Rear Demist Not Demisting

I connected up my rear demist last weekend and have had a couple of chances to try it out, with not a lot of demisting going on.

I've got 12V at one connection and an Earth at the other. I can measure 1.6kOhms across the screen, so there's a connection with resistance through the element.

What else can I check?

 

1.6k is strangely high - not going to get much heat out of that (it's only 10mW)! I'd expect a heated rear screen to be in the order of low single ohms.

 

Yes, I suppose so. The elements all look in one piece, but will have a closer look.

 

Have a good look. Summut's broken somewhere, or maybe the terminals aren't stuck to the tracks properly.

As you likely know, they are fixable with conductive silver paint.

 

Yes, but no obvious breaks so will take a look at the terminals when I get a nice day!

 

^^^ whs Just checked a spare element I haven't quite got around to fitting and that gives a reading of 1.4 Ohms

 

That'll give you 102W, which is pretty heaty

 

It's probably broken down with age and UV....

I fitted a new heated rear window to a beetle a number of years ago now, and that was originally measuring k ohms... I can't remember what the new one read ohm wise but it was very low, and I had to upgrade the OG wiring, as it was getting super hot and blowing out the 8amp fuse, so I upgraded it to 16amp wiring and fuse, and the wiring stopped heating up

OG bay hrw wiring is super heavy... 40amp rated wiring from what I've seen!!

 

Yes, got the OG wire still in place but the element may be toast.

 

Toast is going to be a lousy conductor of electricity