Rear Defroster Problems

[ehs1331]

Hello All,

Im new to the site and it looks great. My wife has had her 2001 Beetle GLS for a few months now and has noticed the rear defrosters doesnt work. I have checked the fuse and it is ok, the switch lights up when depressed. I have also removed the rear hatch trim and checked the wiring to the grid. I have 12 volts on the the wire on the passenger side of the grid and nothing on the wire to the other side of the grid ( diver side ). should you have voltage on both sides? Please help, she is driving me crazy about this.

Thanks for any help,
Eric

[IndyTom]

I really don't know much about the rear defroster but from what I read it could be the switch itself that is defective.

Here is a link to the TDI club that may help you:

Rear defrost doesn't work - TDIClub Forums

[simonsi]

Originally Posted by ehs1331

Hello All,

Im new to the site and it looks great. My wife has had her 2001 Beetle GLS for a few months now and has noticed the rear defrosters doesnt work. I have checked the fuse and it is ok, the switch lights up when depressed. I have also removed the rear hatch trim and checked the wiring to the grid. I have 12 volts on the the wire on the passenger side of the grid and nothing on the wire to the other side of the grid ( diver side ). should you have voltage on both sides? Please help, she is driving me crazy about this.

Thanks for any help,
Eric

Hiya - I'm not sure if the switch switches 12V or ground on these cars but some simple tests will show you:

Switch the defroster OFF - If you have 12V on one side of the defroster then it looks like the switch is switching ground and may be bad. Unplug north wires onto the defroster grid, turn the ignition on and start the car. See if either wire responds to switch input, firstly do you see 0V going to 12V and back to 0V, if you don't see any voltage change and you have no 12V see if you get a resistance change on either side when you cycle the switch. If you don't see any response then the switch or its associated relay are bad.

[ehs1331]

Thanks everyone. will test it out in the morning and report the out come.

[ehs1331]

well couldnt wait untill morning, braved the cold to check it. i pulled the lead off of the left and right side of the grid. when the switch it lite and depressed the passenger side lead has 12v and the drivers side has nothing. swith not depressed there is 0 voltage to both sides. Should both leads have 12v? I checked the grid and it has only 190 kiliohms when connected to both leads. i didnt see any damage to the grid. I also tested down the side of the grid where there are several areas that ties into the fine wire that runs across the entire grid. it has 12v everywhere I touched my probe, the adjacent drives side in the same areas had 0v.


if only 1 of the fine wires running across the window is damaged, would that render the entire grid usless? one looks a little funny but it is intact.

The window has tint on it. I dont know if that has anything to do with my problems.

Look forward to hearing back,
Eric

[geniushanbiao]

I think the 2 leads should be one 12V one ground. Two 12Vs will not make it work. But you have to check the continuity of the ground. There is another easier way. Simply use a light bulb and connect the 2 leads to a light bulb. If it lights then the power supply is good. Don't use voltmeter sometimes voltmeter tells you 12V between the 2 leads but it can't make the defrost work.

[simonsi]

Ok, 1x 12v and 1x ground.

Unplug both wires from the grid, measure resistance on the wire that didn't give 12v at any time with one meter probe on the wire and the other meter probe on a good ground point on the bodywork ( a bright unprinted bolt head is usually good), my guess is you don't have a good connection on that wire to ground, hence no current can flow, hence no defrost.

If that is so then you will just need to repair that connection to ground (or run a new one making sure you use wire at least as thick as the factory), and all should be good.

If the ground connection is good then either the grid is broken or not on long enough to heat up. How long is it driven with no apparent defrost action? You need some good current flow to heat the grid, your resistance measurement is too high for any effective current flow.

[ehs1331]

well guess it is the window. no broken pieces of the element I can see. Some color change on some of it. I have good ground and voltage to the window. at any point of the horizontal grid (thin strips) all reads 0 volts, tested my car and it reads 12 volts in the same areas. have good power and ground to the grid so I guess she is just out of luck lol. not replacing a window for a defroster. probally to much to spend. Thanks for everyones help. Oh, i have had it on for atleast 30 minutes. Thanks again.

PS: this is a great site!