1997 HVAC strange operation.

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Madscientist

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I have a 97 crew cab that i have replaced and updated alot of stuff on. It has new hvac control unit in it, (as the temp control did not work prior to new unit.) It was stuck on defrost as the top blend door had fallen in. I tested the operation of all the functions and when the fan is off, everything works as it should. Turn fan on ,(any speed) and the blend door motor centers itself and charging from defrost to feet or both, it ever so slightly works. Anyone ran into something like this?
 

alpinecrick

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Or are you saying the blend moves when you switch the fan on?

When the fan is off on my 96 and 97, the blend doors seem to move into a neutral position. If I understand you correctly, yours seems to be doing the opposite.
 

Madscientist

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Or are you saying the blend moves when you switch the fan on?

When the fan is off on my 96 and 97, the blend doors seem to move into a neutral position. If I understand you correctly, yours seems to be doing the opposite.
You are exactly right on that. They work as they should when the fan is off . Turn the fan on and they move to a center position regardless of the settings
 

AK49BWL

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There's a wire coming from the back of the fan switch, I want to say green, that should be live only when the fan is off... It loops around and connects at pin 3 of the long gray connector on the opposite side from the fan switch - it's supposed to tell everything to shut off - A/C, recirc, center the blend door, etc. I cut mine out because it started doing stupid stuff while the blower was off - only thing is I just have to make sure my A/C is off myself now. I like being able to put the blend door where I want it so I can still get airflow from driving with the fan off now. Always thought the re-centering when the system is off was the stupidest thing... And all vehicles do it! Why??
 

Madscientist

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Thanks for your reply. I ended up testing what had power when the fan was off and what turned off when the switch was on. I ended up running a jumper wire from the purple on the switch, which was hot with the key, to the blend door switch power and everything works as it should. no idea why it quit or i guess if it ever worked at all as the upper flap had fallen i . Got it taken care of but thank you!
 

Madscientist

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Next on my agenda is to finish up my ac wiring from when i did my 5.3 swap. A person is never done ******* around lol.
 
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