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Question DetailsAsked on 4/27/2017

is it possible that in AC unit would only lose Freon when running?

I had my AC system charged in October it set idle all winter and held pressure, when I started using it in the spring it only ran for about two weeks before it lost pressure. The technician charged the system to 600 psi with nitrogen , and found no leaks. Is it possible for a system only to lose pressure when it is running?

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2 Answers


Wow - 600 psi test on an R410a or similar high pressure unit might be OK for some units, but normally the nameplate rated test pressures I have seen is more like 150 psi for R-22 (Freon) units, and maybe 400 psi for R410a units. That is a LOT of pressure to put on the coils especially.

Certainly - in almost all systems (and probabluy all residential systems), when not running the pressure on the high side drops off, equalizing with the return (low pressure) side of the system, and the pressure also drops off as the system cools off. Depending on your system make and type of refrigerant gas, high side pressure can run commonly in the 100 to 250 psi range though some R410a unit for example get up to around 400 spi on hot days, and the low side from 10 to 100 psi - so when the unit is shut down the high side pressure may drop from about 100-250 psi to something much less than 100 psi.

So - if a leak is realted to pressure - like a leaking valve or fitting that only opens up enough to leak under high pressure, it might not leak noticeably when shut down. However, since he tested it to 600 psi, my question would be did he test the ENTIRE system at that pressure, or only part of it (maybe cutting out the coils).

Other possibility - that the compressor itself is leaking when it runs - probsably would have also leaked a bit when the test pressure was on it but maybe not noticeably, but say there is wear providing a leakage point in the compressor that is exposed only when running - that could cause a loss only when running.

I would guess either the pressure test was not held long enough, or time to go with a thermal IR or dye detection system to find the leak while operating normally.

Course the other question is HOW do you know it held pressure all through the winter - if you mean it worked in the spring, it could have been quite low on pressure and still worked in spring temps but then completed the leak off. Many systems have a fair reserve of refrigerant in the compressor and filter, so it might be the unit ran OK but maybe just working harder than it should have had to initially even though it was low on refrigerant, then continued leaking off and finally started behaving noticeably poorly as the refrigerant got low enough. That would be my guess as to what happened if you did not actually gage the pressure before spring startup.

Answered 3 years ago by LCD



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Answered 3 years ago by Member Services

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