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Keeping Model Y Window Defrost and battery management during winter

psuKinger

Member
Jul 3, 2020
90
89
Pennsylvania
tl/dr summary: This is my first Tesla (or EV for that matter). I know best-practice for maximizing range in the winter is to not heat the cabin excessively. Looking for settings that other Model Y owners are using that keep the front windshield (and possibly front windows too) defrosted WITHOUT warming the cabin up heavily... essentially, I'm looking to maximize range *AND* see out an unfrosted front windshield...


Longer version:
Winter has arrived in Pennsylvania... my first winter as an EV owner. My wife took the Tesla yesterday, and got some pretty hefty *range anxiety* as the day went along... we are trying to *learn fast* how best to drive/own these during the cold weather months.

I had the battery charge to 82% overnight, then this morning about an hour before I was going to leave I turned the charge on, and it ran at ~240V/32A for a little less than an hour... got in at right around 91%, and it drove real well on my way into work. Used just about as much battery to drive in (~7%) as it did during the summer months. So that was great to see!

But we are both still struggling with optimal settings to keep the window defrosted... I know all the official (and unofficial) Tesla advice says to NOT heat the cabin, but rather use the seat heaters, for warmth... and I kinda like it cold(er than most, at least), so I wasn't particularly concerned... but now Winter has arrived, and we are both finding it awfully hard to keep even a "reasonable portion" of the front windshield defrosted without having the temperature at *at least* 69 (if not 70) and the blower up to at least 7 (often 8+).

Temperature at 70 and blower at 8 works well... but the cabin is near-uncomfortably-warm for me (the warm-blooded one). I'm sure my wife is not too hot like this, but she would certainly agree that it's warmer than it *needs* to be for reasonable comfort and maximizing battery life.

Last night she found that turning the front vents on as well and then aiming them very far out-and-up seemed to have a couple positive affects:
1) pointed out-and-up seemed to help defrost the side windows
2) it made the blower less noisy (while still set to 8) without negatively affecting the front windshield defrost (much)

But the end result is still a warm/(very) comfortable cabin....

How is everyone else keeping their front windshield defrosted as we enter into winter? Any settings/tips to share?

Thanks in advance.
 

jcanoe

Active Member
Oct 2, 2020
1,754
1,732
Maryland
There are two things to consider; the first is defrosting the windshield, side windows and the rear glass. The second is how to keep the windows from fogging up. Usually the inside of the windshield will fog up, sometimes when conditions are right the outside of the windshield can fog up.

When you precondition the Tesla Model Y in cold weather the defroster will come on automatically. If the vehicle is parked inside a garage there may not be a need to defrost the windows but there it is. Once you start driving the humidity level in the cabin will increase due to your respiration, with two or more occupants the effect is multiplied. To minimize fogging of the windows do not turn on cabin air recirculation as this will cause the windows to fog up even faster. Run the HVAC in Auto at a temperature that you find comfortable, the AC will dehumidify the air in the cabin. 69F to 71F is where I usually have this set.

Keep inside surface of the windshield as clean as possible as any film or dirt on the glass surface seems to increase condensation and fogging. I prefer Invisible Glass cleaner applied to the inside of the windshield and then wiped dry using a clean microfiber cloth. You may have to repeat the cleaning with the Invisible Glass cleaner more than once. Once clean, the glass tends to stay clean for a long time and fogging is minimal and quickly dissipates when you warm up the glass surface. You may be able to minimize fogging of the inside of the windows if you apply a window treatment (I don't have one to recommend.)

Recently, for the first time, I experienced fogging of the side mirrors. I tried the front defroster.The front defroster has two settings when turned on; the first press of the front defroster screen button turns the icon blue (for AC defogging) and the second press of the front defroster screen button turns the icon to red on the Tesla information screen.

When the front defroster icon is illuminated red the front defroster operates the way Max Defrost worked in my previous vehicles; maximum temperature and maximum fan. There does not appear to be a way to turn down the fan speed or adjust the temperature as this turns off the front defroster function.

The rear defroster button turns on the heating wires in the hatch glass.Turning on either the front defroster or the rear defroster seems to activate the side mirror heaters.
 
Last edited:

Ldub22

Member
Mar 1, 2015
173
131
Kirkland, WA
I have found that "preconditioning" the car to the optimal temperature BEFORE I leave my office is by far the best. @jcanoe is exactly right: you need to get the humidity out of the car before you get in, carrying your show/wet/breathing/moist body into the car.

If you leave the car cold and somewhat moist, then the initial rush of all the moisture you bring in with you will be added to the load that is already in the car.

I think that you may be getting a little preoccupied with range anxiety as it relates to the HVAC. The amount of energy used to precondition your car and warm the battery is miniscule vs. the amount that it takes to motivate the car. If driving to work takes 7% of the battery, and 14% total, then even with vampiric loss in the cold, you could keep the car on max defrost all the time!

