cleaning the window switch restored rear window - PeachParts Mercedes-Benz Forum

scottmcphee · #1 05-19-2016, 03:32 PM

Window rolled down 2 inches, and that was it.. finished the trip with a lot of wind noise. It had been getting intermittent before but now, nothing from either the central switch or door switch. No motor noise, nothing.

Research here suggested frayed wires at B pillar. So I stripped the pillar and door card off, only to find wires in perfect shape everywhere.

So I disassembled the door window switch and cleaned all its little internal parts and external contacts properly with light sanding of charred carbon (arc) residue, tarnish on silver parts, etc.. sprayed with contact cleaner w/PPT additive, and put it all back together and ... fixed!

I should have done this first. Because a few weeks ago, I had finally lost some directional controls of power driver seat, restored by overhauling the internals of the power seat switch similarly ... and restored all function of power seat.

It is a whole lot easier to pop the switch out and try this first, before taking pillar trim and door card off... just a tip.

How many cars list a routine maintenance item "clean the insides of switches" every 30 years ?!?
The fact that you CAN take switches apart and service the insides.. is unheard of nowadays.

ngarover · #2 05-19-2016, 03:48 PM

Mine has a bad/broken regulator. Been in there and it's a pretty week design, but doing the same as you describe. I had to start taping the window up to keep it from falling down 2 inches till I replace it.

Diesel911 · #3 05-19-2016, 03:50 PM

My experience has been that the contact points inside of the window switches needed to be scraped with a small Pocket Knife.

Others have claimed contact cleaner and or a Pencil Erasure did the job???

zu! · #4 05-19-2016, 04:43 PM

My drivers window stopped working once and I eventually had to remove it completely. Whilst it was out, I was pleasantly surprised to find that the entire motor is basically servicable. So I took it apart, cleaned it, greased it and put it back. It works perfectly now.

The only window not working is the passenger side rear. But it doesn't work either with the switches in front or in the door itself. What are the chances of the switches being the culplrit?

BTW, I cleaned my W123 switches too when I got them. NONE of the windows worked when I got them. I took apart the entire switches, cleaned them, and until the day it drove off to another owner, EVERY SINGLE ONE worked.

scottmcphee · #5 05-23-2016, 09:38 AM

Quote:

Originally Posted by zu!

The only window not working is the passenger side rear. But it doesn't work either with the switches in front or in the door itself. What are the chances of the switches being the culplrit?

Odds are good the window control switch on the rear door needs attention. The center console switches for window control rely on good contact in the door switches themselves because power is routed through them while resting in their neutral position in order for central switches to have an effect driving the window motor.

If you disconnect / unplug the window switch in the door, the center console switch cannot drive the window up or down. That's just how things are wired.

Trivia: anybody know what will happen (without trying first) if the driver and passenger have a tug-o-war over the passenger's window by using switches in opposite directions? Keep in mind this is an old German car.

Is it:

A) the driver command always wins and overrides the passenger every time
B) the passenger overrules the driver's command every time
C) the driver command causes the passenger command to pause (halt) the window, then the first to let go is the loser, whoever holds longer eventually wins the window going in their direction
D) if the driver started the action the passenger's attempt is thwarted and driver's chosen direction keeps on truckin' and vise versa for the passenger if they started first
E) so long as either switch is in the down position the window keeps rolling down
F) sparks fly or a fuse blows if you're lucky, you just put 25Amps through two switches and created a dead short
G) the motor conjigulates as it tries to satisfy both commands simultaneously, and depending on the state of lube of the window regulator the window may slowly creep up, or down at a fraction of the normal speed
H) all doors unlock if they were locked, but the trunk and fuel door remain locked, and interior lighting goes on

jay_bob · #6 05-23-2016, 10:01 AM

Please don't abrade electrical contacts to clean them!!!

The contacts in these old models were built nice and stout, with a solid copper core with silver plating. However if you scrape the plating off, it will work great for a while, but then as the copper oxidizes, the contact resistance goes way up. This gets the contact overheated, and then it fails permanently.

Please, instead of abrasion, try Tarn-x on a q-tip. If you can't find it, use silver polish and carefully flush out the residue.

It is a testament to the design of these older models that you can actually take a switch apart and maintain it. The seat and window motors draw around a dozen amps or so and the switch had to be stout to handle the load.

On the newer models, where you are switching a low level (milliamperes) signal to a digital module, the contacts will last forever, and it is normally the internal spring or detent that fails. So they made the switches throw aways.

We use silver plated copper bars in the equipment I work with. The bars carry thousands of amps, and I have seen some spectacular failures, where someone used sandpaper to "clean" the bus contact pads.

Sine · #7 05-25-2016, 09:32 PM

I too have restored a "broken" window by sinply cleaning the switch. A pencil eraser will get off the grime and corrosion, but leave the plating intact. Then, I just spritz it with some contact cleaner and put it back together.

