Rear Window Demister Fault? - Alfa Romeo Forum
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(Post Link) post #1 of 15 Old 19-11-13 Thread Starter
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Rear Window Demister Fault?

Hi

I noticed this morning that when I pressed the demister button on the dash the button light came on as normal but the window did not demist/thaw.

Any ideas as to what the fault is? Could it be a fuse?

Many thanks

GJP
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It is annoying when one day the rear window defroster (demister) works and the next not.

Try checking the easy items first. Take a look at the fuse, the location of which is likely shown in the vehicles manual. Check to see if the light comes on when the defroster switch is pushed. When you push the defroster switch you are likely to hear a click as the relay makes.

Assuming these items check out, next take a look at the tabs on the defroster. These tabs are normally located along sides of the defroster and connect the unit to the vehicle’s defrost circuit. A separated tab will stop your defroster cold. If you find a loose or hanging tab use the Frost Fighter Defroster Tab Bonding Kit to reattach the tab.


If the tabs check out as attached to the defroster then check to see if you have power at the defroster tabs. A multi-meter or 12 volt test lamp is handy here. Turn on the defroster and place the probes on each tab. You should see 12-13 volts across the tabs.

If you have power to the tabs it means that the defroster circuit is likely functioning and the fault is in the defroster. We have a good trouble shooting guide online here



Let us know what you find,

DOC

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As the light is coming on shouldn't be a fuse possible. The wiring going through the loom at the tail gate is a common fault for breaking.
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It's a fault in the loom. I had mine replaced under warranty last year.
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I thought mine had stopped working, turned out there was a layer of dirt/oil on the inside that when in darker conditions and at night with the car behinds light shining it that gave it the impression of having condensation/frost on it that would never go away
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Thanks all. Getting it checked out under warranty on Fri so will keep you posted.
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I know this was 4 years ago now, but did you find out what the cause was to your demister problem?

I am now having the same problem, checked the fuse and its fine.
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Most likely the wiring loom to the rear tailgate. These cables get stressed when the boot opens then break internally.
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I think the wiring loom stress is manifesting itself in a failed reverse light on my car
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My rear demister has stopped working and I'm assuming a break in the cable loom.

Question - Will a none working rear demister = an MOT fail ??
I've googled and some people say yes and some no. I can't imagine its something they would check. The dash light comes on so it 'looks' like its working.
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Quote:
Originally Posted by philbean View Post
My rear demister has stopped working and I'm assuming a break in the cable loom.

Question - Will a none working rear demister = an MOT fail ??
I've googled and some people say yes and some no. I can't imagine its something they would check. The dash light comes on so it 'looks' like its working.
Theyd have to be able to test for it, doubt they give off enough heat to be checked with any basic thermal equipment so unless there was actual condensation on the rear at the time of testing i'd be very surprised.
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Alfa introduced a more study loom some years ago for the tailgate. As far as I know Alfa covered the change if the car is still under warranty.
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Could also be a break in the track on the window itself, easy to visually check too.
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I am going to go with the wiring loom.

There is about 30 amps flowing through the wires for the window, and if there is any fatigue in them they will soon burn out and give an open circuit.

If you are handly with a soldering iron and have some heatshrink sleeve it should be easy enough to find the wire responsible and splice a new section in without having to buy the repair kit for about 60.
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Quote:
Originally Posted by symon View Post
I am going to go with the wiring loom.

There is about 30 amps flowing through the wires for the window, and if there is any fatigue in them they will soon burn out and give an open circuit.

If you are handly with a soldering iron and have some heatshrink sleeve it should be easy enough to find the wire responsible and splice a new section in without having to buy the repair kit for about 60.
Would the broken boot wire not give the same open circuit though?
For some reason the bottom two lines of mine do nothing, there is discolouration but I've not looked properly yet..
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