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05 Yukon a/c fan issue

azwildcat on Wed May 29, 2013 3:42 PM User is offline

Year: 2005
Make: Gmc
Model: yukon
Engine Size: 5.3

I am having issues with my front AC fan operating at high. The rears work perfectly fine. But when I have the front fan on high, it will go between about 10 percent and then jump up the full blast intermittently, going back and forth every few minutes or so. temperature is not an issue. The controls are electronic. Do you think my issue is a control issue, or could it possibly be the fan/motor and or resistor? Thanks for any advice you can give!

mk378 on Wed May 29, 2013 4:59 PM User is offline

Measure the voltage across the fan motor terminals when it is running slow (motor still plugged in). If you have 12 volts but it is turning slow, motor must be bad. Otherwise it is probably the amplifier. This should be a system where the motor gets constant 12 volts on one lead from the underhood fuse box, and the amplifier pulls the other lead to ground to make the motor run. There is no resistor. The amplifier pulses the lead to ground, the longer the pulses are, the faster it runs. If you unplug the amplifier and connect the two big wires (motor and ground) together in the plug, the motor should take off at full speed.

azwildcat on Fri May 31, 2013 10:56 PM User is offline

azwildcat on Fri May 31, 2013 11:05 PM User is offline

So I kinda tore it apart. It does have a resistor. The control unit shoots a positive / neg / and input lead to the resistor. Then out of the resistor to the fan is only a pos and neg lead. My voltmeter is not giving me any reads, so it's bad, i'll pick up another tomorrow. When I hit my test light on the "input" lead, it's brightest when I select the low speeds and gets more dim as I turn up the fan speed. There are definite steps in the amount of brightness from low to high and then back down. Why is this?

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