A/C fan won't work on high, fine on other settings
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Joined: Jun 2007
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From: Belleair Bluffs, FL
Another $70 down for a new resistor and that didn't fix it either. I really thought I had it too. The one that I took out had blueish/green corrosion on the terminals from getting wet. It didn't smell fried or anything, but the corrosion definately wasn't normal. I went to a local auto parts store and got a replacement resistor, but it still does the exact same thing. The fan runs on level 2 with level 4 selected, and it's the same on a/c and heat and does not change if I change the ***** at all.
I think I will pull the blower motor out tomorrow night and take a look at that. At least these things are easy to get to. Does anyone else have any other ideas to check?
I think I will pull the blower motor out tomorrow night and take a look at that. At least these things are easy to get to. Does anyone else have any other ideas to check?
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From: Belleair Bluffs, FL
I found this on a Tahoe/Yukon forms, but it makes perfect sense. I'll check it tomorrow. Is there a relay somewhere for me to check other than in the blower motor?
The resistors have nothing to do with the high speed setting, only the slower speeds. The resistors provide resistance in the circuit, dropping voltage to the blower motor to slow the motor speed down. On high, the blower receives full voltage through the blower relay. If you had High but no other speeds, then the resistor pack is usually the culprit.
If you have all other speeds but high, the most common problem is going to be the blower motor itself, relay, or the switch panel. You can check this by turning the fan speed to "high", unplug the blower motor, and check to see that you have roughly at least 12v at the plug. If you have 12v, that means the switch panel is activating the relay and the relay is working. Over time, heat kills the magnetic properties of the magnets inside an electrical motor. Without enough magnetic energy, you may not get enough opposing force to spin the rotor full speed when the windings energize, but still enough to spin at lower speeds.
Another thing you can check is the connector at the blower motor and the switch panel. Sometimes these will heat up, start to deform, and cause a bad connection. The bad connection may be able to handle the lower current draw on low speeds, but the higher resistance from the bad connection won't be able to handle the higher current while in the full speed position.
If you have all other speeds but high, the most common problem is going to be the blower motor itself, relay, or the switch panel. You can check this by turning the fan speed to "high", unplug the blower motor, and check to see that you have roughly at least 12v at the plug. If you have 12v, that means the switch panel is activating the relay and the relay is working. Over time, heat kills the magnetic properties of the magnets inside an electrical motor. Without enough magnetic energy, you may not get enough opposing force to spin the rotor full speed when the windings energize, but still enough to spin at lower speeds.
Another thing you can check is the connector at the blower motor and the switch panel. Sometimes these will heat up, start to deform, and cause a bad connection. The bad connection may be able to handle the lower current draw on low speeds, but the higher resistance from the bad connection won't be able to handle the higher current while in the full speed position.
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From: South GA
That does make sense and I hope you can take that resistor block back to the store. I think if it was a relay then none of it would be working at all. I would pull the blower motor as you mentioned. If you find that to be the issue then go find PCP on DT and get a blower motor from him or find one on ebay.
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From: Belleair Bluffs, FL
I checked the voltage going to the blower motor and that was fine. It's around 10vdc with the fan **** off and around 14vdc in all other settings. I hope there's something in the blower motor itself, if not, I'll be chasing this gremlin for a while. We may be trading the truck in, so I may just leave it. Off to the store to try and return the resistor block.
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I know I am resurrecting a very old thread but I just wanted to share how I fixed this problem. I was having the exact same problem with all the speeds working except high. It would run on high for a short while then cut off and feel like it was running on low or less. I replaced all the parts that have to do with the blower motor. Started with the resistor then the motor it self even a used hvac control panel from ebay since my local junk yard did not have any. Today I got out my multi meter and figured out it was the ground wire that was the problem. I was just going to splice into it and ground it better so I removed the passenger side kick panel by the blower motor and saw the thicker blue wire with yellow stripe that I figured was the ground plugged into a connector right there. I pushed the connector together it only went together a 1/16 of an inch or so more but it made a difference. zip tied it together so it would not come loose again and I am now a little more ready for this texas summer.
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From: Clayton MI
Supposed to be in the 90's for the next two weeks here.... I am REALLY thinking about addressing the a/c in my truck. It hasn't worked since I owned it. (about 3 years..... no point rushing into anything, right? 
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