I need the opinions of those more HVAC knowledgeable than I am: Since the pandemic kept us off the road for over a year, I find that the A/C no longer works (equipped with a Sanden compressor and Duracool, it had operated without attention for the previous 5 years or so).

A couple of days ago, I vacuumed the system down to near 30 in.HG. and left it sitting until today, when it was still at almost that level. Then I moved the vacuum hose to a fresh can of Duracool and opened the valves. The low-side and high-side gauges both immediately indicated ~95 psi. Then I started the engine and engaged the compressor. Neither gauge's needle even flickered! Repeated compressor clutch cycles yielded the same results: Click-clack of the compressor clutch and obvious rotation of the compressor shaft -- yet NO needle movements.

I took a brass hammer and rather strenuously rapped the compressor (on "hard parts") hoping I might shake something loose inside -- STILL no needle movement with clutch cycling.

My diagnosis is that I have one of 3 problems in the Sanden compressor: 1. A sheared shaft; 2. A valve stuck open; or, 3. a busted piston -- in that order of probablility. Does anyone, hopefully, have another/better idea? Maybe even one that won't require compressor replacement?

It's looking less and less like I'll really need A/C in the GMC this year, but I'd still like to get it working before I get still older and less able
to tinker, so Y'All's opinions will be greatly appreciated.

Ken H.