[Towncar]

Sounds like its leaking, maybe everywhere.. maybe just one place.

Solenoids can be tricky. I've seen arguments running here where the mechanic finally re-fitted the air lines properly (after many attempts) and the system did eventually work great.

One note about that compressor running.. well two notes..
Make sure it's actually putting out air.. that's the easiest thing to start with.
When it shuts down, it's overheating.. bad idea, you should be able to tell if it's working before it overheats. If it's not, take power away to protect it from burning up.