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Thread: front blower mystery-resistor bypass?

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  1. #1
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    front blower mystery-resistor bypass?

    normally when the resistor is shot, the front blower will only work on high. My blower only works on high. However, I bought a new resistor and it still only blows on high.

    The previous idiot...I mean previous owner...altered the wiring for reasons I know not. The resistor wiring is untouched, but the wiring to the blower itself was cut and the connector removed, and an entirely new wire installed that runs to the blower. I'm guessing (and only guessing, because I am not in possession of electrical know-how) that the resistor might be completely bypassed, therefore installing a new one did nothing.

    I know there is also a blower switch somewhere that sometimes burns out, but I've never heard of that causing all of the lower speeds to go out while leaving high speed intact. That's usually resistor. And getting at the switch isn't fun, so I'm not itching to try.

    Given my limited electrical know how, is there a simple way to test whether the resistor has simply been bypassed? If it has i could then contemplate whether I have the smarts to remedy that....I suppose tracing the new wire to the blower might be a first step.

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    Re: front blower mystery-resistor bypass?

    Quote Originally Posted by Previologist View Post
    I suppose tracing the new wire to the blower might be a first step.
    This would be a good start. You may find the original wiring in the process.You could also test for voltage at the resistor itself. Unfortunately, figuring out and fixing other people's "repairs" is typically not a fun job.

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    Re: front blower mystery-resistor bypass?

    Being 4 terminals at the resistor and me having only half a brain, i would need instructions on how to test the resistor connector for voltage. If there were only 2 that would mean i only have a 50% chance of getting it wrong but with 4...thats the wild west, to me.

    I'm pretty sure I saw where the new wire came from while I was doing something else, but I didn't pay close attention at the time. I will check again tomorrow. They also ran it in a different location than the original harness so it should be easy to trace

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    Re: front blower mystery-resistor bypass?

    There are three resistors on the resistor pack each of a different resistance value, one for each of the three lower fan speeds. There is one terminal connected to each of the three low speed outputs of your fan switch. The forth terminal is the ouput to the fan. All three resistors are tied to the output terminal on one side. When the fan switch sends voltage to the resistor pack, it flows through the appropriate resistor and a reduced voltage is sent to the fan. Without knowing which terminal is which, just check all four. Ground your voltmeter negative lead to the chassis and with the fan on any position except high, probe all four terminals of the resistor pack with the voltmeter positive lead. Repeat for each fan speed. If there is no voltage at anytime, it is indeed bypassed.

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    Re: front blower mystery-resistor bypass?

    No power to the resistor connector, as I suspected. I haven't found where those wires originate, and may not be able to.

    I traced one of the new blower wires to the front heater relay. The other one runs under the instrument panel and I presume goes to ground. Still trying to trace it


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    Re: front blower mystery-resistor bypass?

    So here's the setup. One of the new red wires runs from a terminal inside the Front Heater Relay to the blower, and the other new red wire is crimped to a presumably original blue/ wire that is apparently (I can't see) soldered into the underside of the Front Heater (HI) relay next to it.

    relays.jpg

    I couldn't find the origin point of the original wires, although I presume (perhaps incorrectly) that the blue one is part of it. I found no disconnected wires.

    Here is the new wiring from the relays to the blower, seen under the hood. They ran them through the firewall with the cable that opens the fresh air flapper.

    blower.jpg

    And here is the original wiring near the resistor, with the resistor connector intact and the blower wires cut.

    old wires.jpg

    So now what? I can't help wonder why they did this in the first place, and if that holds the key to what to do next. But that might be giving the previous owner, who also owned the shop that did this, too much credit. and I'm not sure I have the electrical skills to fix this myself
    Last edited by Previologist; 09-20-2020 at 08:51 PM.

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