Our '06 Monterey has always had a microleak somewhere in the left rear bag system, and the compressor commonly takes over when we are camped and tank pressure is diminished, as Gerald points out.
Another option, if you don't have a handy-dandy portable power/jump start/compressor unit to tap 12 v. from for example, or some other convenient 12v. source, is to jump across the pump's hot and ground studs with an ohm meter. Disconnecting the hot lead would be a good idea first so you can't harm the meter if the leveler panel sends juice to the pump during your test. There should be some resistance (ohms) there if the pump motor is okay. Most commonly available voltmeters have the ability to measure resistance, or continuity. Continuity means wiring is intact from point A to point B in a circuit, such as within your pump motor, and electric current can flow through it from battery to chassis ground unimpeded by a short, open switch, loose connection, or broken wire. Most meters have a simple test option for continuity with an audible continuous sound if a tested circuit is intact and okay. The voltmeter's onboard battery sends a low-voltage shot through one lead; if it goes through the tested circuit and makes it back through the meter's other lead, then you hear the sound and all is well. Theoretically.
If your pump's motor circuit tests okay, then the problem is likely upstream at a fuse or connection or perhaps a relay between the pump and the air system control unit, or perhaps a bad ground connection from pump to chassis. Check your wiring diagram book to follow leads.
