Interesting behavior of heated seats

[StealthP3D]

Conditions:

28 degrees F
Car parked after 22 mile drive. No usage of heated seats.
Car sits 3 hours.
Open front door turn climate control on manual heat, A/C defrost on, rear window defroster on.
Exit car and close door.
Realize climate control turned off.
Use phone app to set temperature to 70F (the car was covered in a thin layer of ice/snow and inside windows were fogged).
Leave for 7-8 minutes.
Return to a warm car cleared of snow/ice and fog (except for the rear window, the defroster shut off when I exited the car).
Open passenger door, lean on seat surface and realize heated seats had been activated.
Looked at the display - it still showed all heated seat off.

What gives? Does the climate control turn on the heated seats automatically when there is nothing on them? The seats were definitely very warm, the heat could not have come from the vents. The heated seats were definitely showing "off" and were definitely "off" before the above sequence of events.

 

[drj3]

My car seems to use the seat heater when I preheat (at least for the driver's seat, I have not checked the others). I love being able to get into a nice warm car and seat when it's cold out. It does not seem to matter if I had the seat on for the prior trip or not.

 

[StealthP3D]

My car seems to use the seat heater when I preheat (at least for the driver's seat, I have not checked the others). I love being able to get into a nice warm car and seat when it's cold out. It does not seem to matter if I had the seat on for the prior trip or not.

Well, if the climate control is turning on the seat heaters when I pre-heat the cabin, that's a good thing. But it's not documented in the Owner's Manual and this is the first time I've noticed the seats getting warm on their own accord (and without the center display indicating the seat heaters were activated).

 

[Sophias_dad]

Preheating definitely turns on the seat heaters(ALL), and I believe it determines which level of heating depending on the temperature of the interior/exterior.

 

[StealthP3D]

Preheating definitely turns on the seat heaters(ALL), and I believe it determines which level of heating depending on the temperature of the interior/exterior.

That's good to know. I'm surprised it does it without indicating on the display or the phone app.

When you say "all" seat heaters, you mean the rear ones too? That would seem like a waste of battery power if there are only one or two occupants. Yes, I know, they probably only draw 100-150 watts each (on high), but still...

 

[SVMike]

I thought I noticed that the driver seat heater had come on at least once.
But a few times after that I noticed that it has not come on.
Maybe it is based on the external and internal temperatures?

I also noticed that just once when I activated pre-heating I got a message on my phone that it was defrosting the car.
This made sense since the car was parked outside, unlike normal, in a place I typical get moisture and do need to run the defroster.
Other times I've been parked in my garage or a work garage.

 

[StealthP3D]

I thought I noticed that the driver seat heater had come on at least once.
But a few times after that I noticed that it has not come on.
Maybe it is based on the external and internal temperatures?

I also noticed that just once when I activated pre-heating I got a message on my phone that it was defrosting the car.
This made sense since the car was parked outside, unlike normal, in a place I typical get moisture and do need to run the defroster.
Other times I've been parked in my garage or a work garage.

Yes, our Model 3's say "defrosting" in the phone app more than half the time in the cooler months. And I think it might actually have a humidity sensor in the cabin. Because it can be pretty cold and NOT say "defrosting" or pretty mild and say "defrosting" when using the phone app to pre-heat. I'll have to keep a closer eye on temps and humidity to see how it decides.

 

[Sophias_dad]

That's good to know. I'm surprised it does it without indicating on the display or the phone app.

When you say "all" seat heaters, you mean the rear ones too? That would seem like a waste of battery power if there are only one or two occupants. Yes, I know, they probably only draw 100-150 watts each (on high), but still...

Yes, it's definitely running even the rear seat heaters. It was pointed out to me and even the center one was very warm, almost hot, to the touch even though no one had sat in it at all. Had to have been on setting 2 or 3, although I didn't check the screen. It sounds like the screen doesn't show them on anyway, and I suspect they turn off the moment you open the door.

As far as wasting power, yes they probably waste a bit, but think of all the seating materials the air no longer has to warm up. Also, once they get to be significantly above the interior temperature, they'll be heating the air too.

 

[SVMike]

Last evening when I started the remote climate feature it immediately showed me a seat heater icon...a few seconds later it showed me a defrost icon and said defrost on (or something similar). That was at 10pm after a few hours outside.
This morning, in my garage, I turned it on and saw neither of those, just the dash heat came on.
So I've now seen 4 different modes: just heat, heat + seats, heat-defrost, heat-defrost+seats.

 

[Sophias_dad]

Last evening when I started the remote climate feature it immediately showed me a seat heater icon...a few seconds later it showed me a defrost icon and said defrost on (or something similar). That was at 10pm after a few hours outside.
This morning, in my garage, I turned it on and saw neither of those, just the dash heat came on.
So I've now seen 4 different modes: just heat, heat + seats, heat-defrost, heat-defrost+seats.

Yep, that sounds right.