Question about 2004 GMC Envoy

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2003 gmc envoy air only blows out of floor and defrost. I hear no air leak and cannot find vacuum lines from engine to firewall. Please help. Air does blow to the rear console.

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The blend door(s) actuator is more than likely the problem, this is a common issue with this vehicle. The repair is complex, it involves gaining access to the HVAC housing in the dash. Visit and search on HVAC.

Posted on Sep 09, 2010


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Posted on Jan 02, 2017


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1 Answer

Air will not switch to floor on my 2004 envoy

it is a leak in your vacuum tree that controls the blend door. You can buy spare vacuum line at a parts store pretty cheap. $1 per foot or similar. the trick is finding the bad vacuum line. look for small plastic line coming out of the firewall and replace if cracked

Mar 18, 2014 | Cars & Trucks

1 Answer


Check your vacuum lines, check valve and vacuum canister for leaks. these doors are operated by vacuum and defrost is the default position with no vacuum. get a vacuum gauge and pull vacuum on different parts of the system like pull vacuum on the line going through the firewall, make sure it holds vacuum if it doesn't you have a vacuum leak under the dash. Next, check the line going to the vacuum canister it takes a little longer to pull vacuum on since it is a larger canister and the system uses the vacuum stored in there when the engine is not pulling enough vacuum like while under acceleration. also check the one way check valve on the line going through the firewall they occasionally go bad and would cause this. Check all other vacuum lines for deterioration and cracks and replace all or as necessary the stuff is pretty cheap at the auto parts store so you might as well do it all while you are already there. Harbor freight has a vacuum gauge pretty cheap and advance auto and auto zone have loner tool programs for free and might have one for you.

Jun 28, 2013 | 2004 Buick Rainier

2 Answers

The defrost and the floor vent does not work in my 2005 Dodge Neon... It sounds like the air is blowing in the dashboard, but does not come out of the vents

If there is no vacuum to the mode door control motor theheater/A/C system will default to "Defrost" If there is no air coming out the vents or floor - check to see if you have air blowing out the defrost vents. If there is air coming out the defrost, then the most likely cause of your problem is a broken or disconnected vacuum line that feeds the mode control switch. On your vehicle, the vacuum supply line connects to the brake booster hose under the hood. there is a check-valve on the line between the firewall and the brake booster that can fail and leak vacuum. if there is no problem with the vacuum supply line under the hood, then the most likely cause is a bad mode control switch. (switch leaking vacuum)

If there is no air coming out the defrost vents, but you can hear the blower motor running, there is most likely a resriction of airflow etween the blower motor and the air outlet plenum. I have seen A/C evaporators completely cloggedup that will not pass any air. I have also seen paers and napkins that have gotten sucked out of the glovebox area and into the "Recirc" air inlet. Another thing I have seen several times is nests made by mice or other small rodents in the blower motor housing.

Dec 05, 2010 | Dodge Neon Cars & Trucks

1 Answer

Changed battery and now a/c vents won't work, air blows out defroster and floor only.

i believe the controls are vacuum operated. when changing the battery, you most likely, however inadvertently, broke or disconnected a vacuum line. when vacuum is removed, the system defaults to the defrost postion to make sure the windshield can be defogged.

Jun 07, 2010 | 2002 GMC Envoy

2 Answers

Air vents are stuck in the floor and defroster mode in my 96 Blazer. Air will blow cold and hot, just can't change where it blows. Please advise

The HVAC door actuators are powered by vacuum, and the default position is the defrost/floor. Check for a disconnected or broken vacuum line somewhere near the passenger rear of the intake manifold. You should be able to find a line coming out of the firewall in the same area and follow it to the intake. Good luck

Nov 05, 2009 | 1996 Chevrolet Blazer

1 Answer

Air stops blowing through the vents when accelerating

u have a loss of vacuum to the ac mode control switch, this switch applies vacuum to diff vacuum motors to move air to diff outlets, dash, floor, defrost etc. either the vacuum line or vacuum resivior at the engine is leaking or the mode control is leaking vacuum.

Aug 14, 2009 | 2003 Lincoln Navigator

1 Answer

Air or heat wont blow middle vents hear clicking in dash

I have NO vents blowing on the dash , shifted from floor to defrost no trouble??? Help...AC or Heat

Jul 10, 2009 | 2003 GMC Envoy

1 Answer

A/C airflow ( 1996 Ford Taurus)

It sounds like you might have a vacuum leak. The air doors that control where the air flow goes are vacuum operated, and if a line gets broken or dry cracks, the system will go to its "default" setting, which is usually either the defroster or the floor. Start at the engine and check all of your vacuum lines, both rubber and the hard plastic ones. There will be at least one vacuum line, usually a hrd plastic one, that goes through the firewall, near where the heater box is. Check them all. Remember that there are also vacuum lines that go inside the car, behind the dash to the control head. Good luck.

Jul 01, 2009 | 1996 Ford Taurus

1 Answer

Air goes straight to defrost

You have a vacuum leak! Defrost is the default position. You need to find vent vacuum lines on passenger side near firewall under hood or under dash.

Apr 12, 2009 | 2003 GMC Sierra 1500

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