Hi,
You need to shut off the circuit breaker to that A/C unit right away. The compressor relay is stuck 'on' and it will not stop, even though no power is applied to the relay by the thermostat.
If you do want to run the A/C, turn on the thermostat and make sure that the fan is in the 'on' position, and on high speed is preferred. Then turn on the circuit breaker, run it as long as you desire the room to keep cooling, then shut it off at the circuit breaker. DO not shut it off at the thermostat, because IF the compressor keeps running (and it will until you get a new relay) and the fan stops, you can destroy the compressor. That is why it overheated and started humming.
Shut off that circuit breaker now - if you have not done so already. If you do not know how to shut off the circuit breaker, unplug the RV or stop the generator, or you can damage the $650 air conditioner beyond repair in about 5 minutes !
Good luck!
Fred.
