W124 coupe heated rear screen broken

[Don777]

I've just bought the this car and the heated rear screen isn't working. No light comes on in the switch either. I've checked the fuse and it's ok. I was trying to get at the terminals to see if there's any voltage but I was worried about breaking the trim. Is it ok to pull the rear pillar trim off or will I break plastic poppers? I get the feeling that there won't be any voltage at the terminals because of the lack of a light in the switch. Is this indicative of something obvious like a relay fault maybe or a duff switch? If it is a relay, where is it?!!

Sorry there's so many questions but I'm new to Merc's and the W124...

 

[television]

I will look into it Friday

Malcolm

 

[television]

Hello again, your window looks very simple, I cant find any relay so it looks as though the wire goes direct to the rear window element that is possible to change. as the LED is not on it should be just a fuse, with luck.

Malcolm

 

[pascal]

I have a bad memory, but am pretty sure there is a relay.

Look on your fuses diagram. There are 2 seperate fuses.

If the fuse for the element was gone, the light on the switch would still illuminate, but heater would not work. It seems that you have the opposite. The relay and switch have a shared fuse, i think.

I got to go out right now, but I am pretty sure i did a post on this before.

 

[pascal]

Okay its controlled by the combination relay:

And it looks something like this.

They are pricey enough because they control wiper/wash and flasher also. Some guys have repaired them, as the solder is inclined to crack sometimes. It is found behind the firewall, near the battery

But check the fuse (the low amp one) first.

Pascal

 

[television]

I have a bad memory, but am pretty sure there is a relay.

Look on your fuses diagram. There are 2 seperate fuses.

If the fuse for the element was gone, the light on the switch would still illuminate, but heater would not work. It seems that you have the opposite. The relay and switch have a shared fuse, i think.

I got to go out right now, but I am pretty sure i did a post on this before.

the diagram shows the switch with a cable that goes direct to plug/socket on the screen
I have checked all relays in box nothing there, also you cant have a relay before the switch.
As the current through this switch is quite high, the switch could be faulty.
I have spent 1 hour searching

Malcolm

 

[pascal]

Well it may have changed in the 95 model, but I find it hard to beleive that there is no relay.

 

[television]

Well it may have changed in the 95 model, but I find it hard to beleive that there is no relay.

Me too, but after your posting of the relay it could come from an already closed relay, but even then all of the high current is passing through the switch. Also I have never known of an element that you can change, its the same size and shape as the rear window.there are no differences shown for year maybe its a very low current demister

Malcolm

 

[Don777]

Thank you all for your answers, but would you believe it decided to start working all by itself! I got as far as getting my voltmeter out and thought I'd check the switch one more time and....hey presto! Fingers crossed it'll stay that way.
Unfortunately the drivers side headlight wiper has failed, so I may post on that.
Thanks again.

 

[pascal]

Don
well the wash/wipe feature on your car works on that same combination relay as far as I know. There would be no harm removing it, clean its contacts, and replacing.

 

[Bolide]

Heated rear window

IIRC the heated rear window uses a non-latching switch, a timer, relay and led. The switch tags the timer & relay, which feeds the screen & the led. When the timer expires the relay releases & the led & hrw turn off

The clue is the non-latching switch with led. When the led goes out it means the hrw is off

If you turn the hrw on, turn off the ignition & then turn it on again, I think the hrw is then off. Either way it's designed to prevent you from leaving the hrw on all the time


Nick Froome
www.w124.co.uk

 

[Don777]

the wash/wipe feature on your car works on that same combination relay as far as I know

Thanks Pascal,

I will find it and clean it as you suggest and report back.

 

[television]

Sorry that so far cant find any relay, Very simple to find though.
Lift the bonnet, put your ear close to the relay box and have someone turn on the HRW and you should hear the click,or if you cant hear it you should be able to feel it, then as Pascal says take it out, have it re soldered and cleaned. I will keep looking for it. As Bolide says there is the timer. On later cars the switch is in the AC unit where it goes onto the N10 relay,this is standard on W140 and R129 and many others. The diagram from WIS shows the switch with cable and plug that goes to HRW, If there was any print out facility I would put it up.

Malcolm

 

[Bumper]

Below is a picture of the relays, the one marked H is the combination relay for heated screen, wiper motor and turn/hazard signal . The relays will be positioned on the drivers side of your car. I can also list the other relays in this cluster if you want.

 

[Don777]

Thanks Bumper, I've been away for a few days so didn't have a chance to have a good look.
Is it likely to be a relay if only the drivers side headlight wiper is not working?

A list of what all the relays do would be great too!