No power to blower fan randomly

Jimmy0219
0

Asked by Jimmy0219 Jul 29, 2012 at 05:49 PM about the 1999 Pontiac Bonneville 4 Dr SLE Sedan

Question type: Maintenance & Repair

The AC blower fan works fine when it has current, but sometimes, inexplicably,  there is no current to the motor.

I've replaced the blower motor twice in this car since we got it 8 years ago, last replacement was about 4 months ago.

Scenario 1: Car is off, no key in ignition, AC is set to MAX and fan on high.  Insert key, turn to ON position (not start yet).  The blower fan should turn on, but about half the time it does not.  There is no pattern as to whether it will work or not.

Scenario 2: Car is running, AC is off.  Setting AC to MAX --  about half the time the blower motor doesn't work.

Scenario 3: Car is not running but ignition is in the ON position.  AC is set to MAX, and blower motor is running.  Turn key to start the engine.  Sometimes the blower motor stops running at this point.  Sometimes cycling the AC control to Off and then back to MAX will make it start working.  Sometimes it takes several repetitions of this to get it started.

I hooked up a volt meter to the AC blower fan at the point where the power wires connect to the fan itself.  In all scenarios when the fan should be running, there is no current directly at the motor.  If this was just a problem with the blower motor, I would expect current to be present.

Any help would be greatly appreciated.

Many thanks,
Jim

5 Answers

dynasg2009
1,115

Hey Jim, I think what you might try is to check the actual fan switch or the blower motor resistor. I have seen on those cars the fan speed selection switch is bad. If you have the automatic climate control then the entire unit needs to be replaced in the dash. Hope this works.

Jimmy0219
0

Thanks dynasg2009. After reading your response, I replaced the resistor but this doesn't seem to have made a difference. Also, the fan switch doesn't seem to be the problem because when I touch the connectors directly together (bypassing the switch) it does the same thing... the fan only turns on about half the time. Sometimes when I turn on the AC, I can hear the blower fan start to turn for just a moment, but then it stops (I can hear it spinning down). Thanks again... any other ideas would be very appreciated. Would it help if I post a video on Youtube showing how the fan only seems to start about half of the time? Jimmy

dynasg2009
1,115

Ok, What you could have done first as mentioned above before changing out the resistor was to check the plug on the back of the control head or unit in the dash. If you are able to remove the control unit where you turn the fan speed selector and test the back of the plug while plugged into the control unit. There you will be able to watch the voltage and see if or when it drops out. I am sure it looses power on any fan selection you chose and that is the only other thing in that line that would cause the fan to stop. The fan is new, resistor as well and the only thing to check. Each wire on the plug that's plugged into the fan speed control is a different speed. Just find one and test it till the fan shuts off and try other speeds as well. I have found the fan selector switch on GM products failing more than any other component in the A/C system.

2 out of 2 people think this is helpful.
Jimmy0219
0

Sorry, maybe my earlier explanation was a bit lacking. I did of course test the fan switch before replacing the resistor and could not find anything wrong with it. The results are the same whether I use the switch or bypass it. Same with the fan speed control switch. The fan only starts about half the time, particularly when the car is cold. It seems to work better after the AC has been running for a few minutes.

dynasg2009
1,115

The only other thing I could think it could be is a bad or intermittent grounding problem. Just for testing purposes you might try to add an additional wire to the ground side of the fan motor and run it to a ground under the dash and see how it runs then. If it runs fine then you will have to trace the problem down and repair it or if you can find a junction somewhere in the ground wire and just add an additional ground to make the fan function properly.

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