Heater stuck in on position

[breaksr]

My '91 Q with 215K has recently encountered a new problem. The heater seems to be stuck in the 85 degree mode no matter what temperature I set the climate control. Even turning the A/C on (Auto setting) I still get very hot air coming out of the vents. This problem occurs at all speeds. I've read the posts on the heater door getting stuck but it looks like that just causes there to be no heat. What should I check?

[Q45tech]

Follow diagnostic proceedure in FSM to test all controls/motors.

There are 125 pages to read, reread, and study.

No reason why the shaft cannot break/stick in the open position.

When was the HVAC air handling system removed for cleaning and lubrication? The answer is probably never.

[breaksr]

Yes Dennis the answer is "Never". I use to hear the door close when I pressed the "Off" button on the climate control. I'll check the FSM and go through the diagnostic. The car never had very good heat to begin with and now it is so hot you can burn your hand at the vent. Thanks for the help as usual you sure have been around for quite a while.

[maxnix]

Dennis has seen more owners pass through this and previous boards than are on here now.

There is an interesting post about a self repair without removing the mixer box. Wes has a nice post about how to get in there.

[breaksr]

I read through the service manual but I did not have a chance to run the diagnostic as of yet (just to familiarize myself with what to check). Last night while driving home everything operated correctly but this morning half way to work I started to get max heat again. It's interesting how the climate control starts to fail. First the vent starts to give off some warm air (ambient temp 52 with climate control set at 72) with the flow of air at both feet and face. Then as the air temperature at the vent heats up the climate control redirects all of the air at my face (all vent). I suspect the climate control is trying to cool the interior but it is fighting a losing battle since there is too much anti-freeze flowing to the inside heater core. I'll run the diagnostic and hope I get a code since this happens only after driving the car for several minutes (roughly twenty).