[77newell]

If you have no power at the receptical the 120vac compressor is normally plugged into, that raises the question of whether you have 120vac anywhere. Does other 120vac powered stuff anywhere in the coach work? If yes, then I would start at the cb box and work downstream towards the compressor receptical. If no, then I would start checking for power at the post and work towards the cb box.

If the 12vdc compressor runs when it's air outlet is disconnected but not otherwise then that outlet line somewhere downstream is blocked, possibly by ice if the weather is cold enough.

I started each paragraph above with "if" because I'm guessing at what your description meant to describe. When troubleshooting, the devil (actually the solution) is revealed in the details. A precise and detailed description is necessary to maximize the probability that the responses provided via this site are helpful in solving the problem you actually have and not one a reader infers from a.terse desciption. I can't believe I actually found an appropriate way to use the word "terse". Woohoo.