Cannot get heater to switch to defrost or floor position

GENERALACE

MEMBER
2003 MITSUBISHI DIAMANTE
3.5L
6 CYL
FWD
AUTOMATIC
57,000 MILES

My heat works just fine but seems to be stuck in the front position. It will not blow on the windshield when I put on the defrost or on the floor when I put it on the floor setting. I am assuming the vent door that directs the hot air is stuck but not positive. Any insight would be greatly appreciated.
Thanks

1 Reply

STEVE W.

MECHANIC
13,445 POSTS

Okay so you can control the temperature hot/cold but cannot control floor/dash/defrost and it is stuck on dash correct? That would likely be either the linkage/actuator motor (items 3 and 4 in the picture) or the control head itself.

To get to the actuator-
The lower instrument cover has two screws and clips that hold it in place. Once you remove it the actuator and linkage is right there on the HVAC case.

You can test the actuator using battery power and a couple jumper leads. Remove the connector and apply twelve volts to terminals 1 and 3 on the actuator. It should move one way. Reverse the leads and it should move the other direction. If that part works it is probably the position sensor that is failing. It is part of the actuator.

If it does not move you can try moving it just a bit by hand and see if it starts working. It could simply be stuck, but I would not trust it to keep working if it was just stuck.

If it does not move at all you can check for voltage coming from the control head on those same two pins.

Images (Click to make bigger)