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Blend Door Actuator?

Tiny
DEREKJL
  • MEMBER
  • 1999 CHEVROLET TAHOE
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 129,000 MILES
I installed a new mode door actuator (the part that controls air flow direction) the other day and had a question regarding whether or not I did it correctly. I made sure that the main dial was in the OFF position and the truck was turned off before starting. I took the old one out and put the new one in. However, I did NOT re-align the white shaft within the dash to the new actuator. Was this something I was supposed to do. I've heard of this step while replacing the temperature actuator behind the glove box but not with the mode actuator. Also, was I supposed to disconnect the negative battery cable and wait 10 minutes for the unit to "reset"? The modes work fine with the exception of a slight delay when switching from defrost to the front (face) mode. When this happens I can hear the flap inside the dash switch around. Is this normal? Thanks for any help. I appreciate your videos and have learned a great deal from them.
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Tuesday, April 7th, 2015 AT 11:36 PM

24 Replies

Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,772 POSTS
If it is working other than a slight delay, leave it alone. You didn't do anything that will hurt it.

Here is a guide to help

https://www.2carpros.com/articles/replace-blend-door-motor

Please run down this guide and report back.
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Wednesday, April 8th, 2015 AT 5:07 AM
Tiny
WINK1212
  • MEMBER
  • 3 POSTS
  • 1999 CHEVROLET TAHOE
  • 5.7L
  • V8
  • 4WD
  • AUTOMATIC
  • 155,000 MILES
I only have air/heat coming out the defrost (some slightly through the floor) and I have already replaced the blend door actuator under the floor pedals. The problems still exists, so what could still be the problem?
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
You need to check mode door actuator. Try pulling fuse first for sixty seconds with key on it may reset and be okay otherwise see one in picture. Blend door actuator is for temperature like heat to air conditioner.
Image (Click to make bigger)
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
WINK1212
  • MEMBER
  • 3 POSTS
That might be what I replaced (mode door), it was under the dash above the gas pedal. I replaced it and I see if moving when I change the controls from floor to defrost, but the blower still comes mainly through the defrost. The mode door controls where the air goes right?
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,702 POSTS
It sounds like the blend door itself has broken loose from inside the heater plenum. But to be sure remove the actuator and work the pivot by hand with the heater on to see if the door makes any changes.

Please let us know happens so it will help others.

Best, Ken
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
WINK1212
  • MEMBER
  • 3 POSTS
Ken, yeah I had did that a while back also, I pulled off the actuator and manually moved the arm up and down, but it didn't change any direction of the air/heat movement. So does that mean I need to pull the dash apart to fix? Thanks
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
HMAC300
  • MECHANIC
  • 48,601 POSTS
No you probably took the wrong one apart the pic shows correct one it may be a broken door or shaft
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
GARY BURNS
  • MEMBER
  • 2 POSTS
  • 1999 CHEVROLET TAHOE
Air Conditioning problem
1999 Chevy Tahoe V8 Four Wheel Drive Automatic 150k miles

my a/c vent control does not function properly. Switching from windshield to air ducts it sticks and does not complete the transition. How does this system work? How do I get at it?
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
JACOBANDNICKOLAS
  • MECHANIC
  • 109,772 POSTS
Actually, in this case I believe you are looking for a vacuum leak. The vent doors are actuated by vacuum. If there isn't enough because of a leak, it will cause this. Check under the dash for damaged or disconnected hoses. Also, with the engine running, listen for a hissing sound.

AS far as access, you need to remove part of the dashboard, glovebox. To access the HVAC system and the vent doors.
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
KEN L
  • MASTER CERTIFIED MECHANIC
  • 47,702 POSTS
If you moved the blend door pivot by hand while the unit was on and no air direction changed then yes the blend door is broken and the heater plenum needs to come out to be taken apart to see what happened.

Please let us know happens so it will help others.

Best, Ken
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
KLEMM
  • MEMBER
  • 3 POSTS
  • 1999 CHEVROLET TAHOE
I have a 99 Tahoe that will not switch between defrost, vent, floor, ect. It will blow heat and A/C but will not allow me to switch between the various outputs.

Thanks for any help, it's appreciated.
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Sounds like you have a broken vacuum line somewhere under the hood. Usually goes through the firwall near the a/c accumulator
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
KLEMM
  • MEMBER
  • 3 POSTS
Awesome, can you point me in the general direction of where the A/C accumulator would reside?
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
2CARPRO JACK
  • MECHANIC
  • 11,533 POSTS
Passenger side of the firewal in engine compartment. It is a small black plastic vacuum line
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Monday, July 8th, 2019 AT 3:24 PM (Merged)
Tiny
BIGGWAUKEGAN
  • MEMBER
  • 4 POSTS
  • 1997 CHEVROLET TAHOE
  • V8
  • 4WD
  • AUTOMATIC
  • 1,200 MILES
1st timer here so be easy on me. 97 Tahoe with new radiatior, thermostat, motor and waterpump. Heat is blowing cold but motor is not overheating. Both hoses going into firewall are warm but not hot. Could this be my heater control valve? Heater door actuator? Help me please its like 10 degrees here in chicago and Im cold
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
If it has a heater control valve check it-and also retest the thermostat and check the air blend door-
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)
Tiny
BIGGWAUKEGAN
  • MEMBER
  • 4 POSTS
How do I check the heater valve without replacing it? Its like$11 so Ill just replace it. Gonna swap out thermostat too. Would the air blend door cause cold heat?
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)
Tiny
BIGGWAUKEGAN
  • MEMBER
  • 4 POSTS
Hers the ***
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)
Tiny
RASMATAZ
  • MECHANIC
  • 75,992 POSTS
If its stuck in the cold position-check the door actuator/vacuum
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)
Tiny
BIGGWAUKEGAN
  • MEMBER
  • 4 POSTS
If the blend door is stuck in the cold position? Please be more detailed with your responses. Sorry but I need details so I can get this fixed
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Thursday, September 24th, 2020 AT 10:31 AM (Merged)

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