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I have 2012 Volvo S40. At some point, something has scrapped against the window and broken a few of the grid lines. The result is that part of the defroster grid does not work. Most of the window does defrost, it's just around the lines which contain a broken connection that it doesn't.

How can I fix this? I've seen some conductive paint/glue products to repair the individual lines, but I'm a little sceptical from the reviews of such products. If this is the best solution, I'd appreciate any suggestions of ones to avoid and try.

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    Welcome to Motor Vehicle Maintenance & Repair!
    – Pᴀᴜʟsᴛᴇʀ2 ♦
    Commented Sep 10, 2018 at 17:24
  • If you can spring for it install a new back window, wherever you repair it it will no longer heat in the repair areas, it does repair the circuit but the repair product does not heat up like the factory lines.
    – Moab
    Commented Sep 12, 2018 at 22:36
  • @Moab is that because the repair product is inferior? Or because it's difficult to 'paint' on the product to the same width as the original lines? My thinking is that the bigger the line, the less resitance, thus less heat generated.
    – DJH
    Commented Sep 13, 2018 at 8:45
  • It is because it is a repair only to make electrical connection again, the original grid is resistor material which gets hot, the repair will not.
    – Moab
    Commented Sep 13, 2018 at 14:18

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I did this once, it depends on how thick and wide the original lines are.

I cut back each side to well-stuck lines (does not work trying to join to loose lines), then masked the section that needed replacing, the idea is to get the masked gap to match - if it goes thicker it shows up...

Then I used 3 or 4 coats to build up the section. Whatever you do don’t switch the power on until it has dried thoroughly.

The product I used had a silver content but can’t remember any details...

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    The key is care and accuracy in preparing the window and applying the product will lead to the best results. If your window is filthy, or has tint on it, or there are loose sections of grid you are likely to get a sub-optimal result.
    – Tim Nevins
    Commented Sep 11, 2018 at 17:34
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In addition to Solar Mike's answer, I'd suggest the Permatex Complete Rear Window Defogger Repair Kit. It has worked well for me in the past.

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