The heater core can be plugged and not leak any coolant into the car. Now, with the engine running, hot, and the heater on high, do both heater core hoses get hot? If not, chances are the heater core is plugged. Remove both the inlet and out let from the heatercore at the fire wall. Using a garden hose, see if you can get water to flow through it. Do it in both directions so you actually backflush the core. If the water flows freely, the core isn't plugged.
If that is the case, check the blend door. It is the door that determines if you get heat or AC to the cab.
Let me know what you find.
Friday, January 22nd, 2010 AT 11:28 AM