Windshield Defogging issues

[ftnguyen1]

I've had an issue several times now where using the defog button increases the fog build up on my windshield significantly to the point that i can't see out the front while driving. I'll turn defog on at the slightest hint of fog buildup to try to preempt it but then this happens and driving with my head out the window or trying to pull over till it clears up. Once it builds up it still takes a couple mins to clear with defog running and all my windows down to help. Brought my car into service a couple months ago and they said my HVAC is working correctly and to make sure i use defog(cooling) and not defrost(heated) and try to video record it if it happens.

Took my car into service today along with the video and they said the same thing, that my HVAC was tested and working correctly but they saw from the video i was using the defog(cooling) setting and said that i need to use the defrost (heated) setting.

I know you're generally supposed to use cold, dry, a/c air to defog the inside of the windshield the quickest and i have never had this issue in my previous 2020 Model 3 or other cars.

Has anyone ran into this issue or have any suggestions? I'm also located in SoCal so the weather isnt too extreme and this generally only happens on cold nights.

 

[jcanoe]

I've had an issue several times now where using the defog button increases the fog build up on my windshield significantly to the point that i can't see out the front while driving. I'll turn defog on at the slightest hint of fog buildup to try to preempt it but then this happens and driving with my head out the window or trying to pull over till it clears up. Once it builds up it still takes a couple mins to clear with defog running and all my windows down to help. Brought my car into service a couple months ago and they said my HVAC is working correctly and to make sure i use defog(cooling) and not defrost(heated) and try to video record it if it happens.

Took my car into service today along with the video and they said the same thing, that my HVAC was tested and working correctly but they saw from the video i was using the defog(cooling) setting and said that i need to use the defrost (heated) setting.

I know you're generally supposed to use cold, dry, a/c air to defog the inside of the windshield the quickest and i have never had this issue in my previous 2020 Model 3 or other cars.

Has anyone ran into this issue or have any suggestions? I'm also located in SoCal so the weather isnt too extreme and this generally only happens on cold nights.

Set the Climate Control to Auto; set your preferred temperature between 68F and 72F; set the fan speed control to Medium or High (in the Auto setting the fan speed control functions as a speed limiter.) Turn off Recirculate Cabin Air if windshield fogging is an issue. When set to defogger the windshield defogger/defroster icon will be blue. When set to maximum defrost mode the icon will be red.

California has been experiencing heavy rain; check for any water leakage under the dashboard that may have soaked the carpet.

A full load of passengers will add to the cabin humidity through respiration.

Keep the inside glass surfaces clean; I recommend Invisible Glass spray (not the aerosol can.) Use a clean microfiber cloth, fold over a new section of the microfiber cloth for each half of the windshield. The windshield will resist fogging if the inside glass is squeaky clean.

 

[ftnguyen1]

I think it's happened with and without my climate control on auto which usually sits around those temps if it's on. Has happened while I'm by myself and of course when there's passengers. I'm actually a bit hesitant to use the Defog button while driving since this can occur and end up just rolling down my windows sometimes.

Here's the video i was able to record recently that i sent to Tesla Service.

 

[jcanoe]

I think it's happened with and without my climate control on auto which usually sits around those temps if it's on. Has happened while I'm by myself and of course when there's passengers. I'm actually a bit hesitant to use the Defog button while driving since this can occur and end up just rolling down my windows sometimes.

Here's the video i was able to record recently that i sent to Tesla Service.

At the end of the clip the fogged windshield appeared to be clearing. This is approximately 40 seconds after you turn on the windshield defogger.

If you make another video you might want to display the Climate Control settings while recording.

 

[ftnguyen1]

At the end of the clip the fogged windshield appeared to be clearing. This is approximately 40 seconds after you turn on the windshield defogger.

If you make another video you might want to display the Climate Control settings while recording.

Yea, it ends up clearing but its a bit dangerous driving with limited visibility at night like that. At the beginning of the video you can see that visibility is still good until after i turn on defog which then makes it significantly worse.

I'm assuming turning on defog shouldn't make it worse than it is and should slowly clear it out so i can see while driving. Alternatively, i've just been opening my windows for now since i know thats not going cause my windshield to fog completely up while driving, not exactly the ideal solution though.

 

[jcanoe]

Yea, it ends up clearing but its a bit dangerous driving with limited visibility at night like that. At the beginning of the video you can see that visibility is still good until after i turn on defog which then makes it significantly worse.

I'm assuming turning on defog shouldn't make it worse than it is and should slowly clear it out so i can see while driving. Alternatively, i've just been opening my windows for now since i know thats not going cause my windshield to fog completely up while driving, not exactly the ideal solution though.

