rear defogger...

[BrianL]

I need some help with my rear defogger: The switch works, and power flows through the lines in the glass, but the rear window stays foggy in the morning. I have an old voltmeter and determined that around 5 V flows through the lines both from the glass to the ground (drivers side) and from the hot-wire (red-black wire on passenger side) to the ground. My Haynes shows that there is a 20A fuse between the glass and defrost switch, but since everything gets power that fuse must be intact. Will the glass physically heat up to the touch if it is working properly? Maybe I don't have enough power flowing through… If that is the case then maybe the lines are corroded somewhere along the way? Oh, also when I turn the switch on and off the ammeter in the dash shows no change. Any theories and/or ideas are appreciated. Solutions are welcomed as well! Thanks guys. -BrianL

[Z-Priv]

i have the same exact problem as you. Probably as do others.. I'f i figure it out i'll let you know what i did.. I too am getting power to the window but stays fogged up until the inside of the car finally warms up enough..

[BrianL]

Hello All. I believe I've figured out the reason why it doesn't work: IT'S 30 YEARS OLD!!! I replaced the rubber seal around the glass and thought that would also be a most favorable time to fix the defroster as well. I had planned to replace with new glass if I couldn't figure out or fix the defroster problem, and after calling several local auto glass shops as well as Motorsport, found out that replacing the glass is not really an option. When I had the glass out I was able to get a close look at the underside of the defrost lines in direct sunlight. They were (are) covered in black corrosion ( or 'stuff'). I carefully worked on a small section with steel wool and a razor blade; in some places I was able to find metal, but in others it was all black stuff.

I have owned this car for about 6 years, and when I first got it the rear defroster worked, then after a year or two the orange switch busted. About another two years went by before I got around to replacing it (still didn't defrost) and now not a single line will carry a current. Weird. (Maybe it was those two lost years at Humboldt? Lots of rain up there…).

The bottom line is it doesn't seem to be something that is fixable; although I had toyed with the idea of getting 'that metallic tape' one can use to fix small sections of missing defroster line and re-doing the whole rear window with it… I doubt it would come out straight, and my hands need to heal anyway.

[Z-Priv]

that doesnt sound too promising.. .. will look for black stuff on mine.

[SMW]

I ran across another option for rear window clearing on the web:

http://www.zspecialties.com/hotdeal.htm

It is basically a small electric fan and heating unit that runs from the same wiring that led to the wires on the window.

I was going to order it, but I'm still dealing with some engine trouble, and that comes first.

Might be an easier way to go than trying to locate a small break somewhere in the 30 year old wire.

Steve

[EScanlon]

The defog unit works by resistance. The wires in the glass actually resist the current and hence heat up. You want to make sure the contacts have been cleaned and free of corrosion, so that the current delivered to the wires is unimpeded. Don't muck with the "black" stuff this may be the adhesive for the delicate and thin metal film that's been applied to the glass to generate the "wires".

If you have good wiring, switch and fuse then you should be feeding a full 12v to the defog, and then you should be generating the full amount of heat from the resistance in the wire. If you aren't getting a full 12v then that's where your problem may be.

[Daniel]

The first rule of race car driving is whats behind me doesn't matter! From the movie gumball rally.On the serious side.The haynes book says use dupont#4817 to repair the bad traces.My 1990 service manual for my 300zx page EL-84 shows the same dupont number.Its shows how to test and repair bad traces.You use a ruler as a straight edge and a drawing pen to apply the silver.Any good art supply store will have the pen.Your local nissan dealer should the 90 300zx service book and could point you toward the dupont#4817.It looks to be an easy job.When job is complete ,dry with a heat gun or air dry 24 hours.If you can't find the book let me know and we'll work that out.Oh yeah I think the "black stuff"is oxidized silver,just like granny's old tea pot. Have Fun!! Daniel

[TomoHawk]

Actually, it's a defroster. It's supposed to melt the frost off, so if it's fogged up, you need to use a fan like your windshield uses.

[Zvoiture]

Fortunately for you, tomohawk's don't have rear windows!

steve77