Thank you for asking your question on JustAnswer, the most common cause of the problem you are having is a defective Temperature blend door actuator. (CLICK HERE FOR INSTRUCTIONS). Hope this helps you out.
Before replacing the Blend Door Actuator, make sure cooling system is full and there are no air pockets trapped in the system, also while the engine is running make sure both heater hoses are very hot, if one is cooler than the other suspect a plugged or restricted heater core.
If the hoses are only getting warm, (must be very hot) suspect a defective thermostat, as long as there is no air in the cooling system.
Make sure that there are no leaks also, any leak will lead to poor heating performance as well.
A/C Electric Blend Door Actuator
The A/C electric blend door actuator is located on the plenum assembly.
- Its function is to move the air temperature blend door on command from the control assembly.
- The A/C electric blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the air temperature blend door.
- A 5 volt signal is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EATC module and is compared to the desired wiper voltage determined by the EATC module. The control module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the desired wiper voltage.
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