Air Blowing Only Out the Defrost Slots
 

On my New-to-Me Tahoe, the blower only puts air out the defrost slots on the dash no matter the position of the selctor dial. Am I going to have to remove the dash or some similar major surgery? I had a similar problem on a '98 Explorer, and $.69 door pivot would require installing a whole plenum box (@ about $400, not counting removing the whole dash and much of the forward interior).

Re: Air Blowing Only Out the Defrost Slots
 

Most likely the HVAC control panel or the Mode actuator.

1. Tap on the mode door actuator, by the accelerator pedal, check for airflow change.

2. If so, replace the mode actuator.

3. If no change, test for 12v on the Brown, ground on the Black wire at the mode actuator.

4. Test for a ranging voltage on the White wire at the mode actuator, Near 1v for defrost, Near 6v for floor and near 10v for A/C vent.

If your getting NO voltage on the white wire.....Either the Control head is bad or you have a "open" in the white wire.

BEFORE replacing the control head test the A/C request circuit for a short to ground.
This request circuit is a Lt Green wire, pin 10 at the HVAC control head. The wire leads to an A/C high pressure cut-out switch at the compressor.
From the switch to the Vehicle Control Module as a Dk Green/White wire, pin 25 of the White VCM connector.

If this wire or pressure switch has a path to ground, the HVAC control panel will fail. Look closely at the back of the compressor area for either wire touching ground.

Re: Air Blowing Only Out the Defrost Slots
 

This thread is in the wrong forum, Your 99 Tahoe is a 88-98 body style, All the above info is correct for your truck, Didnt want anybody trying these test on a 99-06 body style.

Re: Air Blowing Only Out the Defrost Slots
 

Thanks for the info!

I realize that the overlap is awkward, but, in checking past threads, I see that at least one on a '99 got moved TO this forum from the other one, so I went with that. perhaps my choice was poor.