Air Conditioner problems of the 2002 Subaru Outback

The air conditioner begins to blow hot moist air after several minutes of working properly. Multiple mechanics including a specialty shop can't diagnose, and the only option is to replace the entire a/c compressor because the clutch isn't sold separately. I've read many accounts of the same "intermittent" a/c that only works once the engine is turned off and back on, then stops working seconds or minutes later for no apparent reason. The vehicle can be stationary or in motion and the a/c just quits.