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Crazy bad fogging of windshield in humid weather

Petrlol

Member
Oct 16, 2018
399
537
Ohio
I see it's a newer car (June 2020) The off-gassing is horrible for the first 6 - 12 months. Be sure the inside of the glass is super clean every few weeks. Set the vent to windshield. 72-ish, and fan speed 8 has always taken care of it in a minute or two for me. After wards I can push it back to 68 auto - depending on the length of the drive I may have to do that a few times.
 
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TLLMRRJ

Active Member
Dec 19, 2019
1,735
1,685
Houston
Here in Houston, I am getting that crazy fogging sometimes as well since it's August.

It's not on the inside, so it's not offgassing. You pretty much have to use the wipers when it's really heavy fogging. The defrost setting of the climate control isn't going to clear the moisture on the windshield anytime soon.
 
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hcdavis3

HCD3
Mar 3, 2019
1,831
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Here in Houston, I am getting that crazy fogging sometimes as well since it's August.

It's not on the inside, so it's not offgassing. You pretty much have to use the wipers when it's really heavy fogging. The defrost setting of the climate control isn't going to clear the moisture on the windshield anytime soon.
That’s exactly my case.
 

XLR82XS

D M C
Jul 26, 2019
3,094
1,726
SWFL | Vegas
You want air conditioned air to blow on the windshield. Your fogging issue is because of water vapor. Air conditioned air has no water vapor.
It's not on the inside, so it's not offgassing. You pretty much have to use the wipers when it's really heavy fogging. The defrost setting of the climate control isn't going to clear the moisture on the windshield anytime soon.
Defrost button will clear inside windshield moisture with the A/C compressor activated. Wipers will not so anything to clear the interior glass.
 
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hcdavis3

HCD3
Mar 3, 2019
1,831
1,067
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You want air conditioned air to blow on the windshield. Your fogging issue is because of water vapor. Air conditioned air has no water vapor.
Thanks Gasarski. It’s gonna be hot and humid here again tomorrow. I’ll try this. The fogging is on the outside of the windshield.
 

theothertom

Member
May 9, 2020
263
157
South Carolina
Fogging is on the outside of the windshield.
Most people would use the term "fogging" for moisture condensation on the inside of the windshield. If it's on the outside, it's because the humidity is high and the windshield is cool. I assume your windshield wipers would remove it? Edit: This happens to me a lot when I park outside.
 

drdumont

Member
Nov 22, 2019
266
281
North Texas
Fogging is on the outside of the windshield.

OK. Two points here.
1) If it is really humid inside the car (maybe you just came in from the rain? Breathing hard?), the humidity will build up and condense on a cooler surface in the car. Like the windows or windshield. (Google Dewpoint). Turn on the A/C, set at some reasonable setting like 73 or 74. Turn on RECIRCULATE. Now the air will recirculate over the coils, the moisture will condense on the coils and you will have "dehumidified" or dryer air. Turning on the interior dehumidifier pretty much does that plus directs the air to the windshield. In an ICEV, you used to be able to run the temp way up and still have the compressor running. I think the energy saving brains in the Tesla might cut off the compressor at higher temps.

(Note - I left the top down in a rented Mustang in Florida years ago. Drenched everyting, including fabric seat covers. Left the car running with A/C on Recirc set about 80 degrees for about 4 hours. With the top and windows closed of course. After that, the inside of the car was as dry as a skeleton's ass. Budget never knew what had happened).

2) If the fogging is on the outside of the windshield, that means you are likely blowing cold air on the windshield, cooling the glass below the dewpoint of the outside air and the water condenses on the outside. As long as the glass is cooler than the air outside, the water will reappear. Don't blow cold air on the windshield. A little warmer air helps but will take awhile to transfer the heat to the outside of the windshield. Thermodynamics and conservation of energy and all that.

And of course, if you think you have the defroster on, make sure you are using the right "button". I believe the rightmost is the "defogger" or heat coils for the rear window, and the left one is for the windshield. You might have to RTFM, my memory got up and went a long time ago.

Class dismissed.
 

hcdavis3

HCD3
Mar 3, 2019
1,831
1,067
02571
OK. Two points here.
1) If it is really humid inside the car (maybe you just came in from the rain? Breathing hard?), the humidity will build up and condense on a cooler surface in the car. Like the windows or windshield. (Google Dewpoint). Turn on the A/C, set at some reasonable setting like 73 or 74. Turn on RECIRCULATE. Now the air will recirculate over the coils, the moisture will condense on the coils and you will have "dehumidified" or dryer air. Turning on the interior dehumidifier pretty much does that plus directs the air to the windshield. In an ICEV, you used to be able to run the temp way up and still have the compressor running. I think the energy saving brains in the Tesla might cut off the compressor at higher temps.

(Note - I left the top down in a rented Mustang in Florida years ago. Drenched everyting, including fabric seat covers. Left the car running with A/C on Recirc set about 80 degrees for about 4 hours. With the top and windows closed of course. After that, the inside of the car was as dry as a skeleton's ass. Budget never knew what had happened).

2) If the fogging is on the outside of the windshield, that means you are likely blowing cold air on the windshield, cooling the glass below the dewpoint of the outside air and the water condenses on the outside. As long as the glass is cooler than the air outside, the water will reappear. Don't blow cold air on the windshield. A little warmer air helps but will take awhile to transfer the heat to the outside of the windshield. Thermodynamics and conservation of energy and all that.

And of course, if you think you have the defroster on, make sure you are using the right "button". I believe the rightmost is the "defogger" or heat coils for the rear window, and the left one is for the windshield. You might have to RTFM, my memory got up and went a long time ago.

Class dismissed.
Thanks. I have the hvac set to blow air from the vent, not toward the windshield. It appears that the air leaks toward the windshield on the right side.
 

AxlxA

Member
Jun 23, 2020
478
326
Bay Area
This kind of condensation on the exterior windshield happened on my old car every morning. 36F temp car sat outside all night, started driving and it'd blur up. I would warm the car and warm up the windshield and it usually resolves in 5 minutes.
 

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