Jim,
It could be as simple as resetting the CB for the condenser fan.
First, determine if the condenser fan is running. It is the one on the passenger side. With the bus running and AC "on" just check to see if you hear the big blower functioing. If not, find the circuit breakers. I have no clue where it will be located on your vintage coach. On my previous one it was located in the top of the first bay, driver's side.
I have not had any AC problems on this coach so I have not gone looking.
The CB, if it needs to be reset, is a hard one to reset. I have to push on it with a tool because my thumb will not do it. It does not look like it is tripped if it is tripped. It is a big red one.
If it is not tripped it could be low freon.