Air Conditioning Only Come out Defrost Vents GMC Yukon



When I replaced my battery in my GMC Yukon, the Air Conditioning will not switch to come out any vents except the defrost vents. Any ideas?


I’m not familar with the Yukon but it sounds like there is a vacumm leak to your vent control unit if it is controled by vacumm. I would first look around the area where you replace your battery and see if there is a vacumm line lose, broken or removed. If you can get a vacumm diagram for your year of Yukon it may show you where this line comes off the engine then goes into the firewall and to the vent control unit. There may be a vacumm diagram under the hood.

If I’m wrong on this being operated by vacumm hopefully someone else can help.

It would help to know what year you have.


I have a 2002 Tahoe (Yukon sister) and also a Haynes repair manual.

According to this book it says there are only electrical connections to the control knobs (some MAY be equipped with control cables).

I’ve never had a problem with the Heating/A/C system so I can’t tell you exactly what is behind the panel.


To the OP, it appears you have a duct blend door stuck or disconnected.

An inspection of the heating/ a/c ductwork is a major PITA. A lot of the dash needs removal to gain access.

You can see what is connecting your controls to the system by squeezing a release clip on each side of the little control panel and pulling out.


I didn’t read back far enough, there’s more to it.

Remove the main instrument panel bezel to allow access to the heater/ac control mounting screws.

Remove the radio. (I reckon at this point you need to remember the radio code before disconnecting the neg. battery cable)
On models so equipped, remove the passenger side air bag ON/OFF switch from the instrument panel.

Release the control assembly retaining tabs and pull the unit from the dash.


Thanks Roadrunner for the correct Info. That info should help them.