Moose suspension problem

So Moose, who is now just 850 miles short of 100K may have a rear airbag problem. Suddenly the Check Air Ride comes on and I don't hear the compressor (which has been noisy for a couple of years). After sitting two days the rear is very low, front is so far OK. Rear does not rise.

So... what steps by process of elimination do I check. Compressor fuses, compressor, leaky bags, what? I figure it may have more to do with compressor or a fuse than a leaky bag because I don't hear the compressor at all.