Help Troubleshoot Rear Window Defroster

No resistance means there is at least one break in the grid. If you can find the break it can be repaired with a kit. If it is many breaks - look for another rear window.

What are you using to measure the resistance?

He asked what resistance should be - so has to be an ohm meter vice a simple "if light turns on circuit is complete"

You should be able to f>

Electronic Ohmmeter. I show it completely open (no resistance). I'll have to start tracing for a break somewhere. Yippee. It's so fun trying to fit my

Larry

Completely open circuit is infinite resistance, no?

An example of no resistance would be the circuit across Shaggie's teeth. (He wears metallic orthodontic appliances, for those who aren't aware.)

-Rob

No, no resistance is 0, infinitive resistance is when the meter does not display any ohms - open circuit.

I was asking because a surprising number of people either don't have a good digital multimeter, or don't know how to use one. Poor instrumentation or lack of knowledge on how to use it is a big part of not being able to suss what's going on with electrical stuff. I've had guys assure me that they could do their own troubleshooting, and that they had a good meter. They come back to me on the phone and say, "Okay, so this meter has a red wire and a black wire . . . how do I use them?"

When you reported that you measured open, what exactly did the meter say? Was it a digital type that just displayed the same as if you had not hooked your test probes to anything? Was it a gauge-type and the meter didn't budge? And were the feed wires disconnected from the attachment posts on the window when you took the reading?

"Ben Boyle" wrote

It's pricey, but Motorworks lists the window for '65 to '71 Beetles:

I haven't seen the '72-up windows anywhere. :-/

-- Scott

Hiya RGVAC,

A couple of years ago I purchased a rear window with defroster grid for my 1970 Bug. I went through my local VW dealer. They ordered it out of VW's regional warehouse in the LA area. I was told at that time that it was the last window they had in inventory. It may well be that RMMW has them in stock. Then again RMMW does have a reputation for listing parts in their catalogs which they do not have (in stock).

Mike

OUCH!! For $300, I'll stick my son in the backseat with a dry towel!!!

Actually, if I can't locate the break in the current grid, I'll simply pop one of JC Whitless' rear window defogger fans on the rear speaker shelf and be done with it!

Larry '71 SB - "Herman"

.................I haven't tried that but I know that others who have say that it works very well.

Wow, I'm amazed. This is the first time I've ever heard someone ask this question, and IT'S EXACTLY THE RIGHT QUESTION!!!!!

I believe when they were new they measured about 5 Ohms. They age, and the metallic portion corrodes away (or gets scratched thru) and the resistance climbs slowly up. Once they get over about 15 Ohms they are all but worthless.

I'm afraid your worst fears are correct. If you really read a high resistance then this one is dead. Don't feel too bad. By now, almost all of them are dead.

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Wow -- useful information. At 12 volts, that's 29 watts of heating power.

Is this 5-ohm spec something you determined yourself, or some spec that is buried in VW documentation?

I think btlmex also has new rear windows with the defroster grid, but from what I remember they are also expensive.

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" ..... I ain't no bandleader!!"

A great big OPEN circuit................Something about a foot in the circuit though wasn't there. How's Shag anyway?...........anyone following his antics lately? ( I dare not call them adventures , as I am not aware of what he's been doing with the geep )

Remove "YOURPANTIES" to reply MUADIB®

At 14.4 V it comes to more like 45 W, which is the number that I believe is listed in Without Guesswork.

For the record, I've don't recall ever measuring one as low as 5 Ohms, by the time I noticed the problem they had all increased somewhat. I have (had) one that measured 7-8 Ohms a few years ago. I wonder what it measures now...?

----------------------------------------------- Jim Adney snipped-for-privacy@vwtype3.org Madison, WI 53711 USA

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Oh, right. My newbie error: a 12v system usually runs hotter than that.

I'll need to check mine. Probably open by now.