Does your coach have a selector switch that determines which AC can be used when on shore power? That's fairly common in 30 amp coaches. On my Coachmen for instance, the switch selects the front or rear AC on shore power, and allows both AC's to run if it's placed in the "Rear" position when our 7KW generator is running. Some coaches want the switch in the "Front" position though, to run both on the generator. Your symptoms do sound like the switch might be in the wrong position for each power mode. What make/model/year coach do you have?