Rear screen demister not working

[matthewb]

Hi chaps

Stuck on the M25 last Thursday (anyone else?) in stationary traffic, I decided to turn off the engine and lights. I soon got cold and the windows misted-up, so I turned the ignition to activate electrics, pulled the rear demister knob, it lit up, I let go of the knob, the light went out, the rear screen didn't clear.

A couple of years ago, I had some work done to fix rust below the rear screen. The rear screen had to be removed to fix the problem. I have noticed a thin cable running behind the speakers that hadn't been properly dressed but haven't really worried about it.

I very rarely use the rear screen demister - this was the first time since having the repair done - so I don't know when the problem started but obviously I suspect the rust-repair job.

The rear wiper works.

Any ideas? Where is the rear screen electical connection? Is it accessible to a layman? Is it a big / difficult job to track-down the problem?

Thanks all in advance.

 

[Mark Elder]

Hi Matthew,
Sounds like more of a switch (or relay) problem because I'd have expected the light to stay on for the 5 mins (or whatever the timeout is) even if the line to the heater element was disconnected. That switch also runs the heaters in the side mirrors and the heaters in the windscreen washer nozzles. I'd start by doing some relay swapping if anyone knows which relay it is for this circuit??

 

[clyde]

Could be that they didn't re-connect the demister wires when putting the screen back in or they've broken. The wires are at the base of the screen in the middle and are accessed by removing the rear parcel shelf, which is easy enough - only about half a dozen screws, plus the rear belt lower mounts. I believe the earlier cars (pre 95) had the wires at the sides of the screen and can be seen by peeling back the window rubber.

The three consul switches have a natty means of turning off the built in light by unsrewing them about a quarter of a turn, so make sure it is tight before assuming the switch isn't working.

As Mark suggests I would look at fuses/relays first - the inside of the fuse box lid will tell you which they are as they're all listed and numbered. Next I would test the switch and its feed with a multimeter before taking the parcel shelf out to check connections.

 

[Porker993]

Ditto. Suspect fuse/relay.

 

[Simon P]

I have just had same problem of rear demister not working. Mine has power to the rear window but connection to screen has gone. According to my Indie, this is really common, but the really bad news is that the damaged connection to the screen can then spark, sometimes causing the rear screen to break! And they cant fix it unless screen is changed. Oh joy!!
Simon

 

[matthewb]

Thanks for the responses everyone, and apologies for my tardy response.

It seems to have started working again of its own accord (or perhaps it was never broken and it was something I was doing wrong) - waiting for a damp day to test out the demister properly.

Cheers
Matthew