Air conditioner will not work?

Hello, I am a reasonably competent amateur mechanic although not well versed in A/C.

Earlier this spring my A/C worked fine. Then one day a couple weeks ago there was nothing. I located the clutch relay, pulled it, and shorted the power leads. The system worked and cooled. I have tested the relay for continuity when energized, also good. I have swapped that relay with an identical relay from a different circuit, no change. I have checked the clutch/compressor fuse is good.
I have tried a new pressure (trinary?) Switch, no help.

At that point I had a professional basic a/c service (evacuate, check for leaks, refill with precise amt of Freon/dye). The system checked out (slightly high on Freon, not enough to cause a problem), but they also were unable to get the compressor to run. I am currently unable to part with the vehicle for a full diagnosis.

After that I removed and disassembled my ICM (integrated control module, fuse/relay box under the hood) to check for signs of deteriorated wiring or burn marks, all looked good.
I removed my wheel well liner to inspect the PCM. There was some light surface rust on the outside and water stains, but no signs of obvious problems. I removed the four connectors and wiped everything down. The contacts looked clean.

I do not know what else to do.