I am not familiar with your coach air conditioning specifics, but perhaps some generic suggestions may help troubleshoot your problem. If the thermostat operation is typical, I would "assume" there are three micro relays inside; one for each roof air conditioner. When you call for cooling you should hear each micro relay operating in the thermostat when it tries to switch on the relay control of each appropriate air conditioner. If you have proven the 120VAC feed is good to the failed air conditioner you might have a bad low voltage control wiring connection in the air conditioning plenum or even at the thermostat. I am attaching a very generic schematic of a typical air conditioner on a single thermostat.....wiring colors may not apply to your situation, but the basic operation should be similar. The relay shown is probably up in the plenum area of the air conditioner....usually accessible from inside the coach by taking the roof panel and air filter out. You could check to see if the low voltage call for cooling is actually coming from the thermostat.