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GM / General Motors: Rear defroster not working.

  1. 10-20 05:48 PM #1
    Marc
    Guest

    Rear defroster not working.

    Good afternoon.

    The rear defroster in my girlfriends 2000 Olds Alero no longer works.
    The light on the button comes on, but nothing happens out back.

    All of the fuses in the dash and under the hood are okay. The relay
    was swapped out with an identical one from another circuit... like
    the blower motor or something. No go.

    Testing the voltage on the leads, is where things get weird. In all
    tests, the car was running and the defroster button was lit:

    - Leads disconnected. Attach volt meter. I see about 13 volts.

    - Attach leads to heating grid, the voltage drops to 0 with a tiny spark
    upon connection.

    - Disconnect leads from window, and I can watch the voltage rather
    slowly climb back up to ~13v. (About the speed the counter on a gas
    pump operates.)

    So from what I'm gathering here, it "looks" like some sort of a
    capacitive circuit is tied into the defroster.

    The only thing that has changed with the car, since the last time the
    defroster was operated (approximately last spring or so), was that the
    blower motor fan/speed control on the dash was not operating correctly.
    A shop replaced a resistor up under the dash. I forget the exact name
    right now. Was it a balast resistor?

    Is there more to the defroster circuit than just a button tripping a
    relay to power the heating element?

    Should I dig into the dash, to make sure everything conected securely
    behind the temp-control section?

    Any other idea's where I can stick my hands?


    Thanks for your time,
    -marc
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  2. 10-20 11:28 PM #2
    David
    Guest

    Re: Rear defroster not working.

    Make sure the ground wire out of rear glass has continuity to the body.
    "Marc Westerlind" <com> wrote in message
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  3. 10-21 06:00 PM #3
    Marc
    Guest

    Re: Rear defroster not working.

    David J and Lynne J Shepherd wrote: 

    Will do... Thanks.

    I also hear there is some sort of a defroster / antenna module
    back there. I'll have to pull apart the molding and check things
    out.

    -marc
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  4. 10-22 01:52 AM #4
    Bobo
    Guest

    Re: Rear defroster not working.

    When you pull the plastic panel back on the rear of the car and find the
    antenna module(rt side), the big black wire going in, then out to the rear
    glass will be melted ,probably on both sides... No you can either replace
    it, and find replacement connectors(almost impossible), or try the fix
    below..
    simply splice in before and after the module with a wire as large as the
    wire there..the current will bypass the module, but the radio can still use
    th grid as an antenna...I know it's not right, but it works, and saves a
    bundle.... Bobo
    "Marc Westerlind" <com> wrote in message
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  5. 10-22 04:10 AM #5
    Harry
    Guest

    Re: Rear defroster not working.

    when you say you swapped out the relay with another, do you mean the 30
    Amp Circuit Breaker in the fuse box ?

    =========
    Harryface
    =========

    1991 Pontiac Bonneville LE
    ~_~_~270,000 miles_~_~_




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  6. 10-22 06:53 PM #6
    Marc
    Guest

    Re: Rear defroster not working.

    Harry Face wrote: 

    I'm not...too...sure...

    I'm 99% sure what I swapped was a relay. Little 1.5"x1.5" plastic
    grey box. Some long part numer, maybe 7 or 8 digits. The four
    terminals in the botom work in a cris-cross patern. One way is
    open, the other I get a short. I could have sworn there was a
    schematic on the bottom or on the side or something.

    Where would I find the circuit breaker that you mention?

    -marc
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  7. 10-22 06:54 PM #7
    Marc
    Guest

    Re: Rear defroster not working.

    Bobo wrote: 

    Awesome! Sounds like this is the problem here...

    Thanks,
    -marc
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  8. 10-22 08:52 PM #8
    Harry
    Guest

    Re: Rear defroster not working.

    30 Amp Circuit Breakers are little silver rectangular, tin boxy looking
    things plugged in the main fuse box inside the car. They press in just
    like a regular fuse.

    Generally, the Circuit breakers covers Rear Defroster, Power Windows,
    Sunroof, Convertible Tops, Door Locks and Power Seats.

    Seat, Door locks & Defroster are on the same breaker in my car. The
    second breaker I got covers the Windows and Sunroof ( If I had a sunroof
    ).

    =========
    Harryface
    =========

    1991 Pontiac Bonneville LE
    ~_~_~270,000 miles_~_~_




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  9. 10-24 02:41 PM #9
    Marc
    Guest

    Re: Rear defroster not working.

    Harry Face wrote: 

    Okay, I could have sworn I saw them, but didn't bother with 'em.

    I'll check them out just to be sure... but everything else in the
    car seem to work good, so I'm not too sure.

    Thanks,
    -marc
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  10. 10-29 01:40 AM #10
    451ctds
    Guest

    Re: Rear defroster not working.

    Did you check the ground ? Run a jumper from a known good ground, just to
    be sure.


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