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Rear window defroster 850 1997

posted by  someone claiming to be JimP on  Sun Nov 3 04:40 CST 2002 [RELATED]

On a 4dr sedan how do I trouble shoot a rear window defroster? I don't think the mirror defrosters work either, so it should be something systemic. Fuse is OK in slot 28.

What do I do next?








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    Rear window defroster 850 1997

    posted by  Mechanic on  Mon Nov 4 06:27 CST 2002
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    Do you have a (VOM)volt-ohm-meter ? Put your VOM on DC volts,and then turn on the rear de-fogger switch and then chk. for 12v at the wire that connects to the window grid.... if it is hot(12volts present) then switch off your de-fog switch and switch your VOM to Ohms. Put the two meter leads across the defogger grid itself. If meter shows some low resistance, then you know that the actual grid is Ok. So,if you have 12v., and a good grid, then the only thing left is the return path.. which is the ground. Check to make sure that that return wire has continuity to ground. BTW, Radio Shack has very inexpensive Digital VOM's starting at $10. I have a larger one in the shop and a small folding one that I keep in the car tool box. Tom








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      Rear window defroster 850 1997

      posted by  JimP on  Mon Nov 4 08:41 CST 2002
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      I do have a tester. The only problem now is how to locate the wire that goes to the grid. It is probably behind the panels on one of the rear pillars. the panels look like they require removal of the headliner as well. Do you know an easy way to get to the connection?

      The sequence of testing makes sense to me once I get to the grid connector.








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    Rear window defroster 850 1995

    posted by  HO on  Mon Nov 4 02:11 CST 2002
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    last visit: Tue Aug 12 14:01 CST 2014
    [RELATED]

    Jim,

    I have the similar problem with the rear defogger not working very well but mirrors are fine. My car is a wagon, so the connector of the defogger is located in the driver side D pillar. The connector provides the +12V and GND pins to the defogger wire. The GND is connected to the car body via a metal screw. I am not sure about the sedan setup. Hopefully, it is similar to wagon. If the switch is good, then you can check the relay. The relay is the heart of the heating circuit. Both mirror heating element and rear defogger heating element are come from the same +12V source inside the relay but 2 different pins out of the relay.

    Hope this help.

    Ching-Ho Cheng
    --
    1995 855 NA, Bilstein Shocks, K&N Filter, E-Code Lens








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      Rear window defroster 850 1995

      posted by  someone claiming to be JimP on  Mon Nov 4 02:48 CST 2002 [RELATED]

      HO
      Thanks for the info. The rear pillar trim looks like a major job to remove so I will check the relay first. Where is it located? Any identifying features? I have a wiring diagram for the defroster system, but it does not give any locations of course. It does clearly show the separate pin for power to the rear defogger. This also explains why the mirrors and pilot work on the switch: they all get their power form the same pin.

      Thank you for your insight and help.

      Jim








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        Rear window defroster 850 1995

        posted by  HO on  Mon Nov 4 04:18 CST 2002
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        last visit: Tue Aug 12 14:01 CST 2014
        [RELATED]

        Jim,

        The relay is located right above the driver side knee bloster. Once the plastic bloster panel (undert the steering wheel) is off, and look up from the driver side foot well. The group of relays is near the A-Pillar area. It is a crowded area with bundle of wires. It doesn't has much room to work around. My hand is small such that I can go in without any problem. Otherwise, you need to remove the metal knee bloster to gain access to the relays. I forget the relay number. I need to look it up and let you know tomorrow, if you don't mine.

        Ching-Ho Cheng
        --
        1995 855 NA, Bilstein Shocks, K&N Filter, E-Code Lens








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          Rear window defroster 850 1995

          posted by  JimP on  Mon Nov 4 05:10 CST 2002
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          Ho
          Thank you again. Of course I will wait if you are kind enough to look up the number. Also, if there is a place for me to get this info, feel free to re-direct me to it.

          Once I locate the relay, I assume a voltage test at the pin is in order. If it is bad I replace the relay right? If that is OK, I assume a continuity test from the pin wire (disconnected) to ground is the next step. If that is bad I know I am into tracing. If it is good, then what?

          You have been very helpful. Thank you very much.

          Jim








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            Rear window defroster 850 1995

            posted by  HO on  Mon Nov 4 16:58 CST 2002
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            last visit: Tue Aug 12 14:01 CST 2014
            [RELATED]

            Jim,

            The relay number is 208, located in the 2nd row counting from the top. There are 3 relays in the 2nd row. A big one (205 & 206) starts from the left hand side. 207 is in the middle and 208 is the last one in this row. Relay's Pin 3 is the output +12V to the defogger, while pin 4 provides the +12V to the defogger switch and the heater element of the side mirrors. The +12V connects to the grid on the drive side's C-pillar while the ground connects to the grid on the passenger side's C-pillar. The wiring is on the driver side from relay to a connector (behind the headlight switch and goes to the heating element in the rear window.

            Hope this help.

            Ching-Ho Cheng
            --
            1995 855 NA, Bilstein Shocks, K&N Filter, E-Code Lens








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              Rear window defroster 850 1995

              posted by  JimP on  Tue Nov 5 09:16 CST 2002
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              Ho
              Thanks for the detailed info. I will check it out and if all is well move on to getting the plastic molding off of the C pillar.

              Your assistance has really been appreciated. Thank you.

              Jim








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                Rear window defroster 850 1995

                posted by  JimP on  Fri Nov 8 15:41 CST 2002
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                Thanks to all who supplied help. It was a loose ground. I never completely removed the molding from the C-pillars but was able to pry it back enough to get to the connectoors. For future reference slip your fingers under the molding about 2 inches from the top and bottom to snap it loose and gain about an inch of room to work. Pulling from the center may crack the molding (duh)but it reseals itself when you push everything back.

                Thanks again.








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    Rear window defroster 850 1997

    posted by  danielflading on  Sun Nov 3 07:36 CST 2002
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    CHECK FOR VOLTAGE AT THE REAR DEFROST, IF THE ELEMENTS ARE BROKEN IN THE WINDOW THERE IS A REPAIR KIT YOU CAN DYI. KINDA LIKE PAINTING A NEW ELEMENT ONTO TEH WINDOW WHERE THERE ARE GAPS

    HOW ABOUT THE SWITCH

    DAN








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      Rear window defroster 850 1997

      posted by  someone claiming to be JimP on  Sun Nov 3 09:25 CST 2002 [RELATED]

      Switch is OK and mirrors are heating. Where is the contact for the window element? Is it behind the roof pillars? How are they removed?

      Thanks for the suggestions thus far and for any further help.







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