We see a lot of customers with an air leak at the unloader valve on the pressure switch. The first reaction is to replace the part that is leaking, the pressure switch. BUT the pressure switch air line has no supply of air other than the tank air after it unloads.
The pressure switch is meant to release air from the lines and cylinder head above the check valve so the motor doesn’t have to start up against pressure. So if it continues to leak air after the compressor stops and has unloaded the source of air, the probably cause is tank air through a leaking check valve.
The check valve could be worn out or it might have gotten something – a screw from a valve that came loose, a piece of head gasket, etc. – stuck in it, holding it open.
This check valve leak can also cause hard starting, motor humming and tripping breakers. Let’s fix the cause and “Keep the pressure on.”