92 Q45 defrost stuck on?

[bigox777]

My 92 Q45 had the heater display unit go out , and then a few days later the defroster wouldn't turn off.Today I put in a new display, but even when I turn it off it keeps defrosting. Does anyone know how to fix it?Jake

[Q45tech]

Follow the diagnostic proceedure in FSM. You can manually control/check the position door [which may be stuck, motor failed, or position sensor failed].

[bigox777]

No FSM, no luck!Serves me right,lolthanks

[bigox777]

Where is the position sensor located and what does it do?Everything is working fine, except after I hit off the blower stays on.

[Q45tech]

Each of the electric motor operated air control doors has a position sensor to confirm to the HVAC computer that they [the doors] did what was commanded.

Potentiometers send back voltages to HVAC ecu.

The 94-96 were bad about breaking the plastic pin pivot hinges on the heater door.........because owners didn't cycle the system to heat in the summer /just like they do not test the AC in winter and grease dirt builds up sticking the foam seal surround.

Changing a heater door can be an interesting ALL DAY [sometime 1.5 days]job for a master tech as the entire dash must be stripped down to nothing and reassembled correctly.

[bigox777]

I just read an old post about someone that had the same problem.They said there is an amp that they replaced to fix the problem. Q45tech - do you think that could be the problem? If so, exactly what is this amp called so I can order one?Thanks for your help

[Q45tech]

Think you are referring to the fan motor speed control [amp], actually when the unit fails you only have wide open max fan speed or no fan speed -------nothing in between.

[bigox777]

That seems to be the problem, it is stuck on max.Thanks for the quick responses. I'll let you know what happens.

[Q45tech]

But you told us it wouldn't turn off and it was stuck on defrost, not that when the unit was turned on that the fan was at WOT.???????????????????????INET dianostic are difficult

[bigox777]

Sorry about the confusion. I should've explained it a little better. Good thing is that after reading that old post and checking with Q45tech, I went to the dealership and bought the blower amp.About 10 minutes to install and the Q is back !!! I've never had a problem that wasn't solved on this board. Thank you to all the members that help me everytime !!!