How the Model Y heat pump works, its various modes and how it heats the battery:
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Discussion of A/C use in cold weather
- Thread starter TimothyHW3
- Start date
iwannam3
Active Member
In a fossil car the AC comes on in defrost mode for 2 reasons. to dehumidify and to exercise the AC compressor. In the early days of AC the seals would dry up and leak freon if they weren't spun and oiled by operating frequently. I assume modern seals are better, but the design may linger.
In a world where we have very advanced users (like many of you/us here on this forum), and very novice/timid users, companies are increasingly pressured to cover their butts and do what is safest for the masses. They still give you the option to turn off the A/C if you insist, but they default it to on likely for a mixture of simplicity and safety.
Safety? Yes, safety. About a year ago I was driving home at night on a cool night (Southern California cool, so maybe 9.5c). Like many of you, I had just my heat on, no A/C. I was driving about 75 MPH on the highway. Occasionally the corners of my windshield would slowly start to fog up, and I would turn on the A/C for a few minutes to dehumidify the interior. No problem. I had done it like this for weeks and had done it like this in ICE cars for my whole life. Normal night until all of a sudden about 75% of my windshield fogged up very quickly (in maybe 3 seconds) leaving me with an oval-shaped window of clarity in the center. In a moment of quick-thinking, I hit the defrost button on the screen. HUGE MISTAKE. The sudden rush of warm (and humid) air from the defrost vents completely fogged up the glass to where I had no visibility at all except for some distant red blobs that I knew to be taillights. Side windows were mostly fogged too, but I was able to look out the side and see I was still in my lane.
thankfully the defroster ultimately did its thing, but I still had no visibility at all for about 8 seconds. Then over the next 8 seconds or so the windshield completely cleared. I don't know the special set of circumstances that led to the sudden fogging (barometric pressure, temp, humidity just right?), but it's something that I'd rather not experience again. I still manually run heat only on cool days/nights, but if the windshield STARTS to fog up even a little, I let the car do its "auto" thing and keep the windows clear.
Safety? Yes, safety. About a year ago I was driving home at night on a cool night (Southern California cool, so maybe 9.5c). Like many of you, I had just my heat on, no A/C. I was driving about 75 MPH on the highway. Occasionally the corners of my windshield would slowly start to fog up, and I would turn on the A/C for a few minutes to dehumidify the interior. No problem. I had done it like this for weeks and had done it like this in ICE cars for my whole life. Normal night until all of a sudden about 75% of my windshield fogged up very quickly (in maybe 3 seconds) leaving me with an oval-shaped window of clarity in the center. In a moment of quick-thinking, I hit the defrost button on the screen. HUGE MISTAKE. The sudden rush of warm (and humid) air from the defrost vents completely fogged up the glass to where I had no visibility at all except for some distant red blobs that I knew to be taillights. Side windows were mostly fogged too, but I was able to look out the side and see I was still in my lane.
thankfully the defroster ultimately did its thing, but I still had no visibility at all for about 8 seconds. Then over the next 8 seconds or so the windshield completely cleared. I don't know the special set of circumstances that led to the sudden fogging (barometric pressure, temp, humidity just right?), but it's something that I'd rather not experience again. I still manually run heat only on cool days/nights, but if the windshield STARTS to fog up even a little, I let the car do its "auto" thing and keep the windows clear.
Agreed on security. I always prefer to have control though. On ICE cars AC would rob power so I would turn it off when I needed all the power. It was especially true on a turbo car.
On a Tesla it doesn't cause any power loss and honestly, the battery consumption isn't significant enough from just that to turn it off and be less comfortable.
On a Tesla it doesn't cause any power loss and honestly, the battery consumption isn't significant enough from just that to turn it off and be less comfortable.
Not sure what cars you had, but both of my last 2 cars would shut off the AC automatically when you hit the gas hard. The AC light would stay on, but you could feel the vent air warming up. Maybe only in certain driving modes like "sport" perhaps on newer cars though.
What are you talking about, I am talking about the AC setting in the car (you are confusing AC with HVAC...). Maybe see the video next time first...
I saw the video, before you posted it... no need to be aggressive about it. I'm saying that in the new Model 3 that he's testing, there should be a heat pump. Tesla have added it to the new 3's. Since it's cold outside, the heat pump should be in heat generation mode. Since it's the saame device that generates heat and cold (AC), it cannot be in AC mode at the same time. Thus the AC button should not be on.
