[Pat & Jan]

The first step is to verify it does not run by checking for power. You can determine if it has power going to it from the pressure switch likely easily accessed from the lower door under the driver’s side window. If the pressure is at zero, and the circuit breaker is on you should have AC power to the switch, and from the switch. No power and it could be the circuit breaker. Power on one side of the switch and not the other and it is the pressure switch, power on both sides of the switch it is the compressor.

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2025 Marathon H3 / 4th Prevost
21 Ram 1500 EcoDiesel 4x4

[Darrell]

Thanks Jon, As usual your sugestions are informative I will check out the pressure switch reight away.

Thanks again

[Larry & Diane]

Jon I just checked as you suggested and found that the pressure switch is faulty, checked power and found power to one side of the switch and I then tripped the switch manually and it started. Thanks for stearing me in the right direction

Darrell

[Larry & Diane]

If yours is like ours? The access to your aux compressor is from under the bus. In the center, just fwd of the solid axle is a vertical bulkhead. This is the rear bulkhead of the compartment behind the front bumper where 2 CruiseAir condensing units etc live. On this bulkhead is an access panel into the compartment/wooden box of the aux compressor.

These compressors have air filters on them that need servicing from time to time

6 yrs ago I removed our failing original Gast brand compressor and installed a California Air Tools 100MP and built a new wooden box for it to live in.

[Archived]

Thank you for that detailed post as I have been trying to find that hatch to get to the compressor

[Archived]

Check first at the pressure switch to make sure it closes at low pressure and sends power to the aux compressor. It is a well pump switch in the steer compartment.

Pick the low hanging fruit first.