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AC stops working after 20-30 minutes- chase a leak or a clog?

hankthetank on Fri July 06, 2012 8:40 AM User is offline

Year: 1998
Make: vw
Model: jetta
Engine Size: 1.9 dies
Refrigerant Type: r134a
Ambient Temp: 90F
Pressure Low: 29
Pressure High: 225
Country of Origin: United States

i recently got a 1998 jetta tdi with 330k without working AC. I was suspicious of the high mile compressor so i swapped it with new orings, did a quick evacuation and recharged so I was getting 320psi high 38psi low and was happy with the performance. 5 days later it first stopped cooling, but only after running it for 20-30 minutes. If I wait another half an hour, it works again.
from inside i notice I hear a slight click coming from the dashboard (instrument cluster area) at the very moment it stops working. I'm assuming that is where the relay is located and it's just being shut off by the low pressure switch?
Today i put it back on gauges and saw that it's at 225psi/28psi while it's cycling (at idle) before it stops cycling. After resting for about 20 minutes the pressures settles back to about 100psi each and then it comes on again but not for long. I'm not sure where to start- to assume low charge and leak, or possible clog somewhere in the system? I sprayed soapy water all over the condenser and every underhood hose/pipe connection and couldn't find any evident leak. I didn't check the evaporator. I suppose my 10 minute evacuation could have possibly not boiled out all of the moisture and it's possibly icing up the expansion valve? I can't find an obvious leak, not sure if it even has a leak or a clog. If it's possibly clogged I'll replace the receiver, expansion valve and do another evacuation/recharge but I'd prefer to get some more info first. Can anybody offer insightful advise before ordering hardware?

joe_mn on Fri July 06, 2012 9:38 AM User is offline

did u replace it with new compressor? what brand? you say you swapped it.

mk378 on Fri July 06, 2012 9:39 AM User is offline

This is a variable compressor system, it should not "cycle off".

It's not a leak, because then it wouldn't start working again without being recharged.

I think you have an electrical control problem, especially considering it's a VW.

hankthetank on Sat July 07, 2012 7:00 PM User is offline

I didn't replace it with a new compressor. It was used out of another VW that the AC previously worked well. It was the exact same part number on the sanden unit as the original. In hindsight, I don't believe the original compressor was bad.

I was thinking that it could be a leak because I'm not seeing as pressures now as when i first charged it (and it had stayed on the entire time). It does still come on, but stays on for less time than it has previously.
I'm familiar with VW electrical gremlins, but this car is in good shape electrically, and has a pretty simple system so I'm pretty certain it's not an electrical issue.

could it be a sticking expansion valve?

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