924Board.org

[flames]

I cant get either my front or rear window to demist. The rear one has 12V power to one side, and the other is earthing well, so any ideas?
Also the front demister seems to do very very little, after about a hour of driving about 1/4 of the windscreen may be demisted, but only on a good day.
Any ideas?
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'78 924
Carrera? Body Kit
Bright Yellow

[RC]

1. Wind down the window about 1-2 cm.

2. Measure resistance/continuity of rear window element, sounds like it has corroded open circuit (at least on some sections).

3. Check under dash for disconnected/missing ducting and operation of flap and cable.

Roger

[flames]

At the moment I am winding the window down to drive, but it is cold .
I did check the resistance across the rear window, can't remember the value, but it was connected, Also checked there was curretn flow, which there was.
How do the flaps on the 924 heater work? I have found that one of the sliding controls opens and closes the feet flap, does the other one just open and close the face one? And demisters are always open?
Thanks
Beau Logue
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'78 924
Carrera? Body Kit
Bright Yellow

[Lizard]

I am sorry you dont know what cold is living in AU, come and spend a winter in saskatoon Canada one winter, then you can talk about that. lol

you should verify that your blower motor is working properly, you have a thermistat installed, and the heater valve is good.
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3 928s,

[RC]

Flames wrote:

[Smoothie]

Check for frayed wires and clean all connections. I found my 12v+ supply at the rear defroster (a black heavy gauge wire that runs from the body and connects to the left hatch strut) frayed, with over half of the strands broken. When they're like that, you'll still get a 12V reading, but they won't pass enough amperage to defrost the window. The same can happen at any connection - you may get a 12V reading, but not enough current passes through to sufficiently power the component. It can also happen at switches - I recently sped-up my power windows by cleaning the switches. Start by checking/cleaning wiring and connections back at the hatch, then check the connections at the back of the fuse-relay panel for burnt/oxidized pins. The ground path for the rear defroster is through the right-side hatch strut - through the mounting, not through that small wire at the body end of the strut (that small wire is the ground for the luggage area light switch which is also built into the strut).
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"..it's made in Germany. You know the Germans always make good stuff."


'82 924T, US version, dark green metallic, 5 speed Audi 016G gearbox

[flames]

ok, on the rear window, what sort of amps shoul it be drawing?
I will stick my head up there tonight and look for blockages in the front.
_________________
'78 924
Carrera? Body Kit
Bright Yellow

[RC]

Mine is not connected so cant measure it. Fuse is rated at 16A so max draw would be around 10-12A.

The actual measured resistance is 2.5 ohms which will draw around 5A. Mine may be a little sus on some "lines" so take that as minimum acceptable value.

Using a DMM to measure resistance, first short the test probes to measure lead resistance then deduct this value from your reading.

Checking actual voltage across the element while energised will give an indication of system voltage drop. Considering 4.0mm2 cable any more than say 2V will be poor connectors, bad earth, etc.

Roger

[Mike924]

My front window was like yours; only a foot-wide band in the middle would demist.

The problem was the flap at the bottom of the heater/blower; the one which sends air to the footwell or upstairs. I wasn't closing the footwell vent properly, so with a bit of judicious tweaking, I bent the level rod (at the flap end) so that it closed better (still not perfect, though).

This sent a lot more air to the windscreen: it now clears about three quarters of the area.

The through-ventilation in these cars is not at all good. It's a bit too clever for itself. Air is supposed to be drawn through vents just below the rear hatch, forward through the doors ( ) and exit through the front door jamb. I think this really only works at speeds above about 45 mph. At lower speeds it's useless, causing the interior to mist up at the slightest excuse!
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1985 Porsche 924 'Lux', Kalahari Beige (my ex)
1993 Porsche 968 Coupe, Midnight Blue, 6 spd

'There is no substitute for a little grease under your fingernails.' - Chrenan, 924board.org

[flames]

interesting, so the big holes in door trims is not going to be helping things at all. will try sealing them up. Might stop the water coming in too
_________________
'78 924
Carrera? Body Kit
Bright Yellow