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No HVAC, no power at the resistor and fan motor

Tiny
JOHN MACKEY
  • MEMBER
  • 2006 CHEVROLET TRAILBLAZER
  • 4.2L
  • 6 CYL
  • 4WD
  • AUTOMATIC
  • 145,000 MILES
Changed resistor, dash control module, ignition switch. Checked ground cluster on floor. All fuses and relays are good. Manual A/C heat.
Tuesday, June 23rd, 2020 AT 8:41 AM

9 Replies

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

I attached a wiring diagram for you to view. There is a blower fuse, 40 amp, that needs to be checked. This is not a visual check but a voltage check. Verify voltage on both sides of the fuse. That is what powers the resistor.

https://www.2carpros.com/articles/how-to-check-a-car-fuse

Check the red wire at the resistor for power with the key on.

https://www.2carpros.com/articles/how-to-check-wiring

Let us start there.

Roy
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Tuesday, June 23rd, 2020 AT 9:39 AM
Tiny
JOHN MACKEY
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Roy, I pulled that 40 amp blower fuse and when I put a volt meter across the terminals I showed no voltage! I pulled the 40 amp fuse next to it and I showed 12 volts. Nothing at the red wire on the resistor! I was going to put 12v on the fuse terminal but I was afraid I might damage something else. The schematic shows s250 on the red wire. I do not know what that is. I know s201 is the ground cluster at the console floor.
Thank you, Roy.
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Tuesday, June 23rd, 2020 AT 5:29 PM
Tiny
ASEMASTER6371
  • MECHANIC
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Okay, when you test for voltage, use a test light or voltmeter.

Black lead to a chassis ground and red to the fuse terminal.

Are either terminals show voltage?

Roy
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Tuesday, June 23rd, 2020 AT 5:34 PM
Tiny
JOHN MACKEY
  • MEMBER
  • 5 POSTS
I used a volt meter and only one terminal showed power! I went from battery ground to the rear terminal on fuse 35 and it 12 volts. When I jumped across both terminals on fuse 35 I got 0 voltage! Where is that chassis ground? I see 2 body grounds by the fuse block!
Thanks for your feedback!
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Tuesday, June 23rd, 2020 AT 6:13 PM
Tiny
ASEMASTER6371
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With the fuse out, there should only be 1 power. If you install the fuse, then both sides should be hot.

There are no grounds. All the circuits in the fuse block are power. The fuses are protection for the circuit. It is in series with the circuit.

If you jump across 35, then there should be power to the red wire at the resistor.

Roy
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Tuesday, June 23rd, 2020 AT 6:30 PM
Tiny
JOHN MACKEY
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Roy, but when I put my volt meter across both terminal on 35 I showed no voltage. Is that correct? Or should it show 12 volts? This is with the key on and the dash control on #4!
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Tuesday, June 23rd, 2020 AT 6:39 PM
Tiny
ASEMASTER6371
  • MECHANIC
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That is not the way to test it at all. You never put both leads over the 2 terminals. That is not a test. It is an open circuit. The fuse completes the circuit.

Roy
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Tuesday, June 23rd, 2020 AT 6:52 PM
Tiny
JOHN MACKEY
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Thank you Roy for that feedback! I have 12v at the resistor on terminal G but I have nothing else! No power to the fan motor. Could the new resistor be bad?
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Wednesday, June 24th, 2020 AT 4:59 PM
Tiny
ASEMASTER6371
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Okay, if you have power on the red wire or G, and no power to the blower, then yes, it is a bad resistor.

There is a relay inside the resistor that seems to be the issue.

When you tested it after getting power on the red wire, did you turn on the control to blow air?

Roy
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Wednesday, June 24th, 2020 AT 5:14 PM

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