But you don't want to get hot. So, just run the HVAC for 10-15 minutes before you leave work. Car is your perfect temperature, and the octovalve can suck the moisture out before you even get in.

Beyond that: have driving slippers/shoes in the footwell and take a minute to shake snow off your boots. Take off your coat/hat/gloves/scarf. I've been doing that kind of stuff for decades as a skier, with and without a Tesla!
 

psuKinger

Member
Jul 3, 2020
90
89
Pennsylvania
Once you start driving the humidity level in the cabin will increase due to your respiration, with two or more occupants the effect is multiplied. To minimize fogging of the windows do not turn on cabin air recirculation as this will cause the windows to fog up even faster. Run the HVAC in Auto at a temperature that you find comfortable, the AC will dehumidify the air in the cabin. 69F to 71F is where I usually have this set.

Thank you!!

I'm kicking myself a bit, as some of that *should have* been obvious to me, but it wasn't...
1. I am referring to interrior humidity fogging and not frost on the exterior. You guessed correctly I was using those (mistakenly) interchangably.
2. I'm fairly certain I still have "recirculate air" set from the warm summer months, for efficiency... I am 99% sure this is my error that is causing me grief.
3. I will also switch to "auto temperature"; I liked manually controlling the breeze (force and direction) during the summer months, but with winter upon us I don't need that anymore.

I am confident your post is going to really help me out tonight and going forward. Thanks for taking the time with that.
 
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Big Earl

bnkwupt
Jul 12, 2017
5,199
9,376
Springfield, VA
Have you tried setting your temperature and running the system on automatic mode?

Forcing recirculating will definitely cause excessive humidity buildup.

Forcing a high fan speed with fresh air will use more energy than necessary to maintain comfort compared to a more moderate fan speed.
 

HarleyW

Member
Apr 14, 2020
46
36
Denver, CO
There are two things to consider; the first is defrosting the windshield, side windows and the rear glass. The second is how to keep the windows from fogging up. Usually the inside of the windshield will fog up, sometimes when conditions are right the outside of the windshield can fog up.

When you precondition the Tesla Model Y in cold weather the defroster will come on automatically. If the vehicle is parked inside a garage there may not be a need to defrost the windows but there it is. Once you start driving the humidity level in the cabin will increase due to your respiration, with two or more occupants the effect is multiplied. To minimize fogging of the windows do not turn on cabin air recirculation as this will cause the windows to fog up even faster. Run the HVAC in Auto at a temperature that you find comfortable, the AC will dehumidify the air in the cabin. 69F to 71F is where I usually have this set.

Keep inside surface of the windshield as clean as possible as any film or dirt on the glass surface seems to increase condensation and fogging. I prefer Invisible Glass cleaner applied to the inside of the windshield and then wiped dry using a clean microfiber cloth. You may have to repeat the cleaning with the Invisible Glass cleaner more than once. Once clean, the glass tends to stay clean for a long time and fogging is minimal and quickly dissipates when you warm up the glass surface. You may be able to minimize fogging of the inside of the windows if you apply a window treatment (I don't have one to recommend.)

Recently, for the first time, I experienced fogging of the side mirrors. I tried the front defroster.The front defroster has two settings when turned on; the first press of the front defroster screen button turns the icon blue (for AC defogging) and the second press of the front defroster screen button turns the icon to red on the Tesla information screen.

When the front defroster icon is illuminated red the front defroster operates the way Max Defrost worked in my previous vehicles; maximum temperature and maximum fan. There does not appear to be a way to turn down the fan speed or adjust the temperature as this turns off the front defroster function.

The rear defroster button turns on the heating wires in the hatch glass.Turning on either the front defroster or the rear defroster seems to activate the side mirror heaters.

Another thing to consider is as it is a heatpump it cannot do both heating and cooling at once. (I don't believe) And in a "normal" car when you turn on the defrost setting the AC compressor turns on to dry the air and then it goes thru the heater core to heat the air before it blows the dry warm air on the windsheild.

With only one system I can't see how it will both dry and heat the air to quickly defrost/defog the window. Mind you Tesla has done alot of things to make their vehicles more useful in a always warm climate. From the door handles and frameless windows that freeze and ice up to the considerable loss of range in cold temperatures. We have a model 3 at work here and everyone calls it the California car. It sits around alot more unused in the winter.
 
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pt19713

Member
Feb 5, 2020
861
1,037
Delaware
The Y uses little energy to heat the cabin, 350-500 watts. All the horror stories you hear are from the Tesla's that don't have a heat pump. Those heated filaments can take 2-4 kW.

