HVAC stuck on dash vents

Tiny
KMONTKAHAUS
  • MEMBER
  • 2001 GMC YUKON
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 200,000 MILES
It will not switch to defrost vent, floor vents.
Where is the Expansion Valve and lines located under hood so I can check for leaks?
or is there somthing else I should be looking for?
Tuesday, September 24th, 2019 AT 3:27 PM

2 Replies

Tiny
SCGRANTURISMO
  • MECHANIC
  • 4,897 POSTS
Hello,

This sounds like this could be a problem with your mode door actuator. Your vehicle's Heating, Ventilation, and Air Conditioning (HVAC) system uses little plastic motors to control the doors that route the air into the proper vents when you direct it to go there. When these motors fail, they will be stuck in whatever position they break in, no matter what mode you choose. Here is a link down below explaining it in more detail for you:

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

Please go through this guide and get back to us with what you are able to find out.

Thanks,
Alex
2CarPros
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Tuesday, September 24th, 2019 AT 5:13 PM
Tiny
STEVE W.
  • MECHANIC
  • 13,445 POSTS
Welcome to 2CarPros. The expansion valve won't cause this issue. This is usually caused by a failed mode actuator under the dash on the drivers side. It selects the floor dash and defrost modes. To replace it you need to remove the duct extension from the HVAC box. Then you reach up and remove the screws that hold the actuator to the HVAC box. It will usually come off with the cam attached. Installing the replacement only adds the fact that you need to line the cam up with the slot and the AC cam as in the second image.
Then you need to re-calibrate. To do that you remove the HVAC fuse for 2 minutes, Reinstall the fuse and turn the key on and let the system calibrate. That should take less than a minute.
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Tuesday, September 24th, 2019 AT 5:18 PM

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