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300CD Rear Window Defroster

1989 Views 7 Replies 6 Participants Last post by  KCM
In my '83 CD, the rear defroster does not turn on. I already replaced the relay with a used (but untested) one, but that didn't seem to fix the problem. The relay I replaced it with could be bad as well, but I hope not since they are expensive new and hard to find.

I don't think it is the switch only because the light comes on when the switch is pushed on, but I can't say for sure. (In the meantime, I've ordered another switch.)

Does anyone know how the rear defroster is setup in this car? I know the blower vents are back there behind the dash, but I don't know if they have a separate blower motor, if they are tied into the main system, or what. Id' like to test the blower motor to see if it is getting power, but I don't know where to find it.

Any information would be a huge help.
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1984 300CD, 2015 Sprinter 3500, Coach House Platinum II
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AFAIK the rear defroster is built into the glass. You have to get the correct angle to see the fine filaments. Additionally they run vertically on the coupes, as opposed to the sedans which run horizontal. I've never heard of an optional rear defroster blower on them before.
 

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Discussion Starter · #3 ·
AFAIK the rear defroster is built into the glass. You have to get the correct angle to see the fine filaments. Additionally they run vertically on the coupes, as opposed to the sedans which run horizontal. I've never heard of an optional rear defroster blower on them before.
Really? Hmm. That's interesting. I always thought there was a blower motor back there since there is a gap (that look like a vent of some sort) between the rear deck and the rear window and since those lines are so incredibly inconspicuous. They are definitely next-to-invisible, but I know what vertical lines you speak of. I always thought they were part of the safety-glass. :eek:

So the space between my rear deck and rear window then... that must be just vents for the speakers or just a useless hole, huh.

In any event, where is a good place to hook up a voltmeter to see if there is any power hitting that window?

Thanks.
 

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1979 280CE
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that just the useless gap.

Check the fuse, I had the same problem, the switch light came on but the window never defrosted. I replaced the fuse even though it looked OK and the defroster worked.
 

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Discussion Starter · #6 · (Edited)
that just the useless gap.

Check the fuse, I had the same problem, the switch light came on but the window never defrosted. I replaced the fuse even though it looked OK and the defroster worked.
My fuses are all good, but I'll do this for good measure. Thanks.

Still, It'd be good to know where I can test to see if power is hitting those filaments. I don't want to have to wait until my window fogs up to test the darn thing. Thanks!
 

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My fuses are all good, but I'll do this for good measure. Thanks.

Still, I'd be good to know where I can test to see if power is hitting those filaments. I don't want to have to wait until my window fogs up to test the darn thing. Thanks!
I'm fairly certain the air gap you see between the package shelf and window is a vent between the trunk and passenger cabin so that air can pass between the two when closing the doors or the trunk lid. If the car is too air tight, the doors can be hard to shut.

As for the rear defroster grid connections, they are located behind the rear quarter interior trim panels, next to the rear glass. There is one on each side, and I think the left side is the hot wire (the other side is ground). Don't know if you can get a probe in there without removing the trim panel. If you remove the trim panel, best to get instructions as I believe there are some plastic tabs that can get broke if done wrong.

If you do get it working, don't be surprised if not all the grid works. Seems that a common problem with the coupe defrosters is that the connections get bad at the ends (top and bottom) and you will have dead zones.
 
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