Blower resistor testing 89 BII
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Cross-Country
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Blower resistor testing 89 BII
Are there any tests on this resistor? I have run some continuity tests and it shows closed circuits. The control switch tests sat. Have voltage. However the fan only runs on high speed.
Elder User
Joined: Feb 2006
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From: SE Michigan
When testing the resistors we need to know the resistance values of each winding. A continuity check will usually check good but the value is what makes the fan speed different at each setting. I would still suspect a bad resistor pack, especially since it runs the fan on only the high speed. That is kind of the default setting when the resistors go bad. They're kind of inexpensive ($15 or so)and easy to get to for replacement.
Posting Guru
Joined: Sep 2004
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From: Yokosuka, Honshu, Japan
I agree with Stan, to check the resistor bank properly, you need to know the values of each tap on the bank - and generally speaking, if the fan only works on high speed, it's usually an indication that the resistor bank is bad/shorted. Relatively inexpensive and easy fix.
Cargo Master
Joined: Mar 2007
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From: Arcadia, Fla
Take out the resistor block and on it you will see a small thermal overload type fuse inline with the resistors. That is most likely open and then you will only get high speed. I replaced it with a jumper and never had problems with it. I did the same thing to my 84 F250 almost 18 years ago and it still works. Make sure to clean out the area from crud that could burn too.
The resistance of those things are going to be under 1ohm so most meters will not read them correctly
The resistance of those things are going to be under 1ohm so most meters will not read them correctly
Posting Guru
Joined: Sep 2004
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From: Yokosuka, Honshu, Japan
Only problem with that fix, Eddie, is that if something ever gets in the blower box and the blower motor hangs up and overheats, you'll have one interesting electrical fire to deal with! I only suggest such things as a temporary fix until the replacement part can be installed....
Cargo Master
Joined: Mar 2007
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From: Arcadia, Fla
Thats what the 30 amp fuse is for.
The thermal fuse if was for the motor overheating would be mounted directly on the moter itself as high speed current doesn't got through that fuse. Some vehicles don't have that thermal fuse at all. Most likely the fuse was designed for when crap inside the duct catches on fire it turns off the current for the lower speeds.
The thermal fuse if was for the motor overheating would be mounted directly on the moter itself as high speed current doesn't got through that fuse. Some vehicles don't have that thermal fuse at all. Most likely the fuse was designed for when crap inside the duct catches on fire it turns off the current for the lower speeds.
Posting Guru
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From: Yokosuka, Honshu, Japan
Eh, s/overheats/overcurrents. That 30A fuse will pop.... eventually.... under the circumstances, but you may also burn all the wiring in between in the process 
I've only seen a few DC motors with thermal overloads in the windings that I can recall, and the blower fan motor is nowhere near the type of service where you'd see that. I say replace the resistor pack part, check the airbox for debris and clean it out if necessary, and be done with it. *shrug*
I've only seen a few DC motors with thermal overloads in the windings that I can recall, and the blower fan motor is nowhere near the type of service where you'd see that. I say replace the resistor pack part, check the airbox for debris and clean it out if necessary, and be done with it. *shrug*
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update
Went to pick n pull, for $1 I got 3 resistors, in case two were bad, and a couple of fan speed switches. Runs on all speeds now. thanks for all the help out there. BTW, one reason I sorta did not suspect the resistor at first was that I could not locate 12v dc at the resistor plug.
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