As far as compressors and sitting...
The pulley is mounted on a double race ball bearing. It freewheels. When the clutch is energized, the compressor rotor is engaged to the pulley. The compressor rotor is connected to the flat plate with the 3 tabs sticking off of it that are for the safety [seized compressor] cutout. That is what you want to turn to see if the compressor is stuck. You do also want to spin the pulley to check the ball bearings, but that's a lot easier to fix than the internals.
Sitting shouldn't hurt them, there is refrigeration oil in the Freon loop, and it is circulated through the system. Sitting outdoors, in high humidity, and wide temperature swings, with open lines, well that could cause problems.