Check this for me. With the engine hot and the heater on, feel both heater core hoses. Both should be hot. If one is hot and the other isn't, chances are the heater core is plugged. If both are hot, chances are the blend air door is stuck only allowing cold air to enter the vehicle.
Let me know what you find. NOTE: Since it started all at once, if sounds like the door.
Saturday, October 1st, 2011 AT 4:34 PM