Troubleshooting help needed-AC pressures

Unlikely the compressor outlet was lower than the suction side. You were likely reading on different gages and the HP one has less sensitivity. If you leave it sitting for a day, the two pressures should equalize, especially if it has just an open orifice tube, but even with an expansion valve it could leak around the other way past the flapper valves in the compressor, plus those flappers are one way check valves which should flow thru if suction side was higher (thinking out loud, never tested). So, after a day you expect the pressures should be the same which will tell you how the 2 gages agree. On a 70 F day, I see ~70 psig on both sides when a correct charge of refrigerant. With compressor running ~20 to 40 psig low-side and ~180 to 250 F high-side, depending on ambient temperature. I use Duracool in all my cars, but R-134A should give similar pressures.

With compressor running, if the outlet pressure doesn't increase and temperatures around the components don't change, the compressor isn't doing anything useful (i.e. compressing). Don't assume a new or rebuilt compressor is fine. I installed one in our 2002 Chrysler 3.8L from a big rebuilder in TN and it sounded funny and never worked right from the get-go but kind of worked. Next summer when it got worse, I took it apart and found they had put both thin flapper plates on one side (like to stick together). So how did it work at all? The backer plate was serving as a poor-man's flapper plate on one side as seen by witness marks from the port on it. Worked perfect with no sounds after I reassembled correctly. I used the center section from my old compressor which I had saved since much less slop between pistons and wobble-plate. That was a Denso compressor (similar to Sanden, 7-cylinders I recall). My OE compressor was fine but the clutch slipped and melted and a rebuilt one w/ clutch cost little more than clutch alone, so I went that way, but no good-deed go unpunished.