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Thread: blower fan circuit wiring 90 SC

  1. #1
    Join Date
    May 2002
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    blower fan circuit wiring 90 SC

    I have a problem with my interior blower fan on a 90 sc. It doesn't operate. Here's what I've checked so far:

    - Fan motor itself (applied power to it directly and it works fine)
    - checked the resistor pack in the case.. its fine as well.
    - swapped both the motor speed swicth and the a/c selector switches on the dash.. no fix.
    - checked the 80A fuse under the hood.. its fine.
    - checked the 30A fuse under the dash.. its fine.
    - swapped the ignition switch.. no change

    So what I'm left with appears to be a wire issue somewhere, but I don't have any good wiring diagrams for that.
    My factory manual doesn't cover it, nor does the Haynes book. I have a complete but difficult to read Chilton's diagram,
    but my eyesight isn't good enough for the microscopic print.

    Does anyone have a circuit diagram, or insight, ideas that they could share?

    TIA

  2. #2
    Join Date
    Dec 2007
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    Salem OR
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    I'll look thru my '90 EVTM, but in the mean time - done any work lately, when did it work last, anything aftermarket in the dash such as radio, gauges, etc., any other circuits acting out?

  3. #3
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    Quote Originally Posted by KMT View Post
    I'll look thru my '90 EVTM, but in the mean time - done any work lately, when did it work last, anything aftermarket in the dash such as radio, gauges, etc., any other circuits acting out?
    Nothing lately. It was working until late summer, after my daughter started driving it. I seem to recall the smell of something electrical melting a few months before, but it went away and I didn't have any problems later on. I sort of dismissed it.

    I didn't see anything obvious at the switches, nor with the connectors.. such as scorching.. and the resistor pack looks almost new. no rust.

  4. #4
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    Dec 2007
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    Power goes from the PCB/blower fuse to the heater~A/C control selector switch. It leaves that component and goes to the motor, then thru the blower switch, then thru the resistor pack depending on speed, then from either of those to ground.

    I'd light the heater~A/C power circuit, then blower switch on high (bypasses the resistor pack), and do voltage checks, starting at the motor.

    If you have power to the motor, check for power at the blower switch. If you find power there, check that circuit's ground...inside dash, near the steering column - you'll need to pull the bezel and steering wheel trim. I think it's above and just to the right...only small wire ground in that area, should be obvious, but that ground is also for other things, such as the VMM, so if it was compromised, you'd see issues with other circuits. You can still check for continuity from the motor/blower switch pack to that ground, tho.

    If you don't have power at either the motor or the resistor pack, check for power at the switches, if power there and the ground ohms out ok, the issue is in the harness between them.

    There are other areas to check, depending on what you find to this point, but since your issue seems atypical, meaning not the normal fuse/motor/switch/resistor pack issue, you'll need to work the problem by verifying circuits. If you've replaced parts, that means you've moved the harnesses around, so something like a weak connection at a connector should have surfaced then, hopefully, but you may need to do a closer inspection for damaged wiring/connectors.

    Yell if you need wire colors to help do checks...
    Last edited by KMT; 11-11-2019 at 03:27 PM.

  5. #5
    Join Date
    Jul 2005
    Posts
    457
    Good morning

    Take another look at the blower motor switch connector. The orange/black wire has probably burnt the surrounding connector housing and or speed wires. The clue I believe is your third post with the burning electrical smell. I have had the same fan discrepancy on a 1989 LX and 1990 SC.


    If evidence of overheating replace the connector.

    Check fan motor for amp draw with the switch selected to HIGH.



    In my case both the 1989 LX and 1990 SC blower motor switch connector and fan motor were replaced.

  6. #6
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    Quote Originally Posted by sam jones View Post
    Good morning

    Take another look at the blower motor switch connector. The orange/black wire has probably burnt the surrounding connector housing and or speed wires. The clue I believe is your third post with the burning electrical smell. I have had the same fan discrepancy on a 1989 LX and 1990 SC.


    If evidence of overheating replace the connector.

    Check fan motor for amp draw with the switch selected to HIGH.

    In my case both the 1989 LX and 1990 SC blower motor switch connector and fan motor were replaced.
    I'll definitely take another/closer look at it. Thanks.

  7. #7
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    Well it turns out that the selector switch was the problem. I had tested with a 2nd one that was also bad. Found out that I had forgot to replug in the motor itself when I tested it originally, discovered that while tracing the wires, and applying power through the connectors.

  8. #8
    Join Date
    Dec 2007
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    Salem OR
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    Owner 1, two bad switches 0 ...good job, thanks for the wrap up.

    Ken

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