My ac/heater unit has a continuos light.. which is internal control, not sure what that means. I set the thersmostate at 72 and it will not keep there. It blows cold air. I turn the main electric switch on the unit off and on, and get 1 min of hot air and then cold. The house gets really cold, it will not keep that temp up on 72. What do I do? I've had the piece that controls the gas intake last year, so that's new.ugh, help!