Forgot to mention, with my issue if I lift up on the right rear side a little, then the compressor shuts off, try that with your car, and if it shuts off like mine, then inspect the linkage/part#3 and see if it is still connected, if so then as Mike mentioned, the leveling senor/part#1 is most likely going bad.
I'd still inspect all lines, and strut air bags for leakage, also check the soft EVAP ones near the compressor, closest to part#20 in the compressor pic, the hoses come to a T, all of mine were dry-rotted, and one became disconnected...
I think there may also be a check valve in the system that can fail and cause the compressor to run all the time, but I do not know much about that.
2006 Pontiac Grand Prix GT with SC
1996 Buick Park Ave NA