Rear Defroster help

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Rear Defroster help

Postby TommyG » 17 Nov 2004, 21:50

Hello,

I've sort of inherited the task of maintaining my girlfriends 86 Chevette. Lots of various problems, but the most pertinent one now is the rear defroster not working.

My manual makes no mention of a rear defroster at all, and there is no on/off defroster switch that I see, and no fuses are marked for rear defogger.

Any help please??

Thanks!

Tom
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Rear Defroster help

Postby Neilyman » 17 Nov 2004, 22:41

The switch should be on the right of the ashtray, under the radio.
If you have no switch, should the car have a rear demister?
A plain rear screen could have been replaced at some time with a heated one due to breakage etc.
Do you have any wires connected to the metal tabs that are approx 1/2 way down the window at each side?
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Rear Defroster help

Postby Doive » 18 Nov 2004, 01:26

I'm guessing by the fact its an 86 Chevette that this is an american car? Its probably as Neily says, a heated screen was used to replace a plain one at some stage - good for you though!

All you need to do is rig up a live feed to one side, neutral to the other and you have a heated rear window. Remember to either use a fairly chunky switch or else a small relay as a heated window can draw up to 15 amps, and make sure its fused! British Chevettes have a fused supply going straight through the switch down to the back window. Mine is working a lot better this year than I remember it doing last year!
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Rear Defroster help

Postby TommyG » 19 Nov 2004, 00:31

There doesn't seem to be any sort of switch that I can see. I'm guessing it is a heated window that is supposed to be permanently on? There are two screws in the rear window and the wire comes out of the rear driver side where it attaches to the window.

It looks like a piece of the rear driver side bracket was broken and I'm not sure if it was reattached properly.

It is actually a Canadian Pontiac Acadian, which seems to be pretty much just a Chevette with a Pontiac name tag on it.

Thanks for the help.
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Rear Defroster help

Postby Doive » 19 Nov 2004, 00:47

Seems very unlikely to me that a heated rear window would be permanently on - I've never heard of such a thing, especially as the drain on the electrics would really nail your fuel economy!

If there are wires emerging from the pillars as you say, then one possibility is to trace the wire back to the front of the loom. It could involve a little removal of stuff, but there will probably be a point where all the wires for the rear of the car split from the front harness, stuff like tail lights, rear wiper etc. This could then be traced through the front harness to see if it runs to the fuse box, or if it simply terminates behind the dash for some reason?

Other possibility is to get yourself a wiring diagram to trace the wiring, but once you have the wire colour it *should* just be a matter of following it to the fusebox, then to the switch (or where the switch should be anyway!). The good news is that the wire you are looking for is already in the car and all you will have to do is feed that a positive supply if its found curled up behind the dash. Hope this helps a bit?!
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Rear Defroster help

Postby Crum B » 20 Nov 2004, 03:46

If there are wires to the rear window than theres got to be a swithch and if you want to test the wires get a cheap test light and ground it on something and touch the test light on the main power wire if it lights up there should be power to it.
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Postby Chevette Girl » 22 Jul 2005, 03:56

If I recall correctly, the wires on the Acadian (yes, it IS just a Chevette with Pontiac markings, they are completely and totally interchangeable) rear defog are at the top corners.... see if the wires are connected to anything... I actually drove one for a while that had the wires but the hatch from my old Vette was in better shape so I kept it... You'd think a car build for Canada would have the rear defog as a stock item, but this one had the sunroof instead, go figure.

If it was a stock installation, the switch should be to the left of the fan control on the console, has a little indicator light and everything. If not, it's anyone's guess...

It wouldn't be always on, in fact the 82 model stays on for about ten minutes or so and then the switch goes "POING!" and shuts off... like a toaster, only quieter (... and no toast)... it also shuts off automatically when you shut off the engine.
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