Defrost Lines Diagnosis/Repair

[Fitz98]

Rear window was fogged up yesterday. Getting everything ready for a tint job.
Tested rear defrost and only 50% of the feature is working.
I have one contact on one side that needs to be re-attached, so this result in the picture is after me manually holding the contact in place. The one on the other side is still connected.
I have tested continuity from the main vertical strip across all lines and they all have continuity on both sides.
I have tested voltage to ground and all the horizontal lines have the same voltage to body ground.
I can feel some heat on the main side strips down to the area on the bottom where it is not working and then the strip is cool.
Nothing defogs just by having the one good side connected, but there is good voltage with just the one good side connected.

What else can I test for? I would like to have these working before tinting, but if not, it won't be the end of the world, but it does help clear rear window for better visibility on humid rainy days.

 

[97prizm]

It sounds like a break in one or several of the defroster lines. I saw a diy defroster kit at Walmart a while back. Not sure how easy to use or its effectiveness.

 

[Fitz98]

It sounds like a break in one or several of the defroster lines. I saw a diy defroster kit at Walmart a while back. Not sure how easy to use or its effectiveness.

I would not be surprised if there was a break with the removal of the old tint and scraping and cleaning process.
Wouldn't explain why I have voltage and continuity on all lines though, unless my testing procedure is not correct.

 

[ctechbob]

It would be possible to show continuity and voltage but not be able to pass enough current to heat the line.

Think of it as having a multi-megohm resistor in series in your circuit. You'll show continuity and be able to measure voltage across it, but precious little current will flow through it.

Sometimes you'll actually be able to see where the break is on a foggy window. It will heat the area in just a little spot around the break and clear the fog, but not the whole line. But if the break is big/wide enough you won't see it.

Easiest way then is to have the car in bright sunlight and look for variances in the lines. Breaks will be lighter than solid lines.

I will caution you though on using line repair products. Usually when you tint over them, the tint won't lay down properly around them so you'll end up with a little bubble in that area. So if you use a repair, try and apply it as thin as possible to get the job done.

 

[Craig in Canada]

I would expect in most designs - the "continuity" you're measuring isn't strictly through the path you want the electricity to take between the probes. It's any path between the probes. Including all of the other lines that are working. If your window is wire terminals on each side with a large vertical coated strip, then each line running between the positive and negative coated strips, you only need to have any one line working and you'll get "continuity".

I'd probably get in nice and close or with a magnifying glass and good lighting and look for physical damage on the inoperative lines, then see if you can repair it yourself.

 

[Thermo1223]

Ya they make a metallic paint of sorts that you can bridge the gap with on broken lines.

 

[Fitz98]

I think I found the source of the problem.
When I was manually making my connection to defog the window, I was lining up the solder on the pads with the matching locations on the defrost main strip.
I have continuity everywhere, except where the #1 old pad location is on the side strip. When I put my one of my leads at that #1 location, I lose continuity to all the strips.
I will need to retry with the pads contacting the intact parts of the main strip instead of the old location where the power connector was ripped away from the main contact strip, pulling the conductive material with it.
It would probably be good to somehow repair that torn area as well...looks like a pretty large piece of conductive material missing now.

I wonder if this would help repair the conductivity of that area?
Defrost Contact Repair Material

 

[SHOZ]

I used some of that to glue one of my leads back on. been OK for a few years.