If you hear a clicking sound, chances are the blend air door is stuck. It is the air flow vent that determines if you get heat or AC in the vehicle. Have it checked.
Also, some general things to check are: Make sure the colant is full. Is the engine running at a normal operating temp? Are both heater core hoses hot when the engine is hot, running and the heater is on?
Monday, January 17th, 2011 AT 6:53 PM