With the engine at full operating temp, locate the 2 heater hoses where they go into the firewall and feel them to see if they are both too hot to hold. If they are.
The heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by a vacuum motor/actuator. The problem can be that the actuator itself could be bad, a problem with the vacuum control head or vacuum supply or the door itself could be damaged. This is what needs to be determined by examining the actuator and see if it is responding to heat change commands or not.
Wednesday, December 15th, 2010 AT 5:57 PM