1993 Rear Window Defroster Not Functioning...

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Jun 24, 2006 | 02:50 PM

cousinit99

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From: Somewhere, Delirious

1993 Rear Window Defroster Not Functioning...

I have a 1993 LT1.

Basically, the rear window defroster doesn't work.

When I press the corresponding button on the heating and air conditioning panel, I'll hear something *click* inside the passenger-side knee bolster. The rear defroster light on the panel stays lit when I press its button, but nothing happens after I hear that clicking sound. After I press the button, the rear window remains frosty indefinitely and the heating coils on the window don't feel even slightly warm...

I've made sure that the electrical connectors attached to the window's two pneumatic lifts are clean and secure. I've also done a visual check of every fuse on the fuse panel and all are good.

Can anyone help me fix this? Also, what the heck is that clicking sound I'm hearing?

Thanks.

Jun 24, 2006 | 03:04 PM

MikeC4

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From: Austin Texas

disconnect the connectors and use a digital voltmeter to check for continuity between the left and right connector. This will tell you if there is a break in the window mesh zigzag(or whatever they call it?). It sounds like you have a break somewhere within the defroster chain.....The clicking...I have no idea...could be defective defroster relay....

Jun 24, 2006 | 04:27 PM

cousinit99

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From: Somewhere, Delirious

The continuity checks out. I just checked with my multimeter.

Thanks for your response, though. Any and all input is appreciated.

Jun 24, 2006 | 04:43 PM

MikeC4

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From: Austin Texas

Quote:

Originally Posted by cousinit99

The continuity checks out. I just checked with my multimeter.

Thanks for your response, though. Any and all input is appreciated.

I assume your multimeter also has DC current measuring capability. Disconnect the right and left connectors on rear window. Put one of the meters leads on left connector and the other lead on the right connector. Set the meter DC current range to highest setting. Now you can measure the series current that is supposed to go through the mesh. Turn your defroster on and off and see if the meter reacts. If it doesn't, most likely your defrost relay in dash is toast. I also am assuming you checked all applicable fuses.....

BTW, I love that Ruby Red...is that original paint...has a great shine to it!!!!!

Jun 24, 2006 | 05:36 PM

cousinit99

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From: Somewhere, Delirious

Alright, just checked that. The current doesn't change when I "turn on" the defroster. The relay is probably to blame, I think. Thanks for your help.

Original paint, why yes it is.

Thanks. She's my 40th.

Jun 24, 2006 | 06:07 PM

MikeC4

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From: Austin Texas

Quote:

Originally Posted by cousinit99

Alright, just checked that. The current doesn't change when I "turn on" the defroster. The relay is probably to blame, I think. Thanks for your help.

Original paint, why yes it is.

Thanks. She's my 40th.

Sweet car...that was my first choice color, but I wanted a '95 or '96, so settled for Polo Green. I sold it awhile back for the C5 you see in my avatar. I think I am going to get another C4 though, 'cuz I really miss it!

Also, on your rear defrost, I think your on/off switch is fine(you said it lights up which is good). The component I think may be at fault is the timer circuit switch. This is an electronic circuit that automatically turns off the defroster after about 10 minutes. This timer circuit also has a another relay associated with it, that feeds the 12V source to the window mesh. I don't think I was too clear on this. The actual heat that is generated is due to the large amount of current being pushed through the low resistive mesh, which should be approximately 5 ohms.

Also check that your grounds are solid. A bad ground will also kill the operation of defroster, as the current will have nowhere to flow. If you have service manual, you should be able to locate the associated grounds for this circuit.

Good luck.......

Last edited by MikeC4; Jun 24, 2006 at 06:15 PM.

Jun 24, 2006 | 08:31 PM

cousinit99

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From: Somewhere, Delirious

Thanks Mike. I'll give these items a real close look.

Gracci. Yours looks pretty sleek as well.

Mine was a steal when I bought her. The lot she was sitting on was full of exotics: Ferrari's, Lamborghini's, Aston Martin's, etc. The dealer was quite eager to help me roll her off the lot.

She came down with Optisparkitis (which the water pump was leaking on, by the way), like every 1993 that's spent its lifetime outside New Mexico has, I'm sure. Personally, I called it a Sh!ttyspark, or a TakesonwaterlikealeakyshipSpark. Anyway, I gave her a new water pump and a Dynaspark about a year ago, and she's been purring ever since. I'm about to replace the stock cats with Magnaflows and the exhaust system with a Billy & Boat. She'll like that a lot, I think.