Question about 1990 GMC Sierra

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2004 GMC Sierrsonly works on heat no defrosters or vents

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  • 278 Answers

Blend door malfunction. check for a broken door, or bad door actuator.

Posted on Oct 26, 2012

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Posted on Jan 02, 2017

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SOURCE: 1999 gmc safari van upper vent

Check under the hood for deteriorated small vacuum hose coming off the intake over to the heater box area.
Repair the vacuum hose.

Posted on Oct 31, 2008

csmock132
  • 4669 Answers

SOURCE: 2004 GMC Envoy; Very little air flow from FRONT PANEL

Try replacing the cabin air filter.

Posted on Mar 12, 2009

alicantecoli
  • 22219 Answers

SOURCE: a/c and heater only blow air out of defrost

either a vacumn pipe is broken or the ends split so its not passing a vacumn to open the flaps,where they are and how to get to them i cant help because i have never worked on one as they are not here in spain.check the engine end first though .Look for some small rubber pipes running from the inlet manifold

Posted on May 30, 2009

  • 460 Answers

SOURCE: I replaced heater core in 1999 gmc sierra 1500 5.3

no,, the system works from a vacuum and has to be worked on in a service garage. sorry about the bad news...

Posted on Nov 12, 2009

  • 326 Answers

SOURCE: 2004 gmc dual ac, driver side vents shift from ac

bad blend door actuator maybe there is way to press the buttons on controller to make doors recenter they call it

Posted on Mar 22, 2010

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Related Questions:

1 Answer

Heater only works on heat won't switch over to defroster or vents


Sounds like the blend door. The actuator motor is located on top of the box (behind the glove box) and is notorious for failing.

Oct 26, 2012 | 2004 GMC Sierra

1 Answer

On my 2004 Gmc Envoy, Heat only comes out on passenger side, still blows cold air on drivers side. Defrost, floor and vents all produce air flow. Rear heater works fine. A/C works fine. Any idea?


Sounds like the driver's side temperature actuator or blend door are defective. Part of the dash needs to be removed to access these parts.

Oct 26, 2011 | 2004 GMC Envoy

1 Answer

2004 trailblazer dash vents fail to blow heat. All other vents work normally. I could not locate a vacuum hose that I thought might operate the upper dash vents. what do you suggest? Thank you.


this vehicle has electronic acuators that move the doors and do not use vacuum. the mode door actuator is bad causing this problem. there is a defrost acuator that works the defrost position and a mode door that works floor/vent operation. the defrost moves and diverts airflow up defrost vwents this is why you can still have defrost and floor.

Mar 09, 2011 | 2004 Chevrolet TrailBlazer

1 Answer

A/c and heater only blow air out of defrost


either a vacumn pipe is broken or the ends split so its not passing a vacumn to open the flaps,where they are and how to get to them i cant help because i have never worked on one as they are not here in spain.check the engine end first though .Look for some small rubber pipes running from the inlet manifold

May 30, 2009 | 2005 GMC Sierra 1500 Hybrid

2 Answers

Dash vents not working


It may be the actuator not working properly. Should be above the accelerator pedal to the right.

Keeme

Jun 26, 2008 | 2004 GMC Envoy

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