Recently purchased used 2013 Jayco class c. Had to have some work done on the generator, it is up and running, but when I have it on I can't get the a/c to work. Everything else seems ok, but the a/c will not come on. Do I have to do something when trying to run it off generator? Works fine on shore power. Also, what is the inverter all about? should I have it on and operating all the time when using the rv, or should I only turn it on when I need it to run something off battery?