2005 Trailblazer Blower motor is completely inoperative

85

Asked by Sep 15, 2015 at 03:32 PM about the 2005 Chevrolet TrailBlazer LS 4WD

Question type: Maintenance & Repair

I have a 2005 Chevy Trailblazer and the heating / AC blower motor does
not spin at all on any setting. I have checked the voltage at the connector
and it baffles me. In position 0 it's zero volts. Makes sense. Position 1, 2,
and 3 it's 13.4 VDC. This makes no sense to me. This is a DC motor, no
logic, just a DC motor. I thought the way the speed was adjusted was by  
lowering toe voltage to slow the speed. In position 4 (highest speed setting)
the voltage varies rapidly around 20 to 400 millivolts. I took the blower
motor out of the truck and on the bench applied 12V from a battery
charger, it spins strong and healthy. I replaced the resistor even though the
old one seemed to be fine, but that also (not surprisingly) did not solve the
issue. When it died, it died all at once. Just didn't work at all one day.

What confuses me most, why does the fan not spin if there is 13.4VDC at
the blower motor connector? I used the connector from the old resistor as
a test fixture and it worked fine so not a corrosion problem on the motor
power pins. I'm at a loss as to why applying power on the bench works, but
voltage measured in the car as ok does not spin the motor.

There is a technical bulletin on this that says there is a bad ground under
the carpet in some models, but I measured the voltage across the
connector. If the ground were bad wouldn't that show up as low voltage?
Unless it's ok until I try to pull current through it.. Any ideas?

1 Answer

85

I found the problem. It is in fact a bad ground. The service bulletin about this is in fact the problem here, it's corrosion around a ground under the carpet. Now to figure out how to get under the carpet without removing all of the center console.. BTW, to test if this is the problem you can: 1) Strip both ends of a piece of wire and push one end into the blower fan connector on the ground (black wire) side. (Do this with the connector still attached to the blower. You're pushing it in from the outside end of the connector shell.) Insure you are contacting ONLY the black conductor in the connector shell. If you are touching the red wire, it will short to ground and you will pop fuses and potentially damage the resistor pack or other components. 2) Turn the motor to the off (zero) position 3) Start the Trailblazer 4) Touch the other end of that wire you prepared to a piece of exposed frame in the now exposed area behind the glove box 5) Turn the blower motor switch through all of it's positions. If it spins, then you have a bad ground under the carpet and you need to go clean up the corrosion that's preventing good contact. All this procedure does is create an alternate ground path to see if that's the problem. If this does not cure it, then I would bet that either the resistor, or the blower itself are toast. Follow the directions on YouTube or any of the DIY sites and remove the resistor pack. If it looks or smells burnt, that is the likely candidate. Just be sure you made god contact inside the connector shell with that wire or the test didn't really help you find the problem. Before you buy a new blower, remove the old one from the Trailblazer, and apply 12V to it on your workbench. If it spins the problem is in the car and you don't have to replace the blower motor.. I hope this added info was helpful.

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