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The guy next to me has an inop blower motor that I was helping him with. Complaint was there was some loud banging noise then it stopped working. These are PWM design. He pulled out the cabin filter and it looks like it's been chewed on. Two wires go to the motor and both have b+ on them with the fan speed on high. When I tapped the rocker on the power probe to provide ground, the fan turned on, but clearly has something in it. It seemed to me that the variable motor controller is not providing ground, however, our foreman wanted to know why we were dicking around with it so much and said to just put a test light in place of the motor and see if it shines bright and then dims when you lower fan speed. It did do this, but I'm not sure why I was able to move the fan with the power probe? The only two explanations I can come up with are that the light doesn't draw nearly as much as the fan, especially if there's a rodent in there, and that the probe sends immediate ground where the controller sort of slowly turns the fan on, where maybe it needed a jump to get going?
Would we still have b+ on both sides of the motor if it wasn't turning but jammed up?
Update - there was a giant rodent dwelling in the cage and around the cage. It looked like they had a pillow fight in there. Bench tested fine and worked after everything was cleared out. One thing I noticed and forgot about, is there is a pretty large delay from when you turn the fan on and when it actually starts moving. I wonder if we weren't waiting long enough to see the reaction while testing.
Because it's pulse with modulated, I bet the current is monitored by the HVAC controller.
Rats nest=higher current=no blower.
If that's the case, there may have been a code in the HVAC module?
Were you checking power with the power probe?
I know it's overkill for a blower motor, but maybe the scope would have revealed some activity on the circuit.
Maybe. I was using a PP4 for the voltage tests in the standard voltage mode. Blower motors are pretty common for us so my process it so go right to it with the probe to see if it works then depending on the vehicle I will get out the uscope (perfect for this type of stuff) to make sure there is a signal from like an a/c auto amp. Another reason I want to give the PP Maestro a try.
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