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kemestry
11-07-2007, 01:05 PM
Okay ... sorry about the multiple posts but I thought that each issue might warrant a separate thread.

My rear defogger isn't working for some strange reason. Looked at the fuse, its good. Other than that, I don't know where to look. Please give me a starting point as to what could be the problem because I need it to work for the winter.

Mike

T.Dot_E30
11-07-2007, 01:09 PM
The defog switch is a common point of failure.

Use a test light, test for power, going to the switch and also coming out when its on.

Then test for power at the rear window, if you have power....your rear window probably needs to be replace with a new one since the lines can't be replaced..

kemestry
11-07-2007, 01:33 PM
The defog switch is a common point of failure.

Use a test light, test for power, going to the switch and also coming out when its on.

Then test for power at the rear window, if you have power....your rear window probably needs to be replace with a new one since the lines can't be replaced..

Thanks, but is the switch by the rear window or the one on the dash?

Mike

markw
11-07-2007, 01:41 PM
dash

craz azn
11-07-2007, 04:21 PM
I also have a rear window if you will need one. 30$

Engin33r
11-07-2007, 05:39 PM
The defog switch is a common point of failure.

Use a test light, test for power, going to the switch and also coming out when its on.

Then test for power at the rear window, if you have power....your rear window probably needs to be replace with a new one since the lines can't be replaced..

Umm, if you measure 12V across the window that means it is working fine OR itís broken. Bad way to debug! The proper way to test it is to measure from the half way point to ground and measure anywhere from 6-7V. The lines act as a load which intern heats up. The window is the only load on the circuit, and since they run in parallel all the lines would be equal. Tie ur DMM to the passenger side and drag your + lead on the DMM across the lines to the drivers side. Youíll go from 0 to 12V

Try this first before trying to debug.

Pull off the spade connectors and replace the female ends with new ones. (Throw some black heat shrink on to make it look pretty)

Now take some emery cloth and sand the male spade connectors on both sides of the window. If you are up for it, tin them with a soldering iron. Then put it all back together.

What you can find is that using voltage as your primary reference is not correct. Measuring the current is best, but, unless you know how to measure current through a shunt, itís not possible in this application because most every multimeter is limited to 10A. the defrost circuit is rated at 30A.

So, that being said, your problem can exist from a poor connector, ground, or switch. Because E30 donít use a relay, youíre dependant on the switch securing a good enough connection to allow for 20-30A to flow. If you have a faulty switch, it will also have a voltage drop. Pull out the switch but donít disconnect it. Turn it on (& the ignition) and measure the voltage between the thick black & thick green wires. You shouldnít have anymore then .5V. if you do, then you may have found the problem.

I did all this last weekend and found that it was a combination of things which made it lousy. Now it works fine, but still doesnít get as hot as Iíd like. This is my first winter in an E30, so I donít actually know if itís supposed to heat up to the point where itís hot to touch on the inside.

Good luck.

Oh, and just as an FYI, lines can be repaired if they are scraped open.

e30_kid89
11-07-2007, 08:00 PM
i have a rear window too if you want, they're supringly easy to swap out. $25:P

Oh but i have to see if its cracked or not.

Ej_Red
11-07-2007, 08:31 PM
I'll take that window from you if the defroster works on it?
Can i test it to make sure it works before i buy it with a 12v battery?

Ej_Red
11-07-2007, 08:37 PM
Engin33r, if you apply red lead to the driver side connector/power and black lead to a good ground and you get close to 12V switch is no the problem. I wouldn't even check the switch due to applied voltage fully delivered to the terminal.
He can check for voltage drops through every grid, it should be close to 12V on the live circuit of course. If it's way less then close to 12V there is too much resistance; therefore not enough current to heat up the grid.