I HAVE PROBLEM WITH MY HEATER ALL IT DO IS BLOW COLD AIR EVERYTHING IS WORKING FINE WITH THE AIR CONDITIONER BUT WHEN I TURN ON THE HEAT IT WILL NOT GET HOT WHAT'S GOING ON PLEASE HELP IF YOU CAN.

The heater core could be pugged, but there's a better chance that the control linkage isn't working properly or the control valve is bad.