Bran,

Can you send a picture? The aux system on mine is strictly a well pump switch and it opens or closes the circuit to the compressor. I am unaware of any pressure relief valve on the aux system.

When a bus is exposed to colder temps all sorts of changes take place. Suspension valves that never leaked all of a sudden aren't working so good and the bus leans. Coolant hose clamps aren't tight enough anymore and coolant may drip a little. It is the bus's way of telling you that you need to point the bus south and start driving.