Rear Window Defogger

[St Thicket]

The defogger is not working, and it has never done so as long as I've owned the car. There's evidence that there used to be toner film on the window before.

I've measured if there is a break before the power reaches the window, but it seems to be fine. I've measure the resistance of the whole window, and it is approximately 5 ohms in total... now the problem is to find the points where it's broken. When I try it out, it seems like every single wire is broken, but there might be one singe wire that works because there's conductance.

The question is... is it possible to retrofit a new defogger, or do I need to replace the whole window? New window seems expensive.

[shcm]

Yep, you could use resistance measurement.

The other way is that if each wire is complete it should act as a potential divider.

So, power the thing up and try each window wire in turn. If the wire is good the voltage between one end and the middle should be about half Battery voltage. If it is broken, it will be either 0V or Battery V.

To find the break, a recommend method is to put a piece of aluminium foil around one of the DVM probe ends and flatten a piece of foil out (will look a bit like a little flag (the foil) on the end of a flag pole (the probe)). With the other probe at one end of the wire, slide the flat bit of foil with the other probe along each suspected broken wire until the voltage changes from Battery to 0V or vice versa and you have found one break. Of course, you might have multiple breaks in each wire.

I know in your case, this should be relatively easy for you to understand.

It's been covered before that you can get silver loaded epoxy/paint:

http://uk.farnell.com/jsp/displayProduct.j...e-2072-00001000

to effect a repair. Masking off the window along the wire, will probably give a neat result. You probably have nothing to loose trying, although silver loaded epoxy/paint is never cheap.

There's going to be something like a 30A fuse for the rear window and mirrors combined, so I'd expect a lot less than 5 ohms.

[St Thicket]

So, power the thing up and try each window wire in turn. If the wire is good the voltage between one end and the middle should be about half battery voltage. If it is broken, it will be either 0V or battery V.

To find the break, a recommend method is to put a piece of aluminium foil around one of the DVM probe ends and flatten a piece of foil out (will look a bit like a little flag (the foil) on the end of a flag pole (the probe)). With the other probe at one end of the wire, slide the flat bit of foil with the other probe along each suspected broken wire until the voltage changes from battery to 0V or vice versa and you have found one break. Of course, you might have multiple breaks in each wire.

I know in your case, this should be relatively easy for you to understand.

Thanks for the advice! I Thought about measuring until the voltage change, but the tip about using the aluminium foil was quite smart! Trying to hit the wires with the thin probe tip sounded quite time consuming... :P

There's going to be something like a 30A fuse for the rear window and mirrors combined, so I'd expect a lot less than 5 ohms.

That's what I thought as well... I should expect about 0.5 ohms.

When I do a visual look of the defogger, it seems like someone have used a knife to remove the toner film... so I fear that it might be easiest to replace my window :(

[local hero]

Many years ago you used to be able to get a stick on rear screen heater, Don,t know if they are still available, and TBH they weren't the most stylish item but they did work TRY THIS.. https://www.europaspares.com/prod.asp?produ...&imgstate=0 Its a bit slow, but if you google rear screen heaters there are loads of products available for repairing + replacing your rear screen

[Hoovie]

I got my rear screen replaced under the insurance - cost £50 for the excess and that of course included a brand new heating element ;)

of course in my case it was due to a flying stone smashing through the glass from a silly workman.

[anchorman]

Yes all glass is insured and if you were silly enough to leave a ladder in the garage that could slip and crack it........

[St Thicket]

I thought about mentioning this in my previous post, but I didn't want to sound immoral and inspire to insurance fraud... but of course, these things COULD happen.

However, I prefer not to fill the boot with glass fragments.

EDIT:Just found out that the insurance cost for changing a window is £200... which is a bit more than expected.

[Davrav]

I thought about mentioning this in my previous post, but I didn't want to sound immoral and inspire to insurance fraud... but of course, these things COULD happen.

However, I prefer not to fill the boot with glass fragments.

