AC pressure questions (finding a leak)

[Chebyshev]

I just replaced the AC compressor in my '89 325iX with a Four Season 57400. The car had previously been converted to R134a, but I don't know the details of that conversion. The Behr compressor that was on it was frozen.

I went to pull a vacuum on it and it won't hold a vacuum, so now I'm trying to find the leak and I don't really know what to look for. I put ~50psi of shop air in the low pressure side and sprayed soapy water on what is accessible from the engine bay, but didn't see any bubbles. I'm trying to avoid removing the front bumper and screwing around with the condenser if I can.

When I put pressure in both high and low sides, the high side quickly goes to around 80psi (my compressor is set at around 90) and stays there. The low side takes a bit to get to around 50psi and then drops back to zero after about 10-15 minutes. I was under the impression that the pressures should equalize since the high and low pressure sides are connected through the expansion valve and compressor. Should this take a long time? Does the fact that they aren't equalizing point to something for me to check on? Am I way off in my understanding of how this works?

[tomstin]

I am no AC expert but agree both sides should equalize without the compressor working. My guess is your expansion valve is clogged causing the difference in pressures. It maybe stuck so the high side holds. If that's true, then the low side would be leaking at the evaporator in the dash. And there is no easy way to test that without removing it.

When the first compressor went, there is no telling what junk may be in the system. I think the leak is only the beginning. I think you're going to end up pulling the evaporator and expansion valve, cleaning out the lines, new dryer, expansion valve and evaporator, seal it all up and cross your fingers.

Rob Siegel's book, "Just needs a recharge" is a great reference for us DIYers. It was very helpful when I rebuilt my AC system. Remember to insulate the expansion valve!

[Chebyshev]

I actually figured it out this morning:

I screwed up installing the high side service port on the top of the receiver-dryer (and used the wrong receiver-dryer as well), so I was just pressurizing the high side gauge hose, not actually opening the port to the system on the high side. Felt like an idiot.

I also found the leak - my condenser has a hole, so I guess I'm ripping the front bumper off.