I would give consideration to keeping the auxiliary compressor in a clean area as they generally don't have a great air cleaner.
Lee,
I thought about that, but except in an emergency such as a bus air compressor failure, the aux compressor does not run when bus is moving or engine running. I felt running the compressor in the "cold" stationary engine compartment would be no worse than running it on job sites operating air nailers (what it did in a previous life). I may look at modifying the air filter to use an automotive type just to be on the safe side.
I agree it would probably not be a good thing to use it while driving down the road (except in an emergency. Jack