Chevrolet Repair: 95 Tahoe Front Window Defroster, chev tahoe, automatic temperature control

Question
QUESTION: I have a 95 Chev Tahoe and I do not get the air diverted to the front windshield when I turn the switch to defrost.  The fan is running and you can hear the air under the dash but it does not come out (very little) of the windshield vent.  If I change the switch to the floor or front vent I get the air coming out.  I just don't get it out of the windshield defroster.  How does the damper switch?  Is it electric or vacuum? What can I check?

ANSWER: Hi Todd,

 Lets get a little more aquainted with the system.  Does it have automatic temperature control?  IE do you set a digital temperature or just turn a knob to the blue or red.

Wayne


---------- FOLLOW-UP ----------

QUESTION: You just turn the Heat/Cool knob to Red, Set the selector switch to defrost (front windshield symbol) and turn on the fan.  I do not have digital temperature settings.

Answer
Hey Todd,

 The doors are controlled by servo motors that feedback postion to the controller head.  It sounds like the mode control servo is defective.  I f you expose the motor and put your hand on it and try and change positions you should feel in hum in your hands.  Thats a really sad way to test it but if you have a DVOM and know how to use it I can guide you through the diagnostic procedure.  I have replaced mode door servos and quite a few control heads for that very problem.

wayne