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Heater fan resistor

I have a 2002 Dodge Dakota that I bought about 4 months ago. When I got the truck, the heater fan only worked on high… I knew it was the heater fan resistor and replaced it soon after buying the truck. Now 4 months later the resistor is burned out again. Again I only have high on the fan.
The parts house that I use normally has pretty good quality parts and I have always had good luck with using their parts.
Is this a common problem, because I seem to remember having these burn out early on other vehicles, but that was a few cars and 8-10 years back.

So my question is, could something else be causing these to burn out, or is it normal for ?? 10% ?? to burn our prematurly.


The motor could be dragging a bit, causing it to draw too much current.

It isn;t a common problem.
Remco posits a good theory, as always. If you’re up to doing so, you can remove the fan assembly and test it on the kitchen table with a regular 9V transistor radio battery. It should come to speed easily, quitely, and immediately. If it has to “wind up” to speed, it’s bad. I’ve tested fans this way, and it works.

I’ll check out if I can remove the fan without tearing the whole dash apart. Makes sense about the motor draging. I’ve got jumpers and I might even have a 9 volt around.
Maybe the wifes toys…no, no those are kick start!!!


Ding, Ding, Ding !
Remco Is Probably Correct. I Replaced 2 Consecutive Mopar Resistors Once With New Ones And When I Needed A Third One, A Trip To The Salvage Yard For A “Young” Blower Motor/Fan To Go With The New Resistor, Was The Solution.


You can test it with a 6V lantern battery too. It won;t go as fast, but it still shouldn’t drag.

I have two 6V lantern batteries that I hook up in series to test and work on automotive circuitry on the kitchen table. They’re more than capable of running just about everything in an automobile except perhaps the starter motor and the ignition circuitry.

Why bother with external batteries? Pull the fan/motor, and while you are still at the car, open the hood and use your clip leads to hook to the car’s 12V battery. (Unless it’s too cold out there, and you want to test indoors where your fingers are warm.)

The reason you end up with “hi” only is because it is a DC motor, and to make it go slower at the lo and medium speeds, part of the power is shunted (when you move the speed selector switch) through a series of resistors. So in all speeds, some power goes to the motor, and some to the resistors. The slower you want the motor to go, the less power goes to the motor, and the more power that has to go to the resistor. So the resistor gets hotter at the lower speeds, and burns up faster. That leaves you with no slow speeds and only the high speed.

So what is causing the resistor to burn out? If the motor draws more current than the engineer who spec’s the resistors thought it did, this effect would be worse, and the resistors would burn out quicker. Your problem is either w/the motor itself, perhaps the motor’s winding is shorted out, or the whirling cage or it’s bearing is sticking on something, or there’s just something wrong with the resistors the parts place are giving you. Maybe they are actually for a different car, different year, etc. If you can find a schematic, they usually show the value of the resistors and you can test them with a DVM to see if they are the right values.

Art, the advantage of the external, small batteries is they pose little risk of damage. The car’s battery has an enormous amount of energy capability. You’d most certainly want to include an in-line fuse to prevent accidentally frying the wires or worse in an instant. Also an explosion risk if sparks generated. Why take those risks and extra steps? No doubt someone with experience can probably do it and minimize the risks but when making recommendations to someone of unknown skills or background it’s probably best to keep the risks to a minimum. I’ll venture to say that’s the reasoning behind those recommendations…

Besides, it’s much more comfortable in the kitchen with a fresh cup of coffee, especially when there’s a cold rain or snow outside.

And yup, it allows me to make my errors and test circuits and devices in a safe way. It’s easier to get everything working the way I want it on the kitchen table and then go plug it in.

Years ago, I had a buddy that rebuilt his HD motorcycle engine in the kitchen during the winter. Yep, right smack in the middle of the kitchen table. He was going at the carb with a toothbrush the first time I saw it. His, subsequently ex, wife was not amused. Come to think of it, it may have been her toothbrush. :smiley: Sure looked like a comfy way of doing it!

I realize this is not the same as what you mentioned TSM, but thought you might enjoy the humor of it…

I did enjoy the visual. It brought a smile to my face. Sincere thanks.

You can tell if it is dragging by putting a wire from the battery to the hot wire on the fan motor. You don’t even have to remove it. However, I bet it is dragging.

I took that resistor back and they gave me a fresh one. Now all works fine. They said that they see a few come back and it’s no surprize to have one burn out. Not that it happens everyday.
I don’t have the reciept here with me or I’d tell you the manufacture.

I can out do that one Twin Turbo

In the early 70s a buddy had a Camaro with a 327 that he was rebuilding. I went over to help and he was at the kitchen table Honing cylinders. And his buddy that helped lift the block onto the table was scrubbing parts in the kitchen sink.

I knew the mom pretty well and figured that I’d be safer, if I found some other place to hang out for awhile.

PS. He had to buy mom a new dining room table???