You need to have some idea what is going on before you start throwing parts at it. It sounds like you are assuming engine temp but have not confirmed anything.
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 hot to the touch. If only one is hot, the heater core may be plugged. F neither is hot, the engine temp may be low. If they are both hot, the heat in that vehicle is controlled by a blend door that regulates heated air flow. It is operated by an electric motor/actuator. The problem can be that the actuator is stripped or inoperative 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.
December, 19, 2012 AT 9:04 PM
Hopefully that will fix the problem, but I wondr, what else I should do if it is not the thermostat?