Chevrolet Repair: air flow severly diminished when defrost in engaged, automatic temperature control, quality hand tools

Question
QUESTION: Hello...I have a 1997 tahoe 2dr 4 wheel drive 5.7 liter. When I turn on the defrost and crank up the fan, very little air is coming out of the defrost vents. the air is blowing out in the floor vents and even the upper vents. When i have the fan turned down i hear some clicking noises under the dash like relays or something. the fan seems to be fine...any suggestions..thanks for your help

ANSWER: Hey Troy,

 Sounds like the mode selector door servo is not working properly and not closing the door all they way.  The controllers fail as well on the Automatic Temperature control units.  If you lower the glovebox you should be able to see the edge of the mode selector rods and servo's moving when selections are made.  The servo's and motors can be very time consuming and tricky to replace without experience or quality hand tools.


Wayne Howie



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QUESTION: would replacing the control module help? Or do I need to have it diagnosed properly?? thanks again

Answer
Hey Troy,

  With the amount of variable that makes air flow and direction on those vehicles combined with the common amount of component failures I would suggest swinging by your local repair facility.  They can probably advise on what to do and estimate it for you pretty quickly.  Some vehicles only have one common problem or two but those GM's can be anything or something new.

Wayne