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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 I have Nissan N16 2000 model car. My blower is not working....I tested the motor direct( its working)....but when i use blower switch nothing happens....neither speed 1 ,2 or 3 and Automatic mode is working.....seems like my blower switch is giving problem can someone help plizzz

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Replace the A/C control head... very simple to do. Pop off the dash panel and pull the control head out... unplug the 3 harnesses and there you go.

Posted on Jun 20, 2009

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SOURCE: 99 Yukon - Blower Motor Not Working

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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