AC Unit runs when thermostat is set for heat?

When plugged into 110 volt and I set the thermostat to heat the AC unit turns on? It appears the heater is running as the air is warm but why does the AC run as well? If the temperature is not cold enough for the heat to kick in the AC unit will run. I need to turn the heat on and off manually to avoid the AC unit continually running

I'm no expert but this sounds like a problem with the thermostat. I've heard of similar problems from folks having the newer style digital t'stats. I wish I could be more help but this might be best handled by a dealer.