub cooling? I installed a Danfoss tr6 into a system that had a piston orifice and now I'm having trouble charging to 10 deg Sub Cool. I'm at 7-8 degs and cant get it any better. Oh and it not responding to charge because I've gone for low to over and still cant make the ideal S/C

  9. disonesto says:

    Will adjusting txv let me lower the temp? Coldest I can get so far on my car is 45F. And would like to drop it more. My txv has a spring adjustment. I also tried switching from r134a to r152a

  10. mattdamonism says:

    I'm really late watching this video but I just had a TXV unit installed that calls for 7-9 degrees of superheat. The subcool is dead on in the high 8s, but the superheat is at 24. I checked ductwork and there are no leaks that I could find other than a couple of tape joints that had a very minute amount of air coming out, I taped them up. But my delta T is still at 16, I feel like something is wrong with this install. Any ideas?

  11. Nicky says:

    I just had my AC unit serviced and the guy refilled the refrigerant since it was completely empty. Now my AC unit is really struggling to pump cold air – i was thinking of giving this valve a half turn to allow more refrigerant through – is it possible it was reinstalled "too closed"?

  12. Zipper Dingo says:

    Thanks Brian, question please, I always have hard times brazing these short necked TXVs, I cannot easily roll them well with a wet rag, I use a strong neutral flame to make it fast but, the rag tip gets burned carbonizing the joint and the valve over heats rapidly, any suggestions? Thanks

  13. Xx TJI says:

    Your explanations suck! You hop all over the place back and forth instead of systematically explaining the process as a sequence of operation! No wonder it takes years to get qualified, your confusing the simplicity of the process!

  14. Kenneth Lobo says:

    Great video.Thanks for imparting and sharing your expertise with us. A request could U do a video on selecting a TXV for a particular evaporator coil what parameters would I need to consider.

  15. Pennconst101 says:

    It’s also important to note that superheat is pretty important to the compressor. It’s important to know what your superheat is before it reaches the condenser because if the superheat is perfect at the evaporator but too high at the condenser then that can create an issue.

  16. MD Willington says:

    Just had a heat pump installed and have had the installer out 3x now with the A-coil completely frozen, saying it’s a bad expansion valve, I hear in this video how the smaller lines are “delicate”… Well, ours look like they just yarded the damn things out all haphazard, looks like total crap..,

  17. The Aleons says:

    My company keeps trying to use these thermal expansion valves on low temperature Chillers that we manufacture. They are anything but an constant superheat valve. The electronic expansion valve it's so much more Superior especially with variable heat loads. The problem I have is the electronic expansion valve controller wants to fault out if I run the suction pressure into a vacuum period or if I run my suction line temperature below – 59 degrees Fahrenheit. Then the controller wants to fault out and close the expansion valve completely. When I talk to an engineer at Sporlan he asked me how low do you want to go. I'm like negative 100 degrees Fahrenheit. He just laughed at me.

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