W124 window problem
 

I have a 1991 W124 esate, that has been sitting for some time.
The front passenger (UK model) window motor is permanetly running inthe down direction, I have checked the wires in the door and they are permanently live. I have removed the console switch, but this has made no difference and checked the relay under the bonnet, which seems fine as the other three windows and sunroof operate correctly. As this is a permanently live circuit I am assuming it could be an earthing problem, any suggestions?

Starting in 1990 the W124 chassis has a computer under the rear seat that controls all of the window functions. Including closing them with key held to lock position.

Sounds like that computer is the root of your problem.

Hi M.B.DOC, can you confirm that is also the case for the estate, I have looked under the rear seat squab, but there is nothing there, would it be somewhere in the rear of the car?

The air-pump is under the passenger side of the rear (center) seat cushion, IIRC the conveinence module (or whatever it's called) is under the driver's side.

Babymog, I think that is the case for the saloon, but not in the estate, 'cos I can't find 'em!

My '91 300TE / Estate had them there, but that's US delivery, ... Your car might be different.

Your pulling up the carpet etc., correct?

Err no, I'll try that next then.

Found it!
Had to cut a hole in the carpet.
Relay #6 keeps locking up in a closed position, all the others working fine. If I wedge it open, then the switch works to open the window, but if I manually close relay #6, then it also blows a fuse. I have checked the earth wire to the motor for continuity and it is fine, so I guess this module must be faulty, doesn't look cheap to me and I suppose it's not repairable, (If I knew where/what the fault was in the first place!)
I don't suppose there is any way to test it before replacing it?

Used parts are the way to go.. was fitted on W124 chassis 1990-95 & on W202 C-class from 1994 to 1997

When I search for the 124 part, this is what I found.

2028200926

Mercedes (OE)
AC Control Unit; Comfort Control Unit
Please verify Mercedes part number on existing unit prior to ordering. 1 per car. Special order item - limited availability.

You should check the EPC and see if the parts are the same or if one replaced the other one.

I would say that it is based on what MB Doc says in his post.

OK, so I have checked it out with all wires connected. For the front right and both rear windows, relays 1 to 4, 7 & 8 all work correctly. When the front left switch is pressed down, relay 6 activates and stays closed, even when the switch is released, I can only release it by physically pushing it open, when it stays open. When the switch is pressed up, nothing happens, relay 5 should close, but it doesn't.