I have a 99' Fleetwood Wilderness with a single rooftop a/c unit. I just purchased this camper 2 weeks ago (as-is). It's in great shape and we are very happy with it. To my question and troubleshoot...
When this happens, take the inside grate off and look. I suspect your iceing up. Lack of air flow across the coils can cause this. Are you running hi or low fan?