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.
Check out an updated version of the video: https://www.youtube.com/watch?v=IPMIv-ro3kg
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HVAC IS AMAZING! I LOVE HVAC! just what is HVAC? doesn't matter CAUSE I LOVE IT!!!!!!
How many evx percentage is normal
Very informative. just saved my ass at a disaster of a job today. Got my superheat correct
Good explain sir
Just so you know I could not watch your video because I could not get past the dumb a** the d****ss CSV comment.
Im not sure why, but there;s a 2 minute delay before the video actually begins. It starts for a couple seconds then turns white-screen and restarts about 2 minutes in.. so your visual and what you're saying are way off. Just sayin..
Love your classes. Outside is subcool. Isn't it?
Very good advice to ADVICE guys
Your video is nothing but white space.
Hi great infromative video but the audio and video are way way out of sync 🙁
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.
Why do people say reducing superheat (smaller safety factor against liquid) uses more of the evaporator / is more energy efficient?
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..,
Without charging the gas, the pressure in the suction increases and the cooling decreases, why is this problem happening?
Great demo, thanks! 👍👍
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.
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.
Excellent video Brian. One of the few viewed that explains a TXV in simple English.
Nice video thanks! But 5 min would be enough. first half is water of time. I also want to know, whether R22 TxV can be adjusted to fit R410a
Plenty technician dont know bout this
is this a video about how the valve works or a troubleshooting video????
Yes a CSV makes complete sense and not those other misleading confusing names
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!
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
Very good detail explanation thank u
Brilliant