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What are the specs of the thermal fuse in the blower motor resistor?


kxri318

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The fan was only working on high in my 1986 Ford Ranger and I read that it could be caused by the resistor itself or corrosion in the connectors. I checked all the connections and they're all 100% corrosion free, so I tested the actual thermal fuse on the resistor itself and the fuse is blown. Does anyone know the specs of this fuse? There are 0 marking on it at all, its just solid black.
 


franklin2

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This link says 121 degrees C for the value.

 

kxri318

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This link says 121 degrees C for the value.

Yeah I saw that too but that's for a 98 explorer. Wasn't sure if mine was slightly different or not.
 

franklin2

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I have done several where I just used a jumper. I do not know the purpose of them, I have seen many stories of the resistors catching leaves in the heater box on fire and melting it. The thermal fuse did not do anything to prevent that.
 

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I have done several where I just used a jumper. I do not know the purpose of them, I have seen many stories of the resistors catching leaves in the heater box on fire and melting it. The thermal fuse did not do anything to prevent that.
If only our trucks had cabin air filters.... every spring I have to pull my blower motor out and clean the leaves out of the housing. That noise of the leaf rubbing on the fan blade drives me INSANE.
 

franklin2

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The resistor is downstream of the fan were the airflow from the fan keeps the resistor cool, it gets red hot in normal operation. When the leaves enter and are still flexible, they can make there way down onto the resistor and hopefully it will just smoke you out of the cab. The worst case it catches fire.
 

RonD

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120degC is 250degF and its not a "fuse" but will melt and separate like a fuse if it gets hotter than 250degF

These "blow"/separate based on temp only not AMPs
Regular fuse "blows" based on AMPs and temp

Yes, 120degC would be correct for these in pretty much any year Ford
 

Josh B

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A friend had a 94 that caught fire and burned. Not long after I was headed to town and turned on the heater/defroster and soon smoke was coining out my vents.
I shut that thing plum off and luckily it didn't go any further. Soon as I got home I cleaned all the duct work, and also put screen wire across any openings anything could get through, inside and out
 

kxri318

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I bought a pack of 121c thermal fuses for a couple bucks and put one in. It works great now on all speeds, thanks a ton.
 

kxri318

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If only our trucks had cabin air filters.... every spring I have to pull my blower motor out and clean the leaves out of the housing. That noise of the leaf rubbing on the fan blade drives me INSANE.
When I removed my AC (previous owner mangled it) and threw in non-ac air ducting, it was completely packed full of leaves and honestly I was surprised it hadn't caught fire yet. Good to know that's something I should check more often though
 
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