You could turn on the windshield defogger before you start driving. That is what I usually do, then turn it off after several minutes.

 

[Brian-MS90D]

You're driving with your HVAC system off. You also do not have it set to auto, which puts all of the "responsibility" for knowing what your settings should be for your environment on you. Plus, you're asking for peak effective performance when the HVAC system is just spooling up and getting started, but no HVAC system can respond instantly like that when being first turned on.

Make life easy. Set your HVAC to Auto for your desired temperature and let the car do the rest. Keep it on all the time.

Then, if during the course of driving you start to get some fogging (maybe all your occupants start laughing at once, for example) you tap the defrost button until it clears up, while in Auto. The only time I "worry" about whether the defrost should be blue or red is when I need to clear snow or ice off the front windshield and I will force it into red defrost.

 

[ftnguyen1]

You're driving with your HVAC system off. You also do not have it set to auto, which puts all of the "responsibility" for knowing what your settings should be for your environment on you. Plus, you're asking for peak effective performance when the HVAC system is just spooling up and getting started, but no HVAC system can respond instantly like that when being first turned on.

Make life easy. Set your HVAC to Auto for your desired temperature and let the car do the rest. Keep it on all the time.

Then, if during the course of driving you start to get some fogging (maybe all your occupants start laughing at once, for example) you tap the defrost button until it clears up, while in Auto. The only time I "worry" about whether the defrost should be blue or red is when I need to clear snow or ice off the front windshield and I will force it into red defrost.

Running HVAC on auto all the time seems like a huge waste of energy in when i live in socal. Never had to do that with my other Teslas and no one i know with a Tesla (there's quite a few) has needed to do that around here.

I dont expect it to clear out instantly either, as mentioned, the issue im having is that turning it on makes it fog up completely blind instead of slowly clearing it out. As im turning defrost on to prevent the slight fog from getting worse, its a bit annoying and dangerous that it makes it significantly worse. I've also had the same issue happen with HVAC on auto then pressing defrost to clear up some slight fog.

FWIW, i spoke with a Tesla service advisor that also didnt know the difference between Defog(blue)/Defrost (red) and when to use it. A technician was nearby so he pulled him over to answer the question and the tech said that they both function the same besides temp and to just use Defrost(red) for everything.

 

[jcanoe]

Running HVAC on auto all the time seems like a huge waste of energy in when i live in socal. Never had to do that with my other Teslas and no one i know with a Tesla (there's quite a few) has needed to do that around here.

I dont expect it to clear out instantly either, as mentioned, the issue im having is that turning it on makes it fog up completely blind instead of slowly clearing it out. As im turning defrost on to prevent the slight fog from getting worse, its a bit annoying and dangerous that it makes it significantly worse. I've also had the same issue happen with HVAC on auto then pressing defrost to clear up some slight fog.

FWIW, i spoke with a Tesla service advisor that also didnt know the difference between Defog(blue)/Defrost (red) and when to use it. A technician was nearby so he pulled him over to answer the question and the tech said that they both function the same besides temp and to just use Defrost(red) for everything.

The Defrost setting uses more energy than needed to defog the windshield unless there is snow or ice.

Since you don't use the Climate Control full time have you tried cracking open one of the windows? Just sitting in the Tesla Model Y with the Climate Control turned off, your exhalations will quickly fog up the windshield.

 

[Brian-MS90D]

Running HVAC on auto all the time seems like a huge waste of energy in when i live in socal. Never had to do that with my other Teslas and no one i know with a Tesla (there's quite a few) has needed to do that around here.

I dont expect it to clear out instantly either, as mentioned, the issue im having is that turning it on makes it fog up completely blind instead of slowly clearing it out. As im turning defrost on to prevent the slight fog from getting worse, its a bit annoying and dangerous that it makes it significantly worse. I've also had the same issue happen with HVAC on auto then pressing defrost to clear up some slight fog.

FWIW, i spoke with a Tesla service advisor that also didnt know the difference between Defog(blue)/Defrost (red) and when to use it. A technician was nearby so he pulled him over to answer the question and the tech said that they both function the same besides temp and to just use Defrost(red) for everything.

In your easy climate the HVAC ran constantly on auto will use very, very little energy. You're probably using FAR more energy in your attempt to be miserly and then needing to BLAST defrost (of either type) for a short period until your igloo you've created fogs up again and then BLAST defrost again.

 

[woolymammoth17]

It's happening specifically because you're leaving it off and the system is activating for the first minute and blowing humid air onto the windshield. Don't run with climate off.

