Are you sure it is the compressor. They are very reliable but do fail occasionally. Have you ruled out the governor, air dryer and safety valves etc?
The compressor is attached to the engine power take off on the right side as you face the engine from the rear of the coach. It is bolted in and has a air hose connected that goes to the air dryer. The governor is a small cylindrical unit with a couple of small air lines. Once correct pressure is reached the governor "unloads" the compressor and it free runs but does not pump air. At the same time the air dryer is supposed to purge any moisture from the dryer.
If the governor is stuck "unloaded" pressure will not build. The air dryer can fail as well and prevent pressure building. A leak in the system can also prevent pressure from building obviously.
2005 Safari Panther Diamond IV Cat C13
2013 Avalanche Toad