I was working on a walk-in cooler today with the journeyman that I am apprenticing under. The unit was not keeping temperature. The refrigerant was 134a. The unit had a TXV and a reciever. The sight glass was showing a full head of liquid. Suction 18, head 110. 45 degrees superheat at the compressor. The coil was clear and both evap fans were operating properly.
We attempted to adjust the TXV. It was a 1/3 ton Danfoss TXV. We spent about 2-3 hours trying to adjust it properly. It would temporarily begin to feed better as indicated by suction pressure and SH, but SH would then again rise suction pressure would drop...I believe that we were allowing adequate time for things to settle in on each adjustment (5-10mins) but it just would not seem to stay consistent.
In the end, we ended up changing out the TXV and this fixed the problem.
This took a long time to diagnose and then more time to change. I am wonderning if you would share some experience with me in regards to diagnosing TXV's? Because I don't know how to PROVE a faulty TXV in a time efficient manner. The entire time that we were tweaking the original TXV, I suspected that it was the problem, but I didn't know how to prove it. Even in the end, we just sort of conceded to the fact that "oh well, I guess it must be a bad TX valve". And I guess I'm just asking you guys if I can do better than that on my diagnosis?