What have you tried so far? Is the temperature gauge reading normally when the engine is warmed up? Is the coolant reservoir full? Do you have dual zone?
If the temperature gauge reads low, check the coolant level or suspect a stuck open thermostat. If the gauge reads normal, feel the two heater hoses after the engine is warmed up. They should be too hot to hold onto for very long. If they're cool, suspect a plugged heater core. Back flushing it with a garden hose will usually clear the blockage.
If both heater hoses are hot, there's a problem with the temperature door in the heater box, or with the actuator. If you have a dual zone heater, there are two separate actuators. The chances of both of them going bad at the same time is rather unlikely.
Some of the actuators can be accessed by removing the glove box door and reaching through to the heater box. Try tapping on them. If one starts to work, it likely has worn brushes in the motor and should be replaced.
As with everything else that has been over-engineered and unnecessarily complicated, the actuators are run with a computer instead of old fashioned, reliable levers and cables. Chrysler doesn't have near as much trouble with their computer modules as GM, but don't overlook the possibility.
Tuesday, December 8th, 2009 AT 2:33 AM