Why won't this work!? (heater resistor pack) - Toyota Nation Forum : Toyota Car and Truck Forums


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Old 03-28-2009, 02:08 PM   #1 (permalink)
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Why won't this work!? (heater resistor pack)

'87 SR5, 4speed fan
Alright, so I finally decided to mess with my fan resistors since I lost my two low speeds a while ago. I followed this website can removed the resistor pack:

http://www.4crawler.com/4x4/CheapTricks/Blower.shtml

The two bad resistor coils broke close to the soldering point, so I tried resoldering them. This worked for a few days and I was able to enjoy my low and medium-low speeds, but they burned up again. The coils looked pretty bad and there was no saving them.

Then I got an idea before going out and buying a replacement Since the 3 resistor coils sort of act like a manual potentiometer (controlled by the heater switch), why wouldn't replacing the bad resistor coils with regular, carbon film resistors of equivalent resistor values work?

I measured the resistance of the bad coils and they were really high, over 1Mohm each. The good coil which controls the high speed fan was only a couple ohms. Well, just to experiment, I installed a 40ohm resistor and 100ohm resistor in place of the bad coils. Plugged it in and couldn't get anything. I was puzzled why it wouldn't work. Even if it was a power handling issue I'd at least blow up the resistor or see some sort of response.

I verified all positions of the switch is working by short circuiting the resistor pack for each switch location. So I could go through low-med1-med2-high and they would all give me the high fan response (since there is no resistors reducing the current through the fan).

Only thing I could think of is the resistors I used were still too high...but I don't have a new resistor pack to measure the resistance. I haven't got a chance to mess with it anymore but I could go get some resistors of lower values and try them (40ohm is the lowest I have on hand). There may be a power handling issue with the resistors since they are only 1/4 watt, but still I should see something happen since I am completing the fan circuit.

Any ideas? Yes yes I know...just go buy the replacement. But, I like to tinker around and now that I have this problem its bugging me
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Old 03-28-2009, 05:56 PM   #2 (permalink)
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I'm not an expert so this is just what I've found on my own. They were .4, .8, and 1.5 ohms on the vehicles I've checked. However, regular resistors won't work from my experience. Too many amps. And the hi watt ceramics are too large to fit. May be able to use nichrome wire but by the time you buy it you'll likely have more money tied up than replacing the part. Good luck.
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Old 03-29-2009, 12:05 AM   #3 (permalink)
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Concur with Dave.
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Old 03-29-2009, 12:40 AM   #4 (permalink)
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You might want to check the commutator on the motor itself. I lost my lower speeds as well, and it turned out that the brushes had worn the comm down a good 1/8". Replaced the motor and it worked fine.
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Old 03-29-2009, 02:00 AM   #5 (permalink)
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Thanks guys for the help. Makes sense. I knew the power handling of the resistors would be an issue but I was just puzzled why I couldn't get any response with the setup I had...I must have had too much resistance.

DCM, its definitely the resistor pack.
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Old 03-29-2009, 07:38 PM   #6 (permalink)
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^Okay, just one more thing to cross off the list...
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Old 03-29-2009, 08:11 PM   #7 (permalink)
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The resistance of the resistors (aka coils in this case) is very low, and the current capacity is high, that's why your experiments didn't work.

If you could find discrete resistors of the proper resistance and wattage, they would work. But that's a long shot.

Your better off buying the new part from Toyota (and that's not something I usually say).
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