I have successful experience repairing, recharging AC systems in vehicles, construction equipment and multi-point bus and limousine systems. I could really use some advice on this one. Thank you for your help.
The AC hasn't been working on the well-preserved 92 5.7 Silverado I received last year. The AC system seems to be stock and undamaged. The compressor did not run when AC was selected. AC indicator in heater display would come on and stay steady, but no compressor engagement and no cooling. I installed the gauge set and found only 10 psi in the system. I vacuumed the system for a couple of hours and it seemed to hold vacuum well. Refrigerant vapor added to low side raised both gauges to 60 psi. (correct expected tank pressure for ambient temp.) I expected the compressor to start as low-pressure switch minimum pressure was exceeded, but it did not start. I hot-wired the compressor clutch. It engaged properly and compressor ran smoothly and quietly, but did not lower the low-side pressure at all. No response or so slight I didn't see it. Revving engine to 2500 rpm surprisingly made no difference. I had only a few minutes to spend on it so disconnected and tried again two days later.
The second time I connected the gauges, the pressure was down slightly and there was small oil film around the compressor shaft seal area. I again hot-wired the compressor. This time the low side immediately dropped to 5-10 psi and I was able to charge system until low-side running pressure was 30-35 psi and reached 65-70 psi when I cycled the compressor off. There was slight, but noticeable, cooling happening at the air vents. After running for 30 minutes I connected the clutch to its wire harness plug and the compressor ran quietly and cycled off and on every 30- 60 seconds. I thought, 'Great, it is going to work' and shut the truck off. Two days later, I hopped in the truck, turned on the AC. The vents blew warm air. I checked the compressor, the clutch would not engage. I grabbed the gauges and found 60 psi in the system, the correct pressure for the temp that day. I retrieved my jumper and hot-wired the compressor. It started, ran quietly and smoothly and didn't change the low-side pressure at all. The system is charged, the compressor only runs if hot-wired. When compressor is running the suction line is slightly cool, the high-side line gets warmer. No noticeable cooling in truck cab. The AC indicator on the heater control flashes on/off about every 2 seconds. Is there a valve that enables or allows refrigerant to bypass and simply circulate without being compressed and forced through the evaporator? Just one time the system worked and cooled marginally okay. Next attempt brought a flashing 'AC' in heater display and no voltage to compressor clutch. Even when clutch is hot-wired, no noticeable low-side high-side pressure differential is created. Compressor is pumping as it worked almost correctly once and still has a slight 'low-side cool and high-side warm' effect on the compressor lines. Engaging and disengaging compressor clutch does immediately change engine load slightly.
Advice and knowledge welcome. Thank you for your input.

 

I'd check for leaks, That doesn't work chuck the accumulator and the orifice tube. Something is plugging your system up.