# Rear defogger - does it actually work



## nonStopSwagger (May 7, 2018)

My 3's rear defroster/defogger, I've never seen it do anything. Is there a scenario I can follow to test if the thing is broken? Mist water onto the inside of the window, then turn it on etc?


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## MJJ (Aug 7, 2016)

Park outside overnight?

I believe the rear mirror heaters and the rear window defroster come on together, based on the glacially (pun intended) slow pace that frost thaws in those areas. NOT over-powerful.

Interestingly, the other morning I came out to a very frosty car, but the area around the front facing cameras was spotless.


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## Darrenf (Apr 5, 2016)

Works more quickly than any rear defroster I've ever seen. In the morning here when the rear is covered in ice, within a minute of turning it on it's just about all gone. Most impressive.


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## Nautilus (Oct 10, 2018)

Darrenf said:


> Works more quickly than any rear defroster I've ever seen. In the morning here when the rear is covered in ice, within a minute of turning it on it's just about all gone. Most impressive.


Agreed. It's just very hit or miss whether it will come on automatically when preconditioning the car. That said, if the back window is fogged or frosted, or even had light snow on it (@MJJ is right, just park it outside overnight, especially in NH), when you turn it on from inside the car, you will start to see the impact within a minute or two of driving.


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## Karl Sun (Sep 19, 2018)

You could easily test it using an IR temp sensor. 

NOTE: There may be some circuitry or programming that limits power to the rear glass heater depending on outside/ambient temp. That's how I would do it.


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## Bibs (Jun 9, 2018)

Agree with the above posts. After years of driving various cars through harsh winters all over the country, I've found that the Model 3 rear defroster works faster than most cars.

As for the wavy/distorted thing: yes, that is because of the embedded wires in the rear glass, but not because of any heat. The rear window is at a very low angle; when you look through such an acute angle, even small variations in the glass become apparent. Any window with defrosters would look the same if it were mounted at a similar angle.


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## SoFlaModel3 (Apr 15, 2017)

Parked outside overnight at a hotel recently and it cleared this up very quickly...


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## nonStopSwagger (May 7, 2018)

Thanks all for the suggestions. I'm going to park it outside tonight in the driveway. I'll try and take some video or photos in the morning if I get some frost/moisture on it. My test will consist of:

Unlock the car with the keycard (not the phone, don't want the car to sut off when I close the doors and am not inside)
set heat to 68 (manual, fan speed 1, no ac), turn on rear defroster. 
Exit the car, start recording video on a tripod
Overnight temps tonight will dip below freezing, no snow or rain forecast. I'll report back over the weekend.


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## Nautilus (Oct 10, 2018)

SoFlaModel3 said:


> Parked outside overnight at a hotel recently and it cleared this up very quickly...
> 
> View attachment 22295


Ah yes, I lived in Winter Park during the summer of '85. The only place I lived where I had to have a squeegee to get all the condensation off the windows each morning! It wasn't just the back window, but all the windows. Couldn't see a thing unless I squeegeed.


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## Long Ranger (Jun 1, 2018)

My poorly phrased original post on distortion was moved here:
https://teslaownersonline.com/posts/206640/

I'll try to be clearer here. My suggestion is to simply turn on the defroster at any time and look for distortion out the rear window. You don't need to start with a fogged window. On my car it's pretty obvious if the defroster is on just by looking in the rearview mirror. It takes several minutes, but with a clear window and the rear defrost running there is noticeable distortion in the laminated glass.


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## mswlogo (Oct 8, 2018)

Mine works great. It’s very fast. 

Sorry to ask a dumb question but are you hitting the rear defog button? I don’t believe any other scenario will turn it on automatically. Including Auto. Some cars do tie it to other modes. Like the defrost on some cars might turn the side mirrors and rear with it. As far as I know the Model 3 does not. I forget what the side mirrors come on with. Since the generally haven’t been an issue.


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## nonStopSwagger (May 7, 2018)

Tested it this morning, it does indeed work. I'd rate it as average compared to my f150 and XC90 for performance. No better, no worse. Temps were in the high 20's

Test subject. Light frost on the glass









Settings I used









After 5 minutes









After 10 minutes, all that's left is a little frost near the middle light in the glass.









Thanks all for indulging me. I almost never park outside, the only one time I tried to use the defroster previously I had a rear window covered in almost an inch of snow. At that time, it didn't seems to work, at least not in the 15 minutes I was in the car.


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## Nautilus (Oct 10, 2018)

@nonStopSwagger , if you happen to park outside on a night when there's a good heavy frost (the kind you need the ice scraper for), I think you'll find it works better. I'm not sure there was enough of a frost for the defroster to work with (if that makes sense). Regardless, at least you now know that it does indeed work.


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