Heated Rear Window Problem 2000 W210

[gasman59]

Hello All again:

This is a 2000 E320 (W210), sedan.

This morning I noticed the rear window heater (demister) is not working. It was on for a 10 minute drive and the fog/mist did not clear up at all.

Here is what I tried today:

I placed a 12V lamp (1157 stop lamp) wired between the two sides of the window alligator clipped to the area where the wires attach to the window elements. The lamp cycles on/off with the demister switch. The wires appear to be firmly attached to the window.

I inspected the elements and they all look perfect. No cuts, breaks, or any other apparent damage. Since the lamp lights I suspect the elements are shot.

Is this a correct assumption, or have I missed something?

The previous owner had an aftermarket tinted window treatment installed on the rear window.

Thank You,
Ron Y

 

[bigasotonuk]

Hi,
I agree with your conclusion, the window element is shot.

 

[television]

The chances are that the element is between the glass, or is your surface mounted

 

[gasman59]

Hi Malcolm:

Surface mounted elements (inside).

Thanks.

 

[kid-jensen]

Gasman,

Get yourself a cheap DMM, form Maplins, CPC or whatever. Attach one probe to one of the terminals, and slide the other one up and down the "wires" attached to the screen. With the DMM set to low resistance range, it should show a figure around 5-10ohms at the mid point of the track on the glass. You may have to screpe the track (CAREFULLY!) to get a good connection. Having got a esensible reading on one o fthe tracks. you should then be able to identify where the break is (usually caused by a sharp object scratching the glass inside). If that's the problem, it can be repaired with conductive paint (CPC).

You can get a situation where the whole element goes high-resistance over the years (change in chemical composition with time) and eventually refuses to warm-up.
In this situation, it's down to bribing a local vandal to come round with a brick! (only joking of course......)

 

[jberks]

I could understand if one strand was broken. It happens, but all strands, nah. If, as you say, there is current and a -ve then at least some of the window should work. It's on;y a bit of resitstance wire so if there is continuity it must be working. Telling if its working howeverm is a trickier proposition.

Daft question. How much condensation is it trying to shift? If, for example, you had a dirty window and something rather damp in the boot, then it may just be that whist it's working fine, it's been overwhelmed.

I'd start by cleaning the inside of the rear window. It may look clean but I was surprised how much muck I got off mine last time despite it looking clean. The tell tale was that it started misting up. In my experience, if you have the aircon on (as you should at this time of year) and the windows are clean, you should almost never need the demister anyway. I use mine maybe once or twice a year. Any more than that and the windowlene comes out.

 

[television]

There are loads of kits on the market to fix it

Just Goggle heated rear window kit

 

[type49]

Could be a poor earth on the C pillar. May be good enough to light your bulb but when asked to be loaded with big amps that the HRW draws, it cant manage it. Worth checking for free. It's behind one of the pillar trims, fixed with a 10mm nut.

 

[gasman59]

Hi All:

Thank you for taking the time to aid my diagnosis.
I will try your suggestions this weekend and of course report any findings (and hopefully the resolution) for others advantage.

One thought is to open the ground side and see if the lamp lights via the elements (at least it would prove continuity).

At times the car sits for a few weeks due to my significant business travel. We just came off an unusually warm/wet fall in the north east US and suddenly have plunged below freezing. The car was a bit damp really misted up during this short drive.

Best Wishes,
Ron Y

 

[jberks]

At times the car sits for a few weeks due to my significant business travel. We just came off an unusually warm/wet fall in the north east US and suddenly have plunged below freezing. The car was a bit damp really misted up during this short drive.

Best Wishes,
Ron Y

Ah - been there. Left my car in an open air carpark one winter whilst I went away, it was really damp as a result and misted up spectacularly. An hour's drive later, with the aircon on and most of the moisture had gone. I'd give it a few days of normal use and see what happens before stripping anything down. I still suspect it's simply that the window element was overwhelmed. It can happen, I used to get it for a day or two after shampooing the seats. Soon cleared up.

 

[television]

Ah - been there. Left my car in an open air carpark one winter whilst I went away, it was really damp as a result and misted up spectacularly. An hour's drive later, with the aircon on and most of the moisture had gone. I'd give it a few days of normal use and see what happens before stripping anything down. I still suspect it's simply that the window element was overwhelmed. It can happen, I used to get it for a day or two after shampooing the seats. Soon cleared up.

Good point, the water can run down to the sound deadening material and take a long time to dry

 

[gasman59]

Hi Jberks:
I guess I am missing something here.
My datapoints are our other cars. One German (BMW) and two American SUVs.
On all of these cars the rear window heaters not only clear mist quickly, they actaully will melt snow!
Is the Mercedes designed differently? Lower power?
Just curious.
Thanks,
Ron Y

 

[television]

Hi Jberks:
I guess I am missing something here.
My datapoints are our other cars. One German (BMW) and two American SUVs.
On all of these cars the rear window heaters not only clear mist quickly, they actaully will melt snow!
Is the Mercedes designed differently? Lower power?
Just curious.
Thanks,
Ron Y

vertical screens normally clear faster than sloping

If you put a ammeter in series you can work out if it is working correctly and the wattage

 

[jberks]

my experience is that merc screens have thinner wires closer together than other makes. So, in theory I guess each wire is cooler but overall the effect could be the same. That said, I would agree that I have had cars with more effective demisters, certainly at clearing condensation on the outside. Ice does clear but it takes a bit longer. Inside fogging as I've said before, only really occurs if I have the aircon turned off or the rear window is in need of a clean.

 

[gasman59]

Oh Boy:

Looks like the worst news.

All connectione were tight so I unscrewed the ground side and installed my test lamp between the elements and chassis ground. No lamp action with demister turned on.

I then placed a DVM in line without the lamp and read 12.8 volts.

Tried the lamp between both sides of the element, it lights as before.

I tried disconnecting the 12V side, (after attaching the ground side back to chassis), and still no lamp, 12V to element.

My conclusion, there is no significant current through the elements.

I priced a new rear window. "Ouch". For now I will try an inexpensive, OEM looking aftermarket element first.

Guess I will have to remember to stay below the antenna portion.

Thanks for all the guidance.

Ron Y

 

[television]

Do you know what system your car has, it cant be motronic it think