Problem when running heater

[Holeshotdan]

I just purchased a 16' Eclipse Iconic 44.5 ft Toyhauler. When I turn the thermostat to turn on heater it starts up and everything is working fine. After a hrs or so if I turn the heater up my overhead rooftop a/c unit also comes on. Is this normal ? When it's on it just blows cool or cold air, the same time when the central heater is on. I have also noticed a noise underneath the refrigerator that sounds like a flapper for the heater moving back and forth. It is extremely loud and scared the **** out me the first time we took it out and used it. Can someone please chime in and let me know what the problem might be ? I'm pretty sure thatvthe rooftop a.c. shouldn't be coming on when you only have the thermostat set for the heater. Need help
Thanks Dan H

[cavie]

You have a "heat pump system" The comp is running but it is not producing cold air. set the t-staT TO FURNACE.

[arhayes]

In our unit, you can select cool, auto, fan, or furn. If you select auto, the furn will come on BUT the AC can also come on if it senses the temp getting where it might be needed. We either select "Cool" for AC or "Furn" for heat and have no problem. YMMV