My advice, don't worry about it too much in your Y. Keep the cabin heated as normal while you're driving, pre-condition whenever possible.

Also, 1 heated seat takes 100 watts. With 1 heated seat on, hvac on, etc my car is pulling around 1-1.1 kW (cameras and sensors for AP pull 250 watts). In perspective, cruising at 55mph on a flat road takes 13 kW, so the energy to heat the cabin and run everything is pretty minor in the whole scheme of things.
 

Big Earl

bnkwupt
Jul 12, 2017
5,199
9,376
Springfield, VA
Another thing to consider is as it is a heatpump it cannot do both heating and cooling at once. (I don't believe) And in a "normal" car when you turn on the defrost setting the AC compressor turns on to dry the air and then it goes thru the heater core to heat the air before it blows the dry warm air on the windsheild.

With only one system I can't see how it will both dry and heat the air to quickly defrost/defog the window. Mind you Tesla has done alot of things to make their vehicles more useful in a always warm climate. From the door handles and frameless windows that freeze and ice up to the considerable loss of range in cold temperatures. We have a model 3 at work here and everyone calls it the California car. It sits around alot more unused in the winter.

Yes, it absolutely can, as it has both an evaporator and a condenser within the cabin.

Check out this excellent three-part video series about how the Model Y HVAC system works. It’s brilliant.

part 1:

part 2:

part 3:
 
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pho35

Member
Aug 20, 2020
43
22
Texas
I think OP experience holds true for any car, when I used to own ICE cars, same would happen during cold days. I typically rolled the windows down for a few minutes to "reset" and it seem to help the rest of the way to get rid of cabin build-up.
 

Koolio46

Member
Aug 26, 2020
466
189
Boston, MA
The Y uses little energy to heat the cabin, 350-500 watts. All the horror stories you hear are from the Tesla's that don't have a heat pump. Those heated filaments can take 2-4 kW.

My advice, don't worry about it too much in your Y. Keep the cabin heated as normal while you're driving, pre-condition whenever possible.

Also, 1 heated seat takes 100 watts. With 1 heated seat on, hvac on, etc my car is pulling around 1-1.1 kW (cameras and sensors for AP pull 250 watts). In perspective, cruising at 55mph on a flat road takes 13 kW, so the energy to heat the cabin and run everything is pretty minor in the whole scheme of things.

Regarding heat pump energy use, Bjorn Nyland has a great video comparing his M3 to a new 2021 M3 with heat pump. He measured energy use of both cars to heat the cabin for 3 hours. The net: the 3 with heat pump only consumed 3% battery vs 10% for his 3 without the heat pump.

 
  • Informative
Reactions: srlawren

pt19713

Member
Feb 5, 2020
861
1,037
Delaware
Regarding heat pump energy use, Bjorn Nyland has a great video comparing his M3 to a new 2021 M3 with heat pump. He measured energy use of both cars to heat the cabin for 3 hours. The net: the 3 with heat pump only consumed 3% battery vs 10% for his 3 without the heat pump.

One thing to keep in mind is that the new Model 3 had both vents running. I guess they haven't gotten the software update to turn off the passenger side vent when no passenger is detected?

Bjorn is showing 700 watts to run the heat pump. I'm showing about 500 watts in the Y (with one vent closed). I'll test again when my wife and I take a drive and see if that goes from 500 to 700, although we aren't really going anywhere at the moment.
 

psuKinger

Member
Jul 3, 2020
90
89
Pennsylvania
Thanks guys. I'm a bit embarrassed by all this, but the first couple of replys here hit the nail on the head.

I needed to stop recirculating the moist air. Which I knew, but the thought just never occurred to me... running in "auto" has fixed all of this.

Additionally, the wife and I have gotten into better habits of "topping off" (from 80% to 90%, for example) 20-60 minutes before we leave in the morning, and getting the heat/defrost turned out 10-15 minutes before we go to get in the car when we aren't at home. These tricks have really helped with battery range. Thanks for the info and tips!!
 

skidmarc

Member
Nov 13, 2020
55
44
Atlanta
I see this so often, especially in Uber rides and friends' cars--not a Tesla issue. In the winter, using AC is critical to remove the moisture from inside the cabin. I see people turn the fresh air fan on high bringing in super cold air that mixes with the warm moist air inside the cabin and causes the fogging quickly. Then they turn all ventilation OFF for fear of being cold. Using the auto setting to keep the interior dehumidified, even in the winter is critical. Then, when defrosting is needed, use that setting to warm the glass. Most cars automatically turn the AC on when using front defrost now, anyway. We should all learn! I don't have my MY, yet, pick up next weekend. One thing I know for sure, i am going to drive and enjoy the car and not sweat all of these small, incremental range issues. Be comfortable. Love the technology and enjoy the ride!
 

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