Now, many ICE cars will let you turn off AC but they will silently turn it on when you use the defrost settings... so we can't always trust the AC light/button/etc to really show what's going on.
Separately, I'm wondering how such a heat pump system is able to remove the humidity from the air while heating. I believe I've found the answer on the internet: it should be alternating between modes. I'm just not sure... I'd like to understand that's all.
Now, many ICE cars will let you turn off AC but they will silently turn it on when you use the defrost settings... so we can't always trust the AC light/button/etc to really show what's going on.
Separately, I'm wondering how such a heat pump system is able to remove the humidity from the air while heating. I believe I've found the answer on the internet: it should be alternating between modes. I'm just not sure... I'd like to understand that's all.
Timothy, the heat pump IS the AC... It just can't do both at the same time... in fact I wonder how such a system can remove humidity in the air if it's in heating mode...
Yes, it can. It has both an evaporator and a condenser in the cabin. Check out the videos I linked in post #21.
I posted this on the 2021 vs 2020 thread, but will post it here again since this is now its own topic. Bjorn tested his car against a 2021. Heat pump 3x more efficient, at least while sitting still just to keep the cabin warm.
SageBrush
REJECT Fascism
This discussion strikes me as context dependent.
E.g., I live in a high desert climate. Winters days can get cold but the air is typically dry. If my car cabin is too humid (aka foggy windows) then I think my best conditioning would be a mixture of heating and ventilation. The best might be ventilation before I use the car, then ongoing heat pump use.
I know this:
In the winter I avoid bringing hot beverages into the car, and I try to keep snow out of the cabin. I find cabin air temperature in the 15 - 20C range along with a heated seat to be comfortable.
Fernand
Active Member
Anybody figured out a voice command to defog the windshield?
If I say "defrost windshield" it does, but also turns the heat all the way up.
Saying "defog the windshield" doesn't compute.
.
If I say "defrost windshield" it does, but also turns the heat all the way up.
Saying "defog the windshield" doesn't compute.
.
Bjorn's newest video shows that the Model 3 with a heat pump still uses the stators to heat the battery:
But it also uses the heat from the battery/drive units to keep the car warm inside.
Indeed it does. But there are a few variants of these cars with different batteries, let's see more tests so that we can conclude. AND! 24:13 They are not pulling 7.5-8kW like before, but just 6kW. Not sure the heat pump is helping as he mentions, maybe it is just for the cabin. Interesting to test too.
Really? I don't see how he can find out just from smt data...
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Really? Did you bother to watch the video? For example when he turns the heat on the heat pump activates and starts putting cooled coolant into the battery pack, because it is extracting the heat. Same happens while driving the pack gets cooled as it extracts heat. (Which doesn't happen with the older Model 3 without a heat pump.)
He even showed that that causes regen limits as well as slower charging if you don't navigate to a Supercharger because the battery pack is too cold...
android04
Active Member
In Nebraska in winter, I need to keep the A/C on (usually just have it in Auto) because my car windshield fogs up really quickly. Going into my 3rd winter with my Model 3. I am a little bit cold-blooded and many times I prefer not to even turn on the HVAC on my 25 minute commute to work. But I have no choice most of the time because of my windshield fogging up. I've experimented with different settings to try and get higher efficiency in the winter, and I even installed a physical switch to turn off the cabin heater. I tried turning off cabin heater and just circulating outside air with varying fan speeds. That sometimes works, but not always and I sometimes have to quickly enable AC again before my windshield fogs up and I can't see.
I actually did, and this part didn't make any sense. Especially in negative degrees temperature and the car being stationary the temperatures drop like crazy - it didn't "immeditaly" start doing the heating either. Plus I don't see why Tesla would let the car cool at 20C when it is freezing outside.
There might be SOME part of that extra heat being scavanged, but I doubt this is a significant amount.
Wait, are you talking about the "A/C" and then meaning the HVAC system as a whole. Or the AC part of the HVAC system? Because two separate things. I highly doubt that turning AC (AC icon) in addition to having the HVAC on will have anything to do with the windshields - if anything it will be the PTC...
android04
Active Member
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