TXV Stuck Closed

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Old 05-30-16, 05:45 PM
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TXV Stuck Closed

I'll start by saying this is an automotive AC system. If The admins wish, they can move it to the auto forum. This is an older R12 converted several years ago to R134. It always worked but not great, there was a leak in a schrader valve that I only realized and fixed recently. The trouble started after I had to disconnect the evap to replace the heater coil. When I did this job I decided to replace the TXV since I had it open, changed the dryer at the same time. I decided to charge it with R152 at the time and it worked great. Recently with the warm weather, no cooling. I think I found the leaky O ring and vacuumed down and recharged. It worked freezing cold the first day 33 at the center vent. Next day no cooling. Static pressure 70-80 high side, 0 low side. When I started the AC the low side pulled negative pressure. Pulled the evap box out, changed the TXV, vac down and recharge R152. The TXV was completely closed, I couldn't blow air through it at all but it was clean inside when I took it apart, just clean oil inside. Second new TXV worked great the first day, next day same story. 0 static pressure on low side, 70-80 high side. BTW, when it was blowing warm air, something in the evap box was getting really cold because a lot of condensate was dripping out. I haven't pulled the second TXV out yet but I suspect I will find it stuck closed. Any ideas? Maybe the R152 is too cold for the system? Would that permanently jamb a new TXV shut? Next time I charge I will be using R134.
 
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Old 05-30-16, 07:14 PM
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I moved your thread to the automotive section. In the home A/C forum... system charging is not discussed as an EPA tech is required to handle that refrigerant. Auto A/C is treated differently.

I'm not familiar with R152 but I did read a tech write up where it's supposed to be as cold as R12. That would tell me that possibly you have a freezing issue with the valve. You said you replaced the drier. You said you pulled a vacuum. Did you pull it long enough ? Did you flush the system out with nitrogen first ?
Quite possible there is some moisture hiding out in the system.
 
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Old 05-30-16, 07:50 PM
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I pulled it down to 29.5 for a good hour or more, let it sit for 1/2 hr and pulled it down another 45 min or so. No nitrogen, I don't have that equipment. What I don't understand is why the TXV stays completely closed when the AC is off or even after it is removed. Will a freeze up cause permanent damage to the valve?
 
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