Well if the ladder was inside the car and the door was shut against it..........................................

[anchorman]

The ladder in my garage would fall when the door was open. I really must move it!!!

[Hoovie]

I thought about mentioning this in my previous post, but I didn't want to sound immoral and inspire to insurance fraud... but of course, these things COULD happen.

However, I prefer not to fill the boot with glass fragments.

EDIT:Just found out that the insurance cost for changing a window is £200... which is a bit more than expected.

I found bits of glass in my boot months afterwards after having the rear window replaced (and the rear heated element still worked at the time it was broken by the careless workman (not me!) )

£200 excess for glass replacement?? you Norwegiens get stung for the glass as well as the beer in the glass. Ouch!

[Bodgit-fixit-run]

This may be an urban myth but I either heard or read somewhere that the original stick on heated screen heaters were in fact the precurser to the modern printed circuit board. Hows that for progess? Yep the pain is very expensive I bought some which worked really well on an old car. it cost about £7 for a tiny bottle.

[three5]

The defogger is not working, and it has never done so as long as I've owned the car. There's evidence that there used to be toner film on the window before.

I've measured if there is a break before the power reaches the window, but it seems to be fine. I've measure the resistance of the whole window, and it is approximately 5 ohms in total... now the problem is to find the points where it's broken. When I try it out, it seems like every single wire is broken, but there might be one singe wire that works because there's conductance.

The question is... is it possible to retrofit a new defogger, or do I need to replace the whole window? New window seems expensive.

Couple of (late) ( as usual ) ideas on this problem:

I used to have some narrow mettalic self adhesive tape that could be used to create a heated rear screen. I've just been and had a look in the garage and I guess that I threw away the residue of the last roll that I bought from a local auto-supplies outlet as part of a kit. It worked very well on a sucession of 2A Land Rovers except that the "path" was a bit short so the temperature got quite warm! The end connections to the tapes was made by overlaying the ends of the tapes with a "bus-bar" made from the sort of braid that you can remove from screened or co-ax cable, that too was held in place with a metallic adhesive tape. End connections to tha bus bars were made from crimped on lucar connections. The availability of specialist adhesive tapes has increased in recent years, so a google search might find a suitable one. Probably need to be 2.5 - 3.0mm wide and about 0.05mm thick aluminium if I remember correctly. The whole job was fairly neat and durable when finished

Never thought of using SCHM's method of finding the faults with aluminium foil, but the same sort of braid fastened on the end of the DVM probes might work quite well for that purpose as well.

[Uncle Bob]

Can i share my experience of HRW repairs.....no, ok i will anyway :P many years ago i had a Rover SD1 V8 and that had an element broken, so i used the liquid circuit board paint and put several coats in the area i could see the scratch, off i went to work next day 'put the heater rear window on to clear the condensation, 20 mins later there was an almighty bang and a blue flash , the rear screen had exploded :o it turned out this was due to a heat build up in the area i had repaired, so my advise would be don't go down the route but then again if you did ,you could claim a new rear screen with a clear conscience :)

[Davrav]

Can i share my experience of HRW repairs.....no, ok i will anyway :P many years ago i had a Rover SD1 V8 and that had an element broken, so i used the liquid circuit board paint and put several coats in the area i could see the scratch, off i went to work next day 'put the heater rear window on to clear the condensation, 20 mins later there was an almighty bang and a blue flash , the rear screen had exploded :o it turned out this was due to a heat build up in the area i had repaired, so my advise would be don't go down the route but then again if you did ,you could claim a new rear screen with a clear conscience :)

I think you might have overdone the conductive paint Bob!

I have used it to good effect, with no disatrous consequences, on two BMWs and they are well known for having delicate electrics.

[St Thicket]

Thanks for all the valuable advice!

I think I'll have a look for the tape first, since I think there might be several broken points on every path. If nothing is easily available, then I might go for the silver paint as schm recommended.