 

[coleman567]

It's happening specifically because you're leaving it off and the system is activating for the first minute and blowing humid air onto the windshield. Don't run with climate off.

THIS!!!

 

[Raafsail]

Hi guys, i Lelia’s in Portugal and the same thing happens in my model Y. Generally only in rainy days. I’ve always have my ventilation on AUTO mode. When i go from one place to another and make a stopover for a coffee there is a fan working when I leave the car ( Tesla service told me that it is a dehumidifier system working) the fact is that when a few minutes later I came back to the road screen is clear and after 5 minutes it starts fogging to the point I can’t see anything. If in look at the AC messages it is written autodefoogging
I really do not know how to solve this issue. Open a ticket on the app - waiting for an answer

 

[Big Earl]

I've had an issue several times now where using the defog button increases the fog build up on my windshield significantly to the point that i can't see out the front while driving. I'll turn defog on at the slightest hint of fog buildup to try to preempt it but then this happens and driving with my head out the window or trying to pull over till it clears up. Once it builds up it still takes a couple mins to clear with defog running and all my windows down to help. Brought my car into service a couple months ago and they said my HVAC is working correctly and to make sure i use defog(cooling) and not defrost(heated) and try to video record it if it happens.

Took my car into service today along with the video and they said the same thing, that my HVAC was tested and working correctly but they saw from the video i was using the defog(cooling) setting and said that i need to use the defrost (heated) setting.

I know you're generally supposed to use cold, dry, a/c air to defog the inside of the windshield the quickest and i have never had this issue in my previous 2020 Model 3 or other cars.

Has anyone ran into this issue or have any suggestions? I'm also located in SoCal so the weather isnt too extreme and this generally only happens on cold nights.

It takes time for the system to be able to begin heating and dehumidifying to remove fog from the windshield. If you have the system off and only turn it on once fog starts to form, you’re doing it wrong. Keep the system in auto to prevent fog from building up in the first place. You should only need to use the defog (windshield shaped icon) in extreme conditions.

 

[teca01]

I thought that the air is dehumidified by AC (cooling) in defog mode no matter what temperature setting is. Heating cannot remove moisture.

 

[Big Earl]

I thought that the air is dehumidified by AC (cooling) in defog mode no matter what temperature setting is. Heating cannot remove moisture.

That is correct, however, it takes a minute or two for the system to ramp up and actually do it. In the interim, the fan blowing air on the windshield can make the fog worse. The red defogging (tap the button twice) button typically performs the best (again, after a brief delay) because heated air results in lowered relative humidity and increased dew point. So while heat doesn’t remove moisture, it does make it less likely to condense.

 

[jcanoe]

The Tesla Model Y's Climate Control system with the heat pump is able to warm the air going to the windshield and cabin interior via the cabin heat exchanger, while simultaneously cooling, dehumidifying the air at the same time via the AC evaporator. This seems counter intuitive, inefficient as the warming and cooling processes would cancel each other but it works to quickly defog the windshield, other windows. ICE vehicles also can heat the cabin air while running the AC once the engine, engine coolant is sufficiently warmed.

 

[Ratm68]

i came here searching because of the same issue thinking that i'm doing something wrong (and maybe i am). a bunch of people blaming user error seems silly to me. Regardless of auto climate or not, when a user needs to defog, the one thing the car can't do, is make the situation worse (even if temporary). I think tesla should enables climate when rain is detected if this is such a requirement to ensure the windshield doesn't fog up unexpectedly when you hit that defog button.

 

[jkdman123]

I haven't experienced this problem yet, but to all those claiming that it's somewhat normal behavior for an HVAC system, I call shenanigans. I have NEVER driven a car in my life, owned, rented, borrowed, etc. where the defogger didn't start clearing the fog from the inside of the windshield within *seconds*. It may take a min or so to completely clear it, but it never got *worse* the moment the defogger was turned on. I'm not saying I've driven every car in the world, but I would say what the OP is experiencing, if the HVAC is indeed working as designed, is not standard across the automotive industry.

 

[Big Earl]

Defogging the windshield requires a few things: heat, dry air, and air velocity. Once an ICE car is warmed up, there is instant heat available for defogging the windshield. If you're running your system in manual mode with A/C off, it's going to take a minute for the heat pump system to start delivering dry heat.

It's important to mention that the defog button has two modes: BLUE icon (one tap) is maximum cooling to the windshield. RED icon (two taps) is maximum heating to the windshield. Heating is much more effective than cooling, but it takes a moment for the heat to really get going.

If you're using the system in automatic mode, the system will already be dehumidifying and conditioning the air, almost always preventing fogging in the first place.