Dash vents not blowing air

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MEMBER
1999 CHEVROLET TAHOE
5.7L
V8
2WD
AUTOMATIC
200,000 MILES

The cold air blows well through floor and defrost vents, but not dash vents. I replaced the mode actuator and nothing changed. I then unhooked the ground from the battery for 5 minutes, then after rebooting, no calibration took place. Not sure what else could be preventing the dash vents not to blow?

1 Reply

KASEKENNY

MECHANIC
18,907 POSTS

This is normally a mode door actuator so we need to find out if there is voltage on the mode door actuator from the control module. There are three wires and one is a 12 volt supply wire from the HVAC fuse and the white wire is going to be the signal wire. This is basically going to be less then 12 volts which is what commands it to a specific position. We need to check the voltage and then change the door position. The voltage should change along with it. If it is and it is not moving then you have another faulty actuator. If it is not moving then the control module is the issue.

https://www.2carpros.com/articles/low-or-no-air-flow-from-vents

https://www.2carpros.com/articles/air-vents-stay-in-the-defrost-position

Here is a guide that will help with checking this type of voltage. Just back probe the wire and monitor the voltage.

https://www.2carpros.com/articles/how-to-check-wiring

Below you will find the wiring diagram that will help with this. Please let me know what questions you have. Thanks

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