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Heater controls?

5

540s10

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Location
Shrewsbury,MA
I've noticed that none of the vent positions on my truck blow very strong, and whatever selection I put it on I always get some residual heat blowing from the other vents (making my cold soda turn hot). Both the hot/cold switch and fan speed switch work as they should.

Is this something commonly related to the switch itself or should I be looking at the flap that dictates the flow to the vents?
 
Could be the mode selector portion of the control board that was what mine turned out to be.

When I get a chance I'll paraphrase the diagnostic flowchart from GM manual. There is a plug you can take off on the duct box above the transmission hump and probe the pins that should diagnose either board or electric motor/mechanical issue with duct flapper. If someone knows feel free to beat me to it. Mine was really slow to change to defrost and would "leak" like you are describing.

Its fairly common for the control board to go out. Not hard to change. Was around $120 iirc from gm parts direct dot com 2 years ago I think but don't bet on my memory.
 
It could also be a stuck blower door, or a dysfunctional door motor. You can try running the door motor off of a battery, if it works that would limit it to a wiring problem or the controller.
 
The mode door actuator motor is the one next to the throttle pedal. It is common for the motor to burn out or the gears to strip out. Another possibility is that something got dropped down the defroster and is jamming the flapper valve inside the housing. I had the linkage fall off on my 95LD. I had to take the dash out to fix it. The actuator motor is easy to replace. With the engine off ,key on ,listen for motor running when you switch modes. If it runs but the mode doesn't switch ,it stripped its plastic gears.
 
Crankme69 said:
How hard is it to change the door actuator motor / gears, do I have to pull the dash?
Click to expand...
The motor and gears are one sealed unit. 2- 7mm hex screws hold it on. No the dash doesn't have to be removed to just replace just the actuator motor.
 
the vent motor is very easy to replace and is interchangeable with the hot cold motor. You could take both off and swap them and then if your hot cold doesn't work you know the motor or threads are stripped. here is a pic of the motor. the part # is 604107 and the cost is 33.79 at http://www.rockauto.com/catalog/raframecatalog.php
getimage.php
 
540s10 Hope ya didn't mind me jumping in on yr post? At least it keeps my coffee warm on the way to work in the morn LOL!!!

BK Thanks for the answer on the dash not needing to be pulled.

Ed Nice PIC Thnx I need all the visual aids I can get, I'm not getting any sharper with age!
 
Sorry I did not see the info I was looking for in the helm manual. They are hard to find stuff in sometimes. I don't like the index organization.

I'll try again later but no promises. IIRC it was fairly easy to probe the points and this did a good job of diagnosing the control board vs motor. But can't remember procedure. I think it was 0, to 5v depending on which mode selected for one of the connectors near throttle pedal on the motor plug mentioned in above post.

It could me a mechanical issue but if it works good sometimes could be voltage issue because you are suppose to be able to blend the vents.
 
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