A/C update.. not so good

[treed2 at wsu.edu (T. Reed)]

Hi all,

I've spent a significant amount of time over the last few days getting my 
A/C put in and working. I changed the expansion valve, all the o-rings, 
the high/low side valve cores, and the receiver/dryer. Then I pulled a 
vacuum for about 45 minutes and charged the system with 3 cans of r134a 
(36 oz) and 4 oz of ester oil (I had a 3rd 2 oz can but the threads were 
stripped so I didn't use it.. I bought a replacement but haven't used it 
yet because of the high pressure explained below).

Actually bringing the system back to life was a piece of cake compared to 
re-installing it. It's been a while since I've fully taken apart the 
jungle of belts and tensioning brackets.. it's a real knuckle buster. I've 
got the cut up hands to show for it. It took me an evening just to get the 
compressor and condenser installed, and another evening to put the 
evaporator in the passenger compartment. The third day (Saturday) I pulled 
a vacuum and charged it.

Initial results were okay, but a little disappointing. I didn't get a 
chance to measure temperatures but they were maybe 15-20 degrees colder 
than outside (about 90F). After a while with recirculated air, I think 
it got down to about 25-30 degrees cooler than outside.

I drove about 30 miles with the A/C running to the store and back twice, 
then as I made a left down my street I felt the air through the vents 
suddenly get warmer and musty-er, and the A/C hasn't worked since.

When I got home from work tonight I checked the low pressure switch, 
expecting to find that the system had leaked empty.. but the switch was 
still closed. The compressor clutch wasn't clunking in to place when I put 
12V on it directly with the engine off.. but for some reason it would 
operate if the engine was running.

The compressor engages and runs, but I get not even a hint of cold air. I 
put my pressure gauge on the low side with the engine off (the high side 
r134a adapter won't work on the high side so I didn't hook the high side 
gauge up-- the adapter has the wrong thread) and the pressure needle 
pegged off the scale at somewhere from 350-400 psi. Yikes! It was the same 
with the engine running. During charging it was 'only' about 55 psi..

My first thought was that something must be plugged up. But the more I 
think about it, I don't understand this at all. The low side feeds the 
suction side of the compressor. If the system was plugged (e.g. at the 
expansion valve) it seems like the low side would be closer to a vacuum 
and the high side would be over-pressure. It's not possible to hook the 
compressor up backwards because the fittings are different sizes. The only 
way I can see there being high pressure at the low side port is if there 
was a clog between the suction port on the compressor and the low side 
port.. creating a vacuum at the suction port and building up pressure 
everywhere else.

The possibilities that come to mind are that the dessicant bag in the 
brand new receiver/drier could have ruptured and plugged something (but it 
would have to travel through the expansion valve to plug things further 
down the line), or the expansion valve could have been defective/plugged 
somehow (but again, this doesn't make sense given the high pressure on the 
low side), or the compressor could be self-destructing and put some debris 
in to the system. But again, I can't quite think of how these would cause 
this kind of failure.

Everything looked good going in.. I don't know what to do next. I just 
know it's supposed to be 106F tomorrow and rolling my windows down doesn't 
do much to cool things off here in AZ.

Any ideas?

-Toby