Here it is! First off the AC was down a pound of refrigerant so they topped that up to the 1.5lb spec. Compressor still wouldn't engage. They traced the problem to a blown 15A fuse, number 37 in the engine bay fuse panel. AC blows cold now. Curious is that they said the fuse was an "engine management" circuit so arriving home I pulled the manual out and found that this fuse protects:

Engine sensor to valves, A/C relay, PTC element oil trap, Charcoal filter (purge valve?) AND the Air Mass Sensor!

I still had the CEL and the power was still soft so I scanned and cleared all the codes which killed the CEL, the P0102, the various misfire codes, etc. Took the car for a drive and all the engine power is back and the AC blows cold. It was a fuse. I had checked the 10A compressor fuse which was good but overlooked the other.

So maybe I was right in a way. Not from a programming but a hardware standpoint. If the fuse for the other engines systems blows, the AC is prevented from running and futher loading the compromised engine.

Fuses blow for a reason though so I'm half expecting this to recur, hoping that it was a fluke.

Learning a new used car is as always, a treat.

Erwin