Lost A/C on my 99 Savana 5.0 cargo van. No clutch movement unless I jump pressure switch. Thinking I might just be low on refrigerant I purchased a gauge set to evaluate system pressures and such before adding some... but neither hookup screws down far enough to actuate the Schrader valve /other(ball-valve?) on the service ports, thus getting no reading on either gauge. Does GM require a special adapter or ??? New to this stuff. Thanks. ****UPDATE**** Disregard above....gauge set appears to be working now. I had an old recharge hose and a new can of 134, I attempted to put can into system hoping to get clutch to engage. Unfortunately seal blew out(old hose)and lost some 134 in the process, but apparently enough got into the system to get the clutch to engage, though only for a short periods of time. I then borrowed a (good) hose from a neighbor and installed a second can. Fortunately no leaks this time and the clutch appears to engage longer now(though not long enough)and vehicle has "some" cooling. I hooked up my gauge set and am reading 61psi on the low side and 90-100psi(clutch off/on)on the high side with outside temps around 80 and humidity around 70%. The low side however is NOT dropping when clutch is engaged. Downloaded a chart that read low pressure side should be 40-50 and high side 175-210 at temp. Assuming my (cheap) gauge set is somewhat accurate, that shows(what I've read) is a potential problem with the compressor with the low side reading too high/not dropping when clutch is engaged. Should I leave gauge set on to see if pressures equalize, is there another issue(bad compressor/other), or could the 134/pressure still be to low as to not allow for accurate/normal pressure reading? The sticker says this vehicle takes 3lb.(48oz.)of 134a.