w204 rear demister only clears centre portion of window

[MancMike]

Hi,

So today was the first properly frosty morning since I've had the car and I've noticed two issues.

Firstly, when the rear demister is on, the radio is just hissy noise. Can this be fixed? Is it normal?

Secondly, the rear demister only clears a portion of the screen. See photo. Again, same two questions!

 

[st13phil]

Firstly, when the rear demister is on, the radio is just hissy noise. Can this be fixed? Is it normal?

No, it's not normal and is almost certainly related to...

Secondly, the rear demister only clears a portion of the screen. See photo. Again, same two questions!

Again, not normal. Suspect that there are one or more of broken heating elements on the screen. Solution will be to replace screen.

 

[clk208]

Became a convert to running AC continuously year round in cars a few years ago and haven't seen a misty rear screen for a long time since.

Might be a short term workaround til you get it repaired anyway..

 

[MancMike]

My AC is also broken

Is there nothing I can check/clean? A dirty contact, or something?

 

[markmifsud]

If you can find the break in the heater wires, you can try to join the breaks with conductive paint

Electrically Conductive Silver Paint | Maplin

 

[MancMike]

Thanks. So the heater wires are bare then on the back of the glass? not insulated? So I'd be able to trace around with a multimeter to find the break?

Thanks.

 

[Ted]

If the elements ARE printed on the surface of the screen, this is how to test.

Use a testlight not a voltmeter.
Connect one side of the testlight to a known good earth.
Run the blade or point of the testlight down the middle of the screen on the elements. You may have to push hard to cut through any insulating layer.
If the testlight glows half brightness the element is good and working.
If the testlight glows FULL brightness there is a break between the point you are testing and the return. Keep testing to the point where the testlight stops illuminating. This is your break.
If the testlight does not illuminate, there is a break between the supply and the point you are testing. Keep testing towards the supply until the lamp glows full brightness.
This is your break.

Seemples

 

[MancMike]

Well this fixed itself. :S

Turning the demister on doesn't screw up the radio any more.

Although I'm not sure if that's because the demister has stopped working altogether! Will check in the morning.

Also, my left RVM doesn't seem to be getting hot. The right one gets hot to the touch and clears in less than a minute, but the left one stays wet and doesn't seem to get heated much at all.