Rear window defroster stopped working - PeachParts Mercedes-Benz Forum

pberku · #1 12-17-2003, 06:43 PM

My car is a '95 E300 Diesel (124 body).

The rear window electric defroster suddenly stopped functioning. The light on the defroster switch does not come on. I checked all the fuses and they are all OK. However, when I removed the defroster fuse and checked for voltage at the fuse box there was no voltage at the defroster fuse terminal. What do I check next?

I assume that there is a relay somewhere since the defroster works on a timer, but I have no idea where that relay is?

Any ideas,?

Thanks

Phil

Toblin · #2 12-17-2003, 07:54 PM

Swap out the fuse for another and retry. If it turns out you have a broken wire on the window they make a paint able electrically conductive fix-kit. But try switching the fuse first. A visually intact fuse could be a lying to you.

pberku · #3 12-17-2003, 08:39 PM

Unfortunately its not the fuse, as I am not measuring any voltage (with the ignition on) for this particular fuse socket at the fuse box.

By the way, my car has a circuitry that turns off the rear window defroster and/or the heated seats if the current draw on the battery is too high. This could happen when the glow plugs are on, but then the heated seats lights as well as the light on the defroster switch flash on and off until the high current draw is eliminated. (i.e.: when the glow plugs go off).

I don't think however that this circuitry is the problem since the light in the defroster switch does not even come on, and as I mentioned there is no voltage at the fuse box to the defroster fuse.

Any other ideas?

Thanks

Phil

rickjordan · #4 12-18-2003, 01:47 AM

Phil, I just repaired the rear defroster on my '87 TD (W124) and learned a few things. One the light in the defroster switch is a LED and is independant of the rear defroster. By that I mean, my rear window defroster was not working yet the light was on. My problem was a clean wire break towards the hatch. So the light in the switch is not indicating that the rear window defroster is working, just that you hit the switch. So with all that said, for your light not coming on, it could simply be the switch. Is this how you figured the rear window defroster wasn't working, or was it not clearing up?
At the moment I forget which fuse runs the rear defroster.

pberku · #5 12-18-2003, 10:03 AM

For some unknown reason, (which concerns me a bit) the light on the switch started working again and the defroster is now fine.

I am still not sure why I did not have any voltage at the defroster fuse (as measured with the fuse removed). I did not measure it again yet (3" of snow so far this morning) but I am assuming that the voltage is now also back.

I'll wait to further diagnose the problem if/when it happens again.

for now all is fine.

Thanks

Phil

84300DT · #6 12-18-2003, 06:44 PM

For some unknown reason, (which concerns me a bit) the light on the switch started working again and the defroster is now fine.

ahh, the old 'self healed' syndrome.. know it well here

when in doubt .. do nothing and be patient and sometimes things will work themselves out

richard28 · #7 12-29-2003, 01:19 PM

Rick, from where do you trace the wiring, & where & how did you find the break? My w124 defroster also doesn't work, & I suspect the wiring too. Thanks

rickjordan · #8 12-29-2003, 01:34 PM

Richard28, keep in mind have a wagon. I had the trim removed on the rear hatch and knew that all the wiring had to go through the rubber "elbows" at the hinge area. I removed the interior trim piece in the ceiling and found a junction point where about 14 wires were attached. This junction point was where the wire runs from the front of the car met up with the wiring going to the hatch. Using the wiring diagram from the service CD I found out what wire number was for the rear defogger. Using a meter I found out that I had voltage at the junction point but not from there to the defogger element. I also ohmed it out and I got an open between the junction point anf the defogger element, which of course meant a break. I removed the screw holding down thw wire and pulleed on it and there it was, a clean break.
I see that you have a sedan, so I would suspect that you may have a similar junction point but it would be mounted on the underside of "hat shelf" in your trunk.
The wiring diagrams don't really tell you where exactly the components are.
Ok, I just checked the wiring diagram for sedans/coupes, there is no junction point for these models. It is a straight shot from the relay to the rear heating element. The wire is black and is a 12 gauge wire.

richard28 · #9 12-29-2003, 01:47 PM

Thanks Rick. On 124 sedan, are you sure junction is under the shelf. I think someone told me it was in the rear roof sort of above where the outside shoulder of the passenger behind the driver would be? BTW, how do you remove the interior trim from the ceiling ? Thanks

rickjordan · #10 12-29-2003, 05:51 PM

As I mentioned, when I looked at the wiring diagram it shows that it is a straight shot from the relay. Only the wagons have this junction point. As far as how to remove the trim, I am not familar with the sedans. I mean I have riden in them, but didn't pay particular attention to the rear trim. When I get a chance I'll see if the service manual gives a description of the procedure.