2006 C4500 Auxiliary Air Compressor

Sometimes the Auxiliary Air Compressor for the seats stays running when you turn off the ignition.

It does shut off when pressure is reached so pressure switch is working within the high and low range, when this happens I have to turn ignition on and off sometimes to stop.
I went out today and heard compressor running to fill tank while truck was sitting not running and parked in driveway.

Can the air compressor relay get stuck and keep power going to compressor with the key off.

Sounds like a bad relay. Not sure where that relay would be located...

Yes, a bad relay can power the air compressor without input from the pressure switch. The relay should be located right by the air compressor.