Question about 1999 GMC Suburban

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99 Yukon - Blower Motor Not Working

Hi ... Having issues with blower fan on 99 GMC Yukon … hope there are some experts out here that can help.

99 GMC Yukon SLT 4WD – Front and Rear AC

Issue: Drove the truck to destination and blower worked fine when truck was shut off. Got in it to leave and turned on heat on but no blower. Blower does not run in any of the four positions of the Control Switch. I have checked fuses but all are good. I originally suspected it was the blower motor but now am stumped!

Took the fan motor out and tested voltage. Here's what I saw which, to me, is strange.

There are four ''knotches'' on the rotary switch corresponding to fan speed ... right? Defined in the schematic as Lo, M1, M2 & Hi. Below is the voltage I see at each setting using a digital meter.

Off - Zero Volts
Low - 8v but climbs slowly to about 9v
M1 - 11.7v
M2 - 11.45v
Hi - Zero Volts
Note: When I turned to a lower setting from any higher setting the voltage drops dramatically and then slowly climbs back to the values from above.

I have now replaced both the Fan Motor, the High Blower Relay with no avail or change in voltages.

I removed the Blower Resistor and check for continuity across all of the various coils and the one resistor. All are good.

The only thing I have not replaced/tested is the HVAC Control Module which includes the rotary switch.

Other notes:

I have checked wiring harness around the heater housing for signs of overheating. No visible signs.
Change other rotary switch for air deflection and the appropriate doors open or close. I can hear them.
The Recirculation button works fine as I can also hear/see the door operate.
Rear AC fan works fine.

Questions:

1. I understand a common problem is that if the resistor goes bad, the fan may only operate on Hi. I am seeing the opposite. Should I be seeing continuity across all poles on the resistor?
2. Couldn’t I hook the fan to a 12v power source and it should run? Haven’t done it yet, afraid of frying the brushes but seemed like a basic test.
3. Should the HVAC Control Module be the next focus? Is it a pain in the **** to remove?
4. Am I delving too deep here and missing something obvious?

So I'm somewhat stumped. Wondered if anyone you had any specific recommendations based on the above info.

Thank you in advance ... hope you had a great Thanksgiving.

RG

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  • Anonymous Dec 28, 2008

    same

  • Anonymous Jan 24, 2009

    I have the same exact problem, my blower was working on a very cold morning, then all of a sudden it went out and has not come back on. I have change almost everything dealing with the heating and cooling system. Expect the blower.

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I went through the same thing with my 99 suburban. It turned out to be the dash fan control switch. It is purchased seperate from the whole cluster for under twenty dollars. The instrument panel cover comes off gently by hand with the tilt steering in the down position. You have to then unplug the electrical plugs to get it out of the way. The heater ac control panel then comes out by hand far enough to unsrew the heater fan control from the back.

Posted on Jan 24, 2009

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If you have already changed the blower motor, than ignore my comment. My 99 Suburban blower didn't work on low speed, only medium high and high. I thought it was the resistor pack, so I changed it. The low speeds then worked, but I quickly noticed a burning smell at the two lowest speeds. I turned it off quick not to burn up the new resistor pack. I noticed one terminal of the fan switch wire connector looked to have gotten very hot in the past. I changed the fan switch but no change in symptoms. Still smelt like burning at low speeds. The motor appeared to work fine durning all this, but with nothing else to try we swapped out the motor for a new one and that sloved all the problems. The original motor was wearing out and though running fine was pulling to many amps through the fan switch and resistor pack. For those that haven't replaced the blower motor yet, I'd advise doing this as preventative maintaince so you don't burn up the resistor pack, fan switch, or wiring.

Posted on Dec 21, 2009

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The power supply in the blower circuit feeds to the blower first so at the blower there should be 12 volts at the feed line. I think purple. Power then goes thru the resistor to the blower switch. By pulling the switch and checking the wires from the resistor you should have power on each one. Then there is a ground that comes off the switch to complete the circuit. Make sure that this is a good ground. Sometimes the harness connector on the back of the switch gets burned. You can hook the blower to a 12 volt source, just put a 20 amp inline fuse in the wire.

Posted on Dec 01, 2008

  • SM124 Dec 02, 2008

    I checked the wrong diagram. It feeds thru the switch first, then the resistor, then the relay to the blower. If you have the voltage on the ground side of the motor you have a bad ground. Try running an extra ground wire just to see.

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I have been back an forth on this site several times and for MY issue it finally helped me fix it. I started with the issue of the blower only blowing on high no matter what the setting....I replaced the resistor and no change. It would never shut off in off mode though? (That should have immediately prompted a replacement of the switch). I then ended up with the blower NOT RUNNING AT ALL OF COURSE ON THE COLDEST DAY OF THE WINTER SO FAR. I did a circuit test at the purple wire and was boggled because I had power to the line through all BUT HIGH? Weird that the low was actually the highest voltage? I then replaced the blower motor because it appeared to be the next step but still no change. I switched out the relay also... NO CHANGE. Finally, I replaced the control switch. VOILA!!!!! Now I have all my speeds working well, a VERY TOASTY-WARM SUBURBAN, and a happy wife. In reflection I would say that if you have the same issues that I did at the front....then start with the control switch first and work past that. ALSO be very aware of the wiring behind the control switch (I taped a short on a wire while replacing on the dash).
All in all here is the cost...Resistor $16, Blower Motor $49, Relay $20, Control Switch $20....Heat in family primary grocery getter...PRICELESS!!! But like I said before. If this occurred again in another truck I would start with the switch and move from there. I do think that my Blower Motor needed replaced anyway just to be safe, my resistor was bad at some point... But I think the relay was not needed. All this was relatively easy to replace (worst was resistor just because of tight fit.) Do no lose heart. You can complete it just keep going. AND IF POSSIBLE BORROW A HEATED GARAGE TO FIX IT.

Posted on Dec 30, 2012

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