When the vehicle is in idle the A/C comes out of the defrost and when it shifts into second gear the A/C switches to the main vents.
May 11, 2020 at 8:03 PM
Climate control
1994 GMC SONOMA
KIRK27
- MEMBER
- 1 POST
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JACOBANDNICKOLAS
- ✓ASE Certified Mechanic
- 110,194 POSTS
Hi,
What is the setting you have it set for, panel vents or defrost? I can tell you what I think is happening. The vent door actuators on this vehicle are operated by engine vacuum. At an idle, engine vacuum is much different than when driving. If there is an engine vacuum leak to the unit, that will cause this to happen.
So, first, start the vehicle and while it is running, listen closely under the dash for a hissing sound. That is usually a good indicator of a vacuum leak. See if you can locate that.
If you can't, open the hood and do the same around the engine while it is running.
Let me know what you find.
Joe
What is the setting you have it set for, panel vents or defrost? I can tell you what I think is happening. The vent door actuators on this vehicle are operated by engine vacuum. At an idle, engine vacuum is much different than when driving. If there is an engine vacuum leak to the unit, that will cause this to happen.
So, first, start the vehicle and while it is running, listen closely under the dash for a hissing sound. That is usually a good indicator of a vacuum leak. See if you can locate that.
If you can't, open the hood and do the same around the engine while it is running.
Let me know what you find.
Joe
May 11, 2020 at 8:15 PM
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