There is only one compressor. If you hear it run (you can't miss the loud piston pump), then it's hopefully pressurizing the air tank. The pressure switch is approximately 80 psi ON and 100 psi OFF.
Many/most of these ITVs have multiple leaks. You can pop a pressure gauge onto a QD fitting to test pressure on the labeled AIR disconnect (clean it first). Also, be sure to service your compressor and intake air filter, as many are falling apart (think intake ingestion) or caked with mud and crud so they can't breathe. Instructions for maintenance are in the TM. The POC in Yermo said some do not respond immediately, and jostling will get them "un-stuck", but that also means they need basic valve servicing (not complicated).