rear (De mister)heater

[Suki]

Hi All,
My dad seems to think that I am now his personal assistant!
He wondered if anyone in the forum knows how to fix a rear demister in an s class!
Now only 2 lines are demisting. He told me in the past that people used to use conductive paint where there was a break but he is not sure he wants to do that on his s class.
Are there any other suggestions?
Thanks in advance.

Suki

 

[wireman]

Fit a new glass, any other repair will no doubt fail.
The conductive paint used for these kind of repairs can tend to have poor electrical contact with the existing coating and a local hot spot can occur, this will blow out the rear glass.
Your insurer may wish to contribute to the cost.

 

[shayes]

Hi All,
My dad seems to think that I am now his personal assistant!
He wondered if anyone in the forum knows how to fix a rear demister in an s class!
Now only 2 lines are demisting. He told me in the past that people used to use conductive paint where there was a break but he is not sure he wants to do that on his s class.
Are there any other suggestions?
Thanks in advance.

Suki

Difficult to know why this is the current symptom with my newly acquired W140 - S320.
Used yesterday and suprised only two lines seemingly demisting. These cars cost the earth and my previous SEL was great for demisting. Can't see that the electrical circuit can break as unlikely any owner would trash their rear screen internally. Or, could there be several circuits for the panel? Anyone know the cause of the problem?

Thanks

Stuart

 

[television]

Sorry these circuits are only one.

 

[roofless]

Fit a new glass, any other repair will no doubt fail.
The conductive paint used for these kind of repairs can tend to have poor electrical contact with the existing coating and a local hot spot can occur, this will blow out the rear glass.
Your insurer may wish to contribute to the cost.

i have seen this in the past with the paint on type of repair .a hot spot & no rear window as a result .wireman is right but it's worth asking mb if it can be repaired

 

[shayes]

have read that it could be the relay, perhaps switching off too soon. Did notice the light had gone out but not really noticed how long it stayed on. Awaiting CD on this car to better understand the relays and wiring. Funny how they put double glazing in the side widows which is great, and yet not a double glazed rear screen which would be a real benefit to all cars in colder climates.

If not the relay than a poor mans solution would be to fix a small fan to the shelf and connect to the demister cable - bodge and go - no mustn't go there!!

 

[wireman]

The modern type of heated rear glass uses a condutive paint in wide stripes verticaly at the edges, one strip goes to ground the other to the supply, the heating strips are connected between each of the vertical strips and get almost full battery/alternator voltage applied to each of them. If a careless or clumsy git cleans it with a dirty (microscopic grit) cloth the heating elements are at risk of damage, dont use abrasive window polish since that will also kill it.
Putting long loads into the vehicle and clonking the rear screen also puts each strip at risk, quite common in hatch backs and estates where the door is used to push or hold the load in.

The electrical circuit is basicaly, fuse from battery to relay contact, other relay contact to rear screen, rear screen to body/ground/earth, to control it the switch is connected to the timer relay (not directly to the glass) which derives its supply from the ignition switch.
The relay should stay on for 10 - 15 mins or there abouts.

Its best cured with a new glass, the insurance exces is usualy 50 quid or so.

 

[television]

As wireman for the best part,, the timer part is in the heating control unit in the center of dash, the output goes to the relay in the N10 relay, and from there to the screen.

the push button units can and do get dirty contacts on the press button switches, but if the lamp id on the rear window usually is too