The PCM is the powertrain control module (or the engine computer). GM calls it the PCM, others call it the ECM.
The compressor turns at engine speed whenever the clutch cycles on and stops turning when it cycles off. The clutch is commanded by the toyota a/c amplifier.
The PCM controls the idle speed and therefore if you are standing at a stop light and the a/c clutch is activated, the increased drag from the compressor will be sensed by the PCM and it will automatically compensate and maintain idle speed. GM does use some compressor that are designed to be variable output - they don't ever cycle on and off but rather control the output of the freon pressure internally. The trucks (fortunately) don't use these compressors.
Yes - there are some cars (mainly hybrids) that use an electric motor to turn the a/c compressor instead of the gas engine. I know it sounds like a big challenge but doing custom hoses to adapt over to the gm compressor really isn't that big of a deal.
1994 FZJ80. Elocked, MAF 3/2 Lift, BFG 315 KM2s, stock 4.10s, ARB bullbar and a Warn 8074 winch.
powered by an all-aluminum 335hp L33 Vortec V8
2004 Kona Stinky dee-lux.