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carazide
PostPosted: Sat Dec 09, 2017 9:08 pm 
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Hello guys!

"Winter is here, and it's cold!"

That being said, it would be wonderful to have a fully functioning rear window defroster/defogger (Whichever is right?).

Now, i tried to diagnose the problems as best as i could, but i have hit a wall.

The upper 5 wires/lines work perfectly, and melts any ice or snow that might be on the window, but below that, that's when it starts working, well, sometimes.

Initially i tried to measure the current going through the wires to see if there was any faults where they might be broken or otherwise, but i have the same, steady current going through all the wires on the entire window - same amount on the ones that work, as for the ones that don't. I have cleaned the windows thoroughly, to make sure no current takes any shortcuts or anything like that.

Now, the lower lines/wires well, they work sporadically. Some sections of them don't work at all, and then suddenly, in the middle of the window there seems to be a spot where they work, and it defrosts an area, only to stop further along.


Do anyone have any idea what's causing it to be like this, and what i can do to fix it? If you need pictures, i could be persuaded to upload some!

Thanks in advance
Jacob


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maZZda
PostPosted: Sat Dec 09, 2017 10:41 pm 
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Did you measured the lines that spread the electricity to all the litlle lines for breaks?
I have that problem with some lines don't working/heating.When a line do not heat/work it's just because there is no current throughout it.Check the 2 ends of each line for breaks from the main plus and minus vertical lines.They need some little microscopic break and will not function..
Easy repar is with copper spray.Just use wide paper tape arround and making thin line where the break is, spraying over it and it's done. ;)


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CSR
PostPosted: Sat Dec 16, 2017 12:44 am 
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mazzda that reall works?? I tought that once the lines where separeted (broke) there is no solution, only buy another Glass....


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Dark_Jon
PostPosted: Sat Dec 16, 2017 9:28 am 
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My Car: Mazda 323F ZXi

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You can buy silver paint for repairing circuits that can be used to fix this problem. Had the same issue on an old Jag and my dad (an electronics engineer) had some silver paint used for repairing circuit boards. Cleaned up both sides of the break in the rear demister line, tiny bit of paint, and it worked again.

This kind of stuff:

https://www.maplin.co.uk/p/electrically ... aint-n36ba

Even lists in the description 'repairing demisters on car rear windows...'

Jon


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maZZda
PostPosted: Sat Dec 16, 2017 4:09 pm 
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CSR wrote:
mazzda that reall works?? I tought that once the lines where separeted (broke) there is no solution, only buy another Glass....

Yep, it works.Done that on more than 10 different cars now..
There is a special laquer with aluminium particles in it wich is specially for that kind of breaks.. but it cost same as a copper spray (well here in BG) so for me copper spray is the choice..


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Steve Zodiac & Robbie
PostPosted: Sat Dec 16, 2017 5:05 pm 
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Can get the "paint" from auto shops too http://www.halfords.com/motoring/paints-body-repair/adhesives/granville-rear-heater-repair

The whole demister is one circuit so testing one line with a meter won't work, the other lines will carry the current so what I've done in the past is work out which ones are broken by either waiting till winter or spraying a fine water mist over the lines to see what will dry and what won't

I then usually wait until the summer as the light is the best and the window will be dry (no garage here!) and carefully examine the whole line which isn't working, with good light it usually shows up dodgy parts and as the paint is easily applied do anything which doesn't look right. Sometimes had to go back to it but eventually I got there.

Your problem with a patch and sometimes it works makes me think it's a tiny break which in certain temperatures will close up enough to then allow current. Occasionally when I've used the paint there has been a "hotspot" where the thicker line creates a hotter area so will demist faster, you're not describing that with the patches you describe?

It's a good indicator on how the car has been treated in the past with how many lines are broken, 99% of the time it's because owners aren't careful with closing hatches or loading the car in first place, the lines break when something hits them, either a closing hatch onto something or a load moving and hitting the window, I've got a mixed result with my cars, ,the Charade is 27 years old and all of them work no problem, my Saab is 25 and around only 3-4 work and the bottom line with the rear wiper section has been obliterated by a dealer sticker :roll: and everytime it gets cold I cant hardly see anything but when the summer is here I just think meh, I'll do it next week and of course before you know it it's the middle of winter :lol:


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maZZda
PostPosted: Sun Dec 17, 2017 10:49 pm 
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Steve Zodiac & Robbie wrote:
Can get the "paint" from auto shops too


You can do it on your own for less,less.. here is how..

