Troubleshooting rear window defroster defogger question
 

The rear window defrost doesn't work in my 240. I've got 12v to the wire under the C pillar trim, but none of the lines work. Am I correct in assuming that it's time for a new rear window?

Is the other side grounded?

Haven't even looked. I will though.

On mine I believe there to be 3 different elements in the glass. Mine used to all work, now only the lower 3rd of the defroster works. There is some delamination(sp) of the glass in the corners.

Safeco carries the rear glass w/heater, but is pricey.

On my 123 the Grid is external to the Rear Window Glass and on the interior of the Glass. While I can get current to the main copper areas what I found is that my entire grid has sort of a corroded cancer.
If you look in the pics you see the gird line with Copper Colored and Brown spots on it. The Brown spots represent a break in the circuit where it the grid has oxidized.

The ground on the passenger side is good. I have just over 11v to the connection point under the C pillar cover at the rear window. I get infinite ohms when I test resistance across the window at the two connection points. Is my rear window toast?

I have the same challenge...and am experimenting a bit...I just installed a kit from www.frostfighter.com. I they're the only source of aftermarket electric replacement defrosters I was able to come up with. I'm already troubleshooting it as all elements didn't work BUT that was my installation mistake-- I messed up making the connection to the bus bar. I can say it was very tedious to install...small hands would've been a benefit working in tight places.

Installing it I elected to scrape off all of the existing defroster wired with a single edge razor blade, clean the window with acetone and then proceeded to individually layover the new defroster wire in the same position the old one was so the window would look right. Like I say...tedious.

Doing it over I would likely look for a new rear window...if I'm successful in getting the thing working 100% I'll post a step by step. Just wanted to give you something to consider...

Have you tried to work at removing the oxidation - perhaps with a metal polish? - I imagine you would want to be careful about the application.

This is what mine looks like in the 240D, too. I have current all the way across the glass, but it must be low by the time it gets to the passenger side to effectively defrost.

I have about 3 wire grids working on the 240. plus the PO have a window sticker in the lower left corner covering some of the wires. removing it will just screw up rhe wire grid removing it.

so I`ll just find a good used on from PNP. hopfully a clean one will arrive.

that Frostfighter link looks good. would be easy to apply with the window removed. which I need to do anyway to replace the cracked 30yr old cracked and sun cooked gasket.

Charlie

I need to replace my window seal as well. So I am debating just replacing the window. I just hate to drop a bunch of cash on a new window and not have the problem fixed.

I just got a quote for new rear glass. $600!!:eek:. I'm waiting on quotes from a couple other places that are looking around for it. No one can find one.

How would one go about making sure the rear defrost is good in a piece of used glass?

Have you tried safelite? Their quote for my rear glass is $281 installed.

Apparently Safelite can't get the glass either. What the hell.

The oxidization is all the way through the metal in every one of those brown spots. The metal would have to be chemically turned back into Copper.

Hm, mine only the top third of the lines work... Maybe I'll get around to checking them someday...