Why and How to Adjust a TXV / TEV

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.

Read all the tech tips, take the quizzes

[jeffbarrett]

HVAC IS AMAZING! I LOVE HVAC! just what is HVAC? doesn't matter CAUSE I LOVE

[edlauren]

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.

[manismello]

I really enjoyed this detailed presentation on the Expansion Valve!
This Video will go into my most valued folder as an accurate reference point!
Thank you much.

[shawnriddle]

Awesome video. Glad i watched. Found a 5 year old R22 4 ton split A/C system with a closed txv. Flat sensing bulb. I weighed the charge in and my suction and head were low. Ambient temp in the lower 70's. Need to go back when i have a good ambient to check the superheat and sub cooling. Parker said the valve comes set @ 10 degrees superheat.

[ralphchiappetta]

This video Presentation is very informative to all people working on AC Units around the Country. Thank You.

[AmericanFarmerHVAC]

Very informative. just saved my ass at a disaster of a job today. Got my superheat correct

[janibashamolla]

Thank u sir....
Dear sir. You explained in theory its 50% knowledge for us. Better if show me. Practically its 100% exalent for us sir.

[aircooledtx]

Very good explanation on adjustment. Best check airflow and superheat at evaporator. Also ^ TD . I have only adjusted valves in refrigeration units, walk-ins and freezer. Ole style Q body valves were much easier to adjust and maintain S.H. For the smart super techs, if you listen to Bryan Orr might learn a wealth of knowledge.

[kennetheldridge]

Great video, ,for the technician out there, ,take a black marker and mark the bottom of the TXV before you start adjusting so you know where you started, ,make half turns ! Left or right so you can see where your sub cooling is going up or down..I wish On the videos you would show how it works

[shanegreen]

Thanks so much for sharing your knowledge. 👍👍👍👍👍👍

[johnangeleri]

Thank you. Very thorough. I appreciate all the "filler words"... they added the detail that I wanted to know.

[kennethlobo]

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.

[OcRefrig]

Enjoyed the Podcast ! Works good to pass the time while doing the
dishes, also picking up a thing or two here & there. been doing
refrig . since 1981, also information on whats going on in the trade
sometimes. Thanks for making them.

[packjtw]

Excellent video Brian. One of the few viewed that explains a TXV in simple English.

[christopherhelvey]

Thanks for your superb explanation. Very helpful and I'll probably refer to it again. :-)

[Pennconst]

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.

[davidgagnon]

You Stepped WAAAAY Outside of Explaining ANY TXV Action within the 3:00 minute mark for ANY HVAC TECH of 1-2 years are just speaking to Yourself at that

[MrGarcon]

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 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 saying this school is good stuff for all of us, ,,,i am retired but love to learn more

[kinggenius]

good information! Thank you for making videos!

[leftright]

so essentially when adjusting superheat setting your going CCW or CW facing the bottom of the valve at the stem not facing the power head?