HVAC blower motor resistor replacement

[454cid]

I've got multiple fan speeds that don't work, and a bad control unit, so I ordered new.... severely discounted Dorman control unit through ebay, and a Standard T-series resistor from Rockauto.

I plugged the control unit in, and I still have missing fan speeds, so I bought the resistor.

I've removed the OEM resistor once before, many years ago, but re-installed it..... I think I did it while looking for my non-functioning blower motor problem that ended up being the positive connector right at the motor. I remember it was a pain to do. I think I had to turn the 1/4" drive socket by hand.

Before I change the resistor is there anything to be aware of? Another part I'm likely to need? Watch out not to break this that or the other thing? Make sure I do/don't do this or that?

I probably won't get to it for a few days, but I'm thinking about it now, since the resister just arrived..... also bought a Rockauto t-shirt!

 

[1998_K1500_Sub]

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You might want to check the blower motor and see if it's drawing high current (more on "high" in a minute). Whatever failed in your resister pack may have open-circuited because of above-spec motor load.

I said "high current", above. So... What's high? Well, I don't have a specification but the blower motor in my 1995 S10 pickup draws 16.3A with engine off, blower switch on "high". I couldn't easily measure the voltage across the motor on "high" but I might assume it's around 11.3V.

The intermediate blower switch settings yielded this data, measured at the blower terminals:

Low: 3.1V 2.1A
Med1: 5.2V 4.2A
Med2: 6.7V 6.7A (not a typo, it was 6.7 twice)

The current isn't linear with applied voltage, so don't extrapolate from the data above. In fact, a 2nd-order curve fits it pretty well (pictured)... that jibes with expectation.

For info on those thermal fuses in the resistor pack, see:

Blower motor troubles

I just replaced my blower motor, blower motor reisitor, and the relay on my 95 c1500 a little over a month ago. A week ago it just cut out on me. I have no clue what could be causing it, I tested all the new parts that were installed. The ground to the motor was crusty but still the motor will...

www.gmt400.com

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I had one of the three thermal fuses in the resistor pack fail on my S10, powering the very blower motor measured above. In my case the three lowest speeds would not work. I didn't try to root-cause why the thermal fuse opened, I simply soldered a wire across it and put the resistor pack back in service.

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[Carlaisle]

I recently pulled my blower motor to check the evaporator while searching for the cause of my inadequate AC. Evaporator and condenser were both spotless and charge good so the search continues... To your question, one thing I noticed when I went to reassemble everything was that the hot terminal to the blower motor was discolored as if from an over current condition. Upon inspecting it, I saw that the terminal was very loose...as in so loose I'm impressed it ran at all. It should have been arcing every time I hit a bump but somehow wasn't. If you find this same condition it could be one cause of a high current situation.

 

[454cid]

I recently pulled my blower motor to check the evaporator while searching for the cause of my inadequate AC. Evaporator and condenser were both spotless and charge good so the search continues... To your question, one thing I noticed when I went to reassemble everything was that the hot terminal to the blower motor was discolored as if from an over current condition. Upon inspecting it, I saw that the terminal was very loose...as in so loose I'm impressed it ran at all. It should have been arcing every time I hit a bump but somehow wasn't. If you find this same condition it could be one cause of a high current situation.

Yes, that connector goes bad. That was what I was talking about when I said I mentioned the positive connector right at the motor. I have a regular spade connector there now.