Rear defogger

Heating, Cooling & AC

  1. Bruce311

    Bruce311 New Member

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    I'm New to the c body formals. I just got a 77 nub and as the days go by, I find little things wrong with it. Not too much but still trying to figure out everything. I tried searching, but couldn't find anything. When I flip the rear defrost switch, the orange light comes on but goes off right away. Could it just be a short, or bad switch??
     
  2. traintech55

    traintech55 Senior Member FCBO Gold Member

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    No. First I take it you have a heated rear glass, and not the blower type? The blower type did not have a light by the switch to show it was on. Sounds like you have a bad relay in the system, BUT be very careful to disconnect the power to the back glass when testing. If the glass overheats it will explode and good luck trying to find a new one.
     
  3. Davea Lux

    Davea Lux Senior Member

    My Photo Garage
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    If this is a heated rear glass, the switch might turn off if there is no continuity to the heater. Check it for cracks or gaps in the heating film. The switch will also turn off on some models if there is insufficient voltage to the switch. The switch might also be bad. As mentioned above there could also be a bad relay that is preventing a completed circuit to the heater. Did you test the heater with the motor running, if you turned on the heater with just the key on, you might not be getting enough voltage to operate.

    Dave
     
  4. Bruce311

    Bruce311 New Member

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    It snowed over the weekend and was a perfect time to check how the heater and defroster worked, so I let car run for about 25 minutes. That' when I found out defroster wasn't working. I' gonna take a look at it on Wednesday an see what I can find. Thanks guys for the suggestions so far
     
  5. akiran

    akiran New Member

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    Inside the switch there is contact breaker. Clean oxidated points with smooth abrasive paper. Take care not scratch the points or bend the lobes. This switch was develloped to the analog world. It contains bi-metal lobes that work as a timer. When they are warmed up, they cut off the rear window heater.