Our diesels are between 20 and 40 years old - who wouldn't expect a little buildup? The next time I buy an old Benz, I will be doing this procedure to all the switches in the car. It's basically free, if you already have the pencil and contact cleaner.

jay_bob · #8 05-25-2016, 11:38 PM

Quote:

Originally Posted by scottmcphee

Odds are good the window control switch on the rear door needs attention. The center console switches for window control rely on good contact in the door switches themselves because power is routed through them while resting in their neutral position in order for central switches to have an effect driving the window motor.

If you disconnect / unplug the window switch in the door, the center console switch cannot drive the window up or down. That's just how things are wired.

Trivia: anybody know what will happen (without trying first) if the driver and passenger have a tug-o-war over the passenger's window by using switches in opposite directions? Keep in mind this is an old German car.

Is it:

A) the driver command always wins and overrides the passenger every time
B) the passenger overrules the driver's command every time
C) the driver command causes the passenger command to pause (halt) the window, then the first to let go is the loser, whoever holds longer eventually wins the window going in their direction
D) if the driver started the action the passenger's attempt is thwarted and driver's chosen direction keeps on truckin' and vise versa for the passenger if they started first
E) so long as either switch is in the down position the window keeps rolling down
F) sparks fly or a fuse blows if you're lucky, you just put 25Amps through two switches and created a dead short
G) the motor conjigulates as it tries to satisfy both commands simultaneously, and depending on the state of lube of the window regulator the window may slowly creep up, or down at a fraction of the normal speed
H) all doors unlock if they were locked, but the trunk and fuel door remain locked, and interior lighting goes on

it is answer C

The switches have a clever slip contact arrangement on their two contacts.
In the driver switch, the slip contacts have 12 V applied.
One slip contact is made in the "up" and "rest" position to the moving contact, and in the "down" position the moving contact touches a grounded contact point.
The other slip contact works the opposite way, the moving contact has 12 V on it at "rest" or "down" and is grounded for "up".

Hard to explain without looking at a diagram but here goes. If you have a diagram it is easy to follow the paths.

Switch at rest, both contacts pass 12 V to the motor, since both sides of the motor have 12 V applied, the motor does not run,
Switch in "up" position, one contact applies 12 V and the other contact applies ground. The motor runs since there is now potential across it.
Switch in "down" position, one contact applies ground and the other applies 12 V so the motor runs in the opposite direction.

The rear switch has the moving contact lines from the driver switch applied to its slip contacts. The moving contacts of the rear switch connect to the motor. The rear switch does not see 12 V directly, only the switched lines from the driver switch. The ground points on the rear switch are brought back to the console, but are interrupted by the child lockout switch, so if the child switch is open, the rear switch lost its ground, but the front switches still have a ground. So the parent can operate the window but the child can not.

The passenger switches are arranged so that if they are at rest, the voltages from the driver switch pass straight through the two slip contacts on to the motor. If the passenger switch is moved, one of the motor leads gets grounded and the other has 12 V.

If both switches are at rest, both legs of the motor have 12 V on them. Nothing happens.
Both switches moved in the same direction, motor runs in intended direction since the slip contacts apply ground (locally) and the 12 V from the driver switch to the motor.
Both switches moved in opposite directions, both ends of the motor winding have ground applied - no motion. No sparks, no drama, no blown fuses.

Wikkid Smott as they say up in New England.

This is true for 123, 124, and both generations of the 126.

Once you get to the 140/210 it is all on CAN bus and the door control module logic prevents this sort of conflict.

zu! · #9 05-26-2016, 01:28 AM

And here I thought it was all in good fun when my daughter complained it was stuffy and we played a game of who presses the button faster. It is a clever design though.

Scott, I'll have a look at the door switch. I never thought that it figured in how the driver switch operated.

Sent from my iPhone using Tapatalk

scottmcphee · #10 06-09-2016, 05:22 PM

Ugh. Same window stopped working.

After cleaning the switch on the door so carefully.

Going to clean the center console switch now.

zu! · #11 06-09-2016, 05:31 PM

Quote:

Originally Posted by scottmcphee

Ugh. Same window stopped working.

After cleaning the switch on the door so carefully.

Going to clean the center console switch now.

Oh. I'd forgotten to report back that I tried cleaning the switch and it didn't do anything. There was an odd looking resistor or something in the switch, that didn't seem to be connected to anything. I wonder if it was burnt. Did you see anything like that Scott?

I should've taken pictures, but I had such a hard time getting the little balls to play nice whilst I tried to jam the switch together I completely forgot.

Demothen · #12 06-09-2016, 06:00 PM

If the switch you are talking about is for a w123, there should be a resistor that connects to the light bulb inside each switch (at least on the center console switches).
Fyi, I cleaned all of my w123 switches roughly a year ago using contact cleaner and a small flat screwdriver to scrape them. I just had to pull them all again and repeat because I started to have intermittant failures again. Lots more carbon was built up on the contacts. I agree that using something like a pencil eraser might be a good idea, rather than scraping like I did. I may try some contact enhancer to see if that buys me more time.
I wonder if the silicone dielectric I used might have caused problems...