A/C Compressor assembly - dumb question

[LarryJ]

Dumb question, but I have to ask because I don't know...
When the A/C is switched on shouldn't the Compressor's external unit be rotating also, and not just the belt ring?
In other words, in the photo below, with the Compressor on the right, shouldn't the assembly represented by those 3 screws be rotating also?
(Because they're now not - only the belt pulley ring?)

[Sapientoni]

Yes, if the switch is engaged, the entire a/c clutch should be turning. There are a few things that would prevent this. There is a low pressure switch, a high pressure switch, wires pulled loose, the environmental vehicle controller (if the car has one). To check the clutch itself you can jumper the clutch and when circuit is closed it should engage. I had a Caddy melt the serpentine belt because the compressor failed and locked up.

Good luck and be cool.