Tom Faust

First, I have to admit that I am scared of anything I can't see until it is too late, and can move through a wire.

Thinking a mouse nest had burned up the heater blower motor in my 16V Scirocco, I recently replaced my heater blower motor with a used one. That was the easy part of the job.

Well, the replacement motor won't run either. I suppose the replacement motor could be bad.

Here's the deal, using a test light, I have checked it from the fuse to the motor. The circuit tester light lights everywhere from the fuse to the armature of the motor. So, power is getting there. The armature is exposed and I get a circuit test light when I touch the armature with the probe. Should this be? I am wondering about the ground.

In case my nomenclature is off, the tester I am using is not powered. So when I get a light, I am finding power.

The 5 pin connector that ties the series resistor into the system is a "one way" connector, so I am pretty sure that is right. I checked the color coding of the wires on both sides of the connector, appears correct.

The series resistor for motor speed has soldered connections, so I used the one that came with the used motor. I don't think there are erroneous connections there.

treehunter

you hit the negative pin.

Will it take off if you give it a spin by hand under power? How badly worn are the bearings and brushes?

Tom Faust

Helping it spin with power on doesn't help. Bearings? Bushings? Don't know. I spun it by hand before putting it in, didn't make any noise.

Will Ng

The reason I ask is that some HVAC systems are actually switching GND, not +12V to the motor.

If you still have the old motor, verify it's actually dead by attaching it to a 12V battery.
If it works, then, we know the problem lies in the VW's wiring.

An example of how some HVAC fan motor circuits are wired:

Fused +12V to the motor can be switched or constant.

The "OFF/1/2/3/4" fan speed selector is connected to GND, and outputs to a resistor pack to provide speed options, with '4' being direct to motor. The switch also outputs direct GND to AC compressor relay.

At the motor's connector, verify that GND is available at the switch's highest speed setting.
It seems you already verified +12V is reaching the motor.

boxerfan

Did you say that you did indeed find a mouse nest in the old motor? If so it is also possible that the switch or resistor pack is burned up a little. Since 12V is getting to the motor the grounding does seem suspect. Can you connect a jumper wire from the motor negative to the chassis thus bypassing the switch? If you can the motor should turn. Keep your fingers out of there or be prepared to have them whacked a couple of times if you try to spin it up.

The reason we tend to suspect motors is because they are movoing parts. A switch is also a moving part that is rated with a definite life span.