Heater or AC not working

Tiny
C.ROUSE
  • MEMBER
  • 2004 PONTIAC GRAND PRIX
  • 3.8L
  • V6
  • 2WD
  • AUTOMATIC
  • 138,000 MILES
My heater will not work at all, I mean the controller. I can turn the heater speed knob and nothing happens, I can turn the hot to cold selector knob and nothing happens the blend door flapper that it controls does not make a sound and also the third knob the vent selection control knob will not do anything. It appears to have power going to it as the lights on all the knobs work. I have put a new ignition switch in it [bottom electrical and lock cylinder]. I took the blower motor out and straight wired it and it works fine. I tested voltage at the blower motor and it is getting twelve volts on the hot side, I also put a new Blower motor Resister in it and still nothing happens. It has a TSB that says to put a capacitor in line at the blower motor control module I tried that to. Also, I have checked all the fuses. The battery main under the hood and the HVAC in the dash they look fine. Any Help would be greatly appreciated. Thanks
Monday, June 18th, 2018 AT 1:41 PM

10 Replies

Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
Good afternoon.

I attached a wire diagram for you to view. There are three fuses that control the heater controls. Verify power to both sides of the fuses listed in the diagram.

Lets start there before advancing forward.

Roy
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Monday, June 18th, 2018 AT 4:26 PM
Tiny
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I Checked the three fuses and they all reply good. Thanks
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Tuesday, June 19th, 2018 AT 9:01 AM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, did you verify power at the fuse on both sides?

Now verify the powers to the control head at the color wires listed. They should have voltage with the key on.

If you have voltage, then it looks like the control head has failed.

If it does not then you have a wiring issue between the fuse block and the control head.

Roy
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Tuesday, June 19th, 2018 AT 9:13 AM
Tiny
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Thanks, I will try that first thing in the morning. When you say control head do you mean the HVAC control module that you use to turn the heat and AC on?
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Tuesday, June 19th, 2018 AT 2:57 PM
Tiny
ASEMASTER6371
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That is correct.

Roy
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Tuesday, June 19th, 2018 AT 3:29 PM
Tiny
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  • MEMBER
  • 9 POSTS
Thanks Roy.
I verified power on both sides of the fuse. I verified power at the plug in to the HVAC controller, as the LED bulbs in the controller do light up, however I went ahead and followed your advice and ordered a new HVAC controller because I did have power at it and assume there is something wrong inside of it. Thanks again.
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Wednesday, June 20th, 2018 AT 8:05 AM
Tiny
ASEMASTER6371
  • MECHANIC
  • 52,797 POSTS
That is correct.

Keep us updated with the results.

Roy
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Wednesday, June 20th, 2018 AT 9:24 AM
Tiny
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Okay, thanks.
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Wednesday, June 20th, 2018 AT 10:12 AM
Tiny
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Hey Roy. Just want to say thanks for all the advice. I got my new HVAC Controller and it fixed my problem. Again thanks for all your help.
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Saturday, June 30th, 2018 AT 5:35 AM
Tiny
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You are welcome. Good job.

Glad we could help.

Roy
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Saturday, June 30th, 2018 AT 5:40 AM

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