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-   -   Rear defogger not working (https://www.team-bhp.com/forum/technical-stuff/15673-rear-defogger-not-working.html)

This monsoon I discovered that my rear defogger does not work.
The car is a Honda City and the defogger is on the rear windscreen.

It is confirmed that there is electrical supply to both the leads on either side.
But still the damn thing will not warm up.

After some head scratching, I remembered that I had put sun screen film on my windows, prior to my long Kerala trip, this summer.

Could window film be the cause of the defogger going bonk?

Venkat

Your installer probably cut the heater strip somewhere during the installation of sun film. Thats the problem. A lot of inexperienced installers end up doing this. Solution? well I think you need to find the cut and re-join it. With what(?) may be a question someone else can help you with.
For fixing it you have to remove the sun film and that may lead to more breakages in the heater strip!!!

Hi Venkat:

Sunfilm by itself is an insulator. So is the glass on which the defogger heating element is embedded. And sunfilm adhesives are not strong enough to pull the demister apart. So the sunfilm is probably not the culprit.

But I agree with jyobeb. Your sunfilm installer probably nicked the heater strip while installing the sun film.
For even troubleshooting it, you will have to delicately remove the sunfilm without any more breakages in the heating element.

Use a simple multimeter to measure the resistance of the defogger from terminal to terminal. If the multimeter does not show open circuit, the demister switch or wiring is suspect.

The rear demister grid would stop working if there is a break in the grid lines somewhere or one of the electrical connectors on the glass has broken off.

Use the multimeter or a test lamp to check for voltage at between the terminals and ground with the demister switched on. One side should show 12 volts to ground.

If there is a break in the grid it can be repaired by joining the break back together
using Loctite DK1 Demister Repair Kit
or FrostFighter 2100 Defroster repair kit


The trick is in determining where the break is.
This can be done by grounding one side of the testlamp and puncturing the grid at different places.
The break is where the light no longer lights up.

Ram, 48, Pune & Mumbai

great and while we are at it, could someone suggest me how to speed up the de-mister on my xeta..! It takes more than 5 min in the rains to heat up the glass, or to get faster response I just have to blast the AC..!

Hey thanks guys...

I did visually check the entire grid, from outside and from inside. I could not visually locate any breakages in the grid.

Being the Ham Radio operator that I am, I should have thought about using the multimeter to determine connectivity or lack thereof.

My local electrician used the lamp test by connecting lamp leads to either terminal and it lighted up, proving that the dash switch and wires were OK.

While I will still see if there is a break in the grid, I was wondering if certain films were having a metal coating that could be reducing the resistance and thus leading to lack of heat generation.

Thanks guys for the response so far.

Venkat

Even i am facing the same problem on my OHC Vtec.. the rear windscreen defoster dosenot work!!

Thanks for giving information about the kit

This group has got many guru's.

I am hoping to fix this defogger problem and am now equipped with my multimeter. With that, I can measure the continuity across the rear windscreen. As well as the resistance.

The question that arises is that, what should be the measured resistance, in order to know if the defogger is working fine or not?

Venkat

First thing comes to mind is as follows:
Find out which end of the defogger is connected to ground.



Hope this helps. Do keep us informed.
:)
Ram.

reduced resistance should have resulted in "more" heat in fact. If there was a metal coating, it would cause a short circuit which could have blown up your wiring or a fuse (unless there is current limiter in the defogger circuit). So there are more chances of having an open rather than a short. Moreover, if sunfilms created any shorts then it would have been a well know problem (which I believe is not the case:))

http://autorepair.about.com/cs/doity.../aa112302a.htm

see if this link helps. page 3 should help i suppose as all other checks done by u seem to work.

do let us know when u have rectified the problem.

Guys,

Thanks a lot for all the helpful hints. Ram's coding structure was really nice as well as the link to About.com.

While I will do the preliminery tests this weekend, a long solution needing refixing the grid may require me to remove the sun film first. And very carefully under my supervision this time.

What ever happens, be assured that I do not leave behind hanging threads.

Venkat

Over the long weekend, I could finally take the time to go down to my car with my multimeter.

On the HOnda car, where the defogger does not work, it registered a resistence of about 1.5K ohms.

On the Wagon R, where it works fine, it registered continuity with no resistence.

So definitely there is a break somewhere.

Next step, take the rear film down. Bad job.

But now that the monsoons are getting over, should I just leave it on to do the job that it was intended for?

Who says procastination does not have its rewards?

Venkat

yeah a noob query does using the rear defogger spoil the film,my uncle has a palio and the film on the rear pane is all crumpled up like when we move something hot over plastic

Yogi....I think this would happen defnitely. In fact thinking about it, it is not a good idea to put film on the rear window at all if there is a defogger.

1. If the film is applied properly, and the defogger is still working, then the film heats up and wrinkles up leaving it messy and useless.
2. If the film is not fixed properly, the defogger is gone for a toss.

What do the resident guru's opine?

Venkat

Venkat, I concur with you.
Maybe the film is contraindicated for backlights that have demister wires.

Applying dyed polyester film on glass is something I've seen only in India, where many places and climates do not require the backlight demister.

The old Fiats and Ambassadors and even the older Maruti 800s and Maruti 1000s came without demisters, so it was OK to have the polyester sunfilm on the glass.

Higher end saloons often have tinted glass anyway so don't require tinted film. And VIP limousines with near-black and metallized one-way glass are custom jobs anyway, where a specialist can do the needful scientifically.

Ram