A/C Blower pulling too many volts on high setting??

Discussion in 'Chevy Suburban Forum (GMC Yukon XL)' started by will89, Jul 8, 2009.

  1. will89

    will89 New Member

    Howdy folks. Ive got an electrical gremlin on my 89 Sub that I hope some of you have seen before.

    When I turn on my vent fan to the low or medium settings all is well. However when I turn the fan on to high my charging voltage drops down to about 10.5 to 11 volts. For some reason on the high setting it is pulling way to many volts.

    I have tested the alternator with my voltmeter and it is pushing about 13.5 volts so that is ok. No other circuits, such as light, wipers, etc drain volts like the dash fan does on high. I can even put on about 300 watts of offroad lights and voltage barely drops.

    I first went under the hood to check the relay on the heater/ A/C box and noticed that the positive wire ( from relay to fan motor) was very warm on the end near the relay. The relay itself was not warm at all. All of the grounds appear solid so all I can think to is replace the relay. I want to make sure I am curing the problem though. A bad ground could make this wire heat up right? Or, could it just be that the relay has gone bad.

    I should add that on one occasion the fan shut down after about 30 minutes on high. I will turn back on after it rests a good while. Ive tested the blower motor on 12volts and it runs fine.

    Open to all suggestions...Im sweatin' bullets in this heat
  2. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    Sounds like you're on the right track to me. I wasn't aware that they used a relay on those, but whatever the part that's getting really hot is, is probably your problem.
  3. will89

    will89 New Member

    If I am interpreting the schematic correctly the voltage only pulls from the relay when the fan is set to high. At low and medium setting it bypasses the relay.

    Does anyone know a method to check the grounds using a multimeter?
  4. unplugged

    unplugged Epic Member 5+ Years 1000 Posts

    Is the gauge on the dash accurate? Put your voltmeter on the battery while the ac is on high and compare the readouts. My 93 drops when running on high with no ill effect.

    A good engine to chassis ground is important. You can add a ground using a jumper cable as a test.
  5. Jimmiee

    Jimmiee Epic Member 5+ Years 1000 Posts

    The alternator may show 13.5 volts and still be bad. You need to test it under load. Turn on the headlights, A/C, rear defog, blower, radio and wipers. Run the engine at 2000 RPMs and then read the true charging voltage.
  6. 2COR517

    2COR517 Epic Member 5+ Years 1000 Posts

    I second that, even though you said you can run your offroad lights no problem.
  7. will89

    will89 New Member

    The dash gauge seems accurate as it reads the same as my volt meter. I'll follow up on some of your suggestions and get back to you guys with my findings. Im headed out of town now for about a week. I'll get back. Thanks for all of your help thus far!
  8. will89

    will89 New Member

    Thanks for the tips guys. Ive been outta town since my last post but I ended up getting a relay from the junkyard....and whadduknow? Its fixed!! Thanks again guys

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