https://www.youtube.com/watch?v=egMr9kk1uHk

Steve Zodiac & Robbie wrote:
The whole demister is one circuit so testing one line with a meter won't work, the other lines will carry the current so what I've done in the past is work out which ones are broken by either waiting till winter or spraying a fine water mist over the lines to see what will dry and what won't


If you measure resistance should give you exact same numbers for all the lines(thin lines) if there is a higher number there is the broken line as the electricity travels troughtout another line(the path is longer, hence the bigger resistance numbers) but that needs good multimeter.. :!:

The best way is with thermal camera..(wich my friend's phone has) :roll:


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pitrack_1
PostPosted: Mon Dec 18, 2017 4:15 pm 
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You can measure the resistance with a basic multimeter to determine where the break is. I haven't tried this, but the theory should work ;-)

0) Leave the rear demister OFF and disconnect the connectors to the rails (the thick vertical end bars that join the ends of the lines) just in case there's some weird sort of grounding.
1) Probe both rails to measure the resistance (ohms on the multimeter). This will give you a baseline reading.
2) Probe a 10 cm gap of a known good rail. This will give you a baseline reading for a connected 10cm section. I'll assume it will be different to the rail-rail reading. If not, try say 5cm or 20cm.
3) Now probe a 10cm (or selected size) gap (near the end) of a known broken rail. The value should match, or be close to the value of the 10cm gap of the good rail.
4) Move along the rail in the selected size. Each time the value should be near, or the same as, the 10cm gap on the good rail. When the value jumps suddenly:
4a) When there is a sudden jump to a finite value more than the value of the rail-rail reading (and certainly more than the selected gap reading), you have straddled the break point (or break points) in that selected gap. Note this assumes there are no further breakpoints outside that selected gap in that wire- in which case the resistance will go to infinity (see 4b)!
4b) If the resistance goes to infinity there are further break points outside the selected gap in that same wire as there is no conductive path either inside the selected gap or outside it that join the two probes. Continue the process to isolate other break points in the wire.
4c) You can reduce/increase the gap size to localise break points. For example, if you find a break point in the selected gap, halve the selected gap repeatedly until you isolate the break point to a small area.
5) Note the broken areas for repair.
6) repeat steps 3 -5 above for each broken wire.

You can do some basic diagnostic work with the voltmeter setting, but it requires the demister to be energised...and it's better (safer) working with it de-energised anyway. Nevertheless (and I haven't tried this either)...

1) Turn on the rear demister. Note you'll need the ignition on.
2) Using the voltmeter mode, measure the voltage across the rails (the thick vertical end bars joining the wires). It should be 12V (or close to whatever your battery is supplying)
3) You need to determine (and note) which side is +ve and which -ve (ground).
3a) If the meter reads +12V (or similar), the positive side is connected to the positive terminal of your multimeter.
3b) If the meter reads -12V (or similar), the positive side is connected to the negaive terminal of your multimeter. You can swap probe sides to confirm this, you should get the result from 3a) in this case.
4) Now probe between the +ve rail side and a spot very close to the +ve side along a known broken wire. The reading should be zero (or very close).
5) Maintaining the probe point on the +ve rail size, progressively probe points further along the known broken wire. The voltage should remain at zero until you jump a break point.
5a) If the voltage goes to 12V, you've straddled a single break point. Progressively move the probe point back until you isolate the break spot.
5b) If the voltage goes unstable but small (drifting, close but not maitaining a steady 0V) then you have more than one break point. You can continue along the wire until the voltage goes to 12V again in which case you 've straddled all the break points in that wire. You'll need to go to the resistance method above to isolate the multiple break points.
6) Repeat steps 4-5 for each broken wire.

Hope this helps,

Patrick


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carazide
PostPosted: Sun Mar 25, 2018 3:38 pm 
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Hey, thanks you guys, and especially you Patrick for this nice little guide!

I ran in to bigger troubles (inner CV joints busted, and no spare parts to be found anywhere!) So i put this on hold for a while.

But i'm definitely going to try this, and get back to you and let you know how it went! :)


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pitrack_1
PostPosted: Sun Mar 25, 2018 4:56 pm 
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Hi carazide,

glad the little guide is of help... I just hope my theories are right.

And yes the rear demister won't stop the car, broken CV joints of course will.

In the meantime, something like RainX Anti-fog should do the trick, but you may need to do all the interior windows, I've found that the condensation moves around to find the window that hasn't been antifogged and you don't want that to be the windscreen! If you need a 'sacrificial' condensation window, the rear pax one behind you I find to be the best as you can't see it.

Patrick


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