Car rear window demister not working

C

ClubMan

Registered User
Messages
50,568
My 142 Dacia Sandero rear window demister is not demisting even though (a) all fuses are fine (b) power (14-15V) is getting to the demister "tracks" and (c) there is no break in continuity in the "tracks". So everything looks fine but it simply doesn't demist the window (or very barely does - maybe a couple of mm either side of the window "tracks"). Any ideas?
 
Not a mechanic but maybe a bad electrical connection somewhere on the circuit that is not letting the required amps through.
Possibly corrosion where the earth wire coming from the demister is bolted to the chassis. Or a corroded contact in the switch for the demiser. It might be possible to find the bad connection and give it a clean with a wire brush. And spray a bit of Wd40 on it after.
 
Thanks. I would be surprised if there was corrosion as the car is not that old and in very good nick with no sign of any moisture ingress anywhere that I can see. But I will try to investigate the circuit and see if I can find anything wrong. On the other hand I did commit the cardinal sin of leaving a wet umbrella in the boot not too long ago and that may have coincided with the problem and maybe THAT caused some corrosion... Thanks again for the suggestions.
 
Are ALL tracks producing some sign of heating, ie. some demisting occurring around EVERY track?

If not, I strongly suspect that you have a break in the grid somewhere.
If they are, lets hope it is a simple as a 'gammy' earth.
 
I remember years ago repairing the rear window heater of a Ford Cortina with stuff from a "nail-varnish" type bottle. I'm uncertain at this remove if I was sticking the "tracks" to the glass or repairing breaks in said track. Try motor factors but I doubt you can get the stuff any more.
 
mathepac said:
I remember years ago repairing the rear window heater of a Ford Cortina with stuff from a "nail-varnish" type bottle. I'm uncertain at this remove if I was sticking the "tracks" to the glass or repairing breaks in said track. Try motor factors but I doubt you can get the stuff any more.
Click to expand...

I think you can still get it, a conductive liquid that dried forming a 'bridge' over any break/crack in the track.
Mixed results, anecdotally, I heard of a guy who 'popped' his rear screen by the repair generating a hot spot and therefore thermally cracking the glass.
 
Unfortunately Leo's stuff is not much use to you @mathepac as it's water soluble.

Good choice https://www.amazon.co.uk/s?k=demister+repair&i=digital-text&ref=nb_sb_noss_2 (here.)
 
  • Like
Reactions: Leo
SparkRite said:
Unfortunately Leo's stuff is not much use to you @mathepac as it's water soluble.
Click to expand...

I didn't notice that! Thanks.

I bought non-solvable stuff years ago from a UK electronics supplier that has gone out of business since, I linked RS as it was the only link that popped up in a search. I usually avoid them as they're expensive compared to most of the competition.
 
ClubMan said:
My 142 Dacia Sandero rear window demister is not demisting even though (a) all fuses are fine (b) power (14-15V) is getting to the demister "tracks" and (c) there is no break in continuity in the "tracks". So everything looks fine but it simply doesn't demist the window (or very barely does - maybe a couple of mm either side of the window "tracks"). Any ideas?
Click to expand...

The voltage might be getting through to the tracks but the required level of current might not.
In that case there is not enough power driving through the elements.
Elements might be wearing out ?
Might be easier in the end to get a new demister.
This is a lousy time of year to be without an effective demister.
 
DirectDevil said:
The voltage might be getting through to the tracks but the required level of current might not.
In that case there is not enough power driving through the elements.
Elements might be wearing out ?
Might be easier in the end to get a new demister.
This is a lousy time of year to be without an effective demister.
Click to expand...
Thanks @DirectDevil.
Haven't got around to checking this again but I think that I need to check the grounding and the current alright.
It does eventually demist but it's very very slow and used to work a lot quicker.
I doubt that it's wearing out - it's only a 142 with very few km on the clock so hardly used.
If it did need a new demister then I thought that that meant getting a whole new rear window? :oops:
 
ClubMan said:
Thanks @DirectDevil.
Haven't got around to checking this again but I think that I need to check the grounding and the current alright.
It does eventually demist but it's very very slow and used to work a lot quicker.
I doubt that it's wearing out - it's only a 142 with very few km on the clock so hardly used.
If it did need a new demister then I thought that that meant getting a whole new rear window? :oops:
Click to expand...

If it's not demisting as quickly as it did then it would follow that the current drawn will be down. But down on what? Do you know what the current draw should be?

They do not 'wear out' as such, either there is a break somewhere or a bad connection.

You are correct, to change it you do need a new glass. That is assuming you want to do it properly and not try some third party add on effort.
 
You must log in or register to reply here.
Back
Top