Heater will be warm until I turn on the fan, then it cools off

Tiny
ACREY
  • MEMBER
  • 2007 GMC YUKON
  • 5.3L
  • V8
  • 2WD
  • AUTOMATIC
  • 221,000 MILES
My heater will be warm until I turn on the fan, then the temperature starts to cool off. The rear heat works. I have checked the coolant level it is good. I have located the actuator beside the gas pedal, the one over the transmission hump and one on top behind the radio. How to know which one is the bad one?
Monday, October 29th, 2018 AT 9:25 AM

9 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
Good afternoon.

Before assuming the blend door motor is no good, I would suggest checking the temperature of the heater hoses under the hood where they go through the firewall.

Touch them when they are hot and tell me if they are hot. It may be a clogged heater core.

As far as the blend door, do you have dual or single controls?

Roy

https://www.2carpros.com/articles/car-heater-not-working
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Monday, October 29th, 2018 AT 12:24 PM
Tiny
ACREY
  • MEMBER
  • 5 POSTS
Both hoses are hot, and yes I have duel temp controls. One for drivers and one for passenger. It seems like the passenger side does not work as good as the drivers side does. Also, I hear a lite noise when I adjust the passenger temperature. Hear the same noise when I turn from inside to outside air.
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Monday, October 29th, 2018 AT 12:32 PM
Tiny
ASEMASTER6371
  • MECHANIC
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I attached the location of the blend door actuator for the passenger side along with the procedure.

I still think you have a clogged heater core. You should remove both hoses and flush the core with your garden hose. Flush back and forth several times until you get an even flow from both sides.

Roy
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Monday, October 29th, 2018 AT 12:37 PM
Tiny
ACREY
  • MEMBER
  • 5 POSTS
I will flush the heater core, but if it is that blend door actuator how in the world do you get it out of there? I took loose the glove compartment door and I can see it and feel it, but I do not know if I can remove it from this position.
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Monday, October 29th, 2018 AT 12:46 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Did you read the procedure I sent you?

You remove the top cover and it is right there.

Roy
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Monday, October 29th, 2018 AT 12:49 PM
Tiny
ACREY
  • MEMBER
  • 5 POSTS
Not on a 2007 Yukon. Can remove the trim around the radio and temperature controls and remove radio and temperature controls and it is not accessible from there.
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Monday, October 29th, 2018 AT 12:59 PM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,796 POSTS
This is what it shows on my Alldata.

Roy
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Monday, October 29th, 2018 AT 1:06 PM
Tiny
ACREY
  • MEMBER
  • 5 POSTS
Thanks, I will try that.
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Monday, October 29th, 2018 AT 1:18 PM
Tiny
ASEMASTER6371
  • MECHANIC
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You are welcome.

Keep us updated.

Roy
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Monday, October 29th, 2018 AT 1:21 PM

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