I have a '91 Volvo 740 wagon with the Volvo 134a retrofit (not Interdynamics) done by a dealer, long before I acquired it. It worked great for a few full days a few weeks ago in 90+ deg temps; a couple of days later I turned it on and got ambient air. The compressor cycled, although quickly. I put a gauge on it while it idled; compressor off, it ran at 40psi, compressor on, it dropped to 20 psi. Static was about 85psi. Today (weeks later), I got some time and thought I'd try some more troubleshooting, but now the compressor won't even switch on... I tried to charge it, but it won't take a charge, I'm guessing because it needs a running compressor to do so... I know on some GM cars you have to jump compressor at the relay to get the charge started; do I need to do the same here?