If your heat doesn't work in the fronts, check the air door actuator and the water valve.
Air door actuator is right by the left foot of the Passenger's foot. Take out the middle console like leather shifter cover, arm rest, the whole middle console. Then you'll see it. Turn your heat from cold to hot to see if it moves. It will open/blend/mix the air door in the heater unit and open or close to water valve in the engine compartment.
Water valve is not likely but check as well. It could be stuck or cable could come off.
If there's no heat in the REAR. Then it could be the water valve in the back/rear. It's also an actuator, it's located in the rear AC/Heater unit. Take it out but be CAREFUL not to break the two aluminum pipes/tubing that antifreeze go in and out of. This will be another job you don't want to do.
Check the motor, run 12volt DC to it. Not sure which pins right now. Positive goes to one pin, Negative goes to another on. There's like 6 pins or so. Something like that.
This will fix it.
Hope this help people.
Monday, December 16th, 2013 AT 1:39 PM