Defroster Vent UI Behavior

[scaesare]

A question on defroster vent behavior: is it possible to enable the defroster vent for fresh air without also enabling the A/C compressor?

I often like fresh outside air in the cabin at ambient temperature with no heating or cooling applied. I can accomplish this in the HVAC control panel by tuning the A/C Off, Enabling Non-re-circulation, and selecting Dash and/or Floor vents. I then set the Temp = Lo on the "main" lower panel.

However, as soon as I select the Windshield vent, it appears the A/C compressor kicks in, as the temp starts dropping.

There is a separate set of front & rear defroster buttons on the main lower panel. I was hoping that as long as this front-defroster button remained disabled, I could keep the compressor from kicking in. Instead it just appears that enabling this main button is just a "shortcut" that quickly selects a preset that selects the windshield vents, cranks up the blower, etc...

Has anybody discovered a way of doing what this?

Thanks.

 

[mknox]

In theory, the temperature shouldn't drop. The a/c kicking in helps to dehumidify the air which is then subsequently re-heated to the cabin temperature setpoint. (Max defrost turns the heat up to High). At least this is how I believe it works.

In the past I would quite often leave my cars on Auto, but with a/c disabled to save gas. I was doing this in the Model S too until I started to wonder if the a/c compressor is actually a heat pump. Disabling it in the cooler weather would mean that I am relying exclusively on resistive heating if my assumption about the a/c compressor is correct. So for now, I've gone back to full Auto and let the car decide.

 

[scaesare]

In theory, the temperature shouldn't drop.

Yeah, perhaps if I cranked the temp back up to the outside air ambient temp, perhaps it would.

But I don't want to waste energy on that... one of the reasons I do this is because I enjoy the unprocessed outside air at certain times of the year (such as the fall).

On other vehicles I've owned, if I take the HVAC system off of "Auto" and/or disable A/C, I can get fresh air from all vents without the system foobling with it.

 

[mknox]

But I don't want to waste energy on that... one of the reasons I do this is because I enjoy the unprocessed outside air at certain times of the year (such as the fall).

Agreed. I do the same thing. If you set it to full Auto, then manually select a/c Off, you will, as you say, get those results, but I'm not clear if the software will allow that on Defrost. For me, I think if I select Defrost it's because I need it and so wouldn't worry too much about the a/c running since it actually helps. With the windshield clear, I'd then switch back to my earlier settings which unfortunately entail a bunch of extra clicks to make sure the compressor stays off. It would be nice if switching Defrost off from the dedicated button would put the HVAC system back to where it was before, but that doesn't seem to be the case.

I've also noticed that when I use the app to pre-heat the car it puts the system into full Auto, and when I get into the car, I have to remember to manually set the a/c back Off again.

 

[Doug_G]

I've also noticed that when I use the app to pre-heat the car it puts the system into full Auto, and when I get into the car, I have to remember to manually set the a/c back Off again.

Hate that; it should go back to your previous setting. This used to be a huge problem with the defrost button, before it had two speeds. You'd hit the button and a few minutes later the car would be a sauna. Then you'd turn it off and it would go back to default settings with a fan speed so low that the car would frost over again.

That said, the Auto settings work a LOT better than they used to. I now leave it in Auto most of the time. We'll see how that holds up when we hit the real winter...

 

[scaesare]

Indeed... I was hoping that the UI just acted as a vent selector on the pop-up panel, and that the actual defrost functioDefrost was globally controlled by the "Defrost Button" on the main lower panel.

It appears not however... and unfortunately turning "Auto" off doesn't really prevent the car from automatically deciding to override the fact I've disabled the A/C.

One thing I don't like in UI's: If you expose the advanced functionality for me to make specific choices (i,e, manually configure the settings and turn off "Automatically Do It For Me" mode), then don't start trying to out-think me.

 

[jerry33]

Hate that; it should go back to your previous setting.

Me too, but I've found that the car "blinks" for a bit after the pre-conditioning is turned off, so I've developed the habit of turning it off using the App before I actually go out to the car.

 

[brianman]

My version of "Vent" mode is:
- AC off
- No recirc
- Windshield vent only
- Fan at 1

This has been reliable for me keeping the front window fog free, such that I haven't needed to use the defroster.

I also put the seat heater on at least 1.

 

[scaesare]

My version of "Vent" mode is:
- AC off
- No recirc
- Windshield vent only
- Fan at 1

This has been reliable for me keeping the front window fog free, such that I haven't needed to use the defroster.

I also put the seat heater on at least 1.

The intent of my original post was to enable venting for fresh air in the cabin from the dash vent (as well as the others), but without engaging the A/C compressor, as I subsequently described. Is that what you are getting?

Otherwise what you are describing is what I would consider a "defrost" mode, as opposed to just vent.

 

[mknox]

Me too, but I've found that the car "blinks" for a bit after the pre-conditioning is turned off, so I've developed the habit of turning it off using the App before I actually go out to the car.

"Blinks" ??? I just get in the car and go. So far haven't noticed any issues.

- - - Updated - - -

I also put the seat heater on at least 1.

I use the seat heater to warm the seat up, then turn it off. Even at 1, I find it is too much and I feel like I've wet myself :smile: I loved how my last car let me control the heat on the seat and the seatback independently. With a sore back, it was nice to turn the backrest up high but leave the seat bottom off.

 

[PaceyWhitter]

I don't know that I have been in a car that allowed the windshield vents on without the A/C kicking on. It might be a safety feature as that setting could create condensation on the inside of the windshield.

 

[scaesare]

I don't know that I have been in a car that allowed the windshield vents on without the A/C kicking on. It might be a safety feature as that setting could create condensation on the inside of the windshield.

Car makes I've owned that allow this behavior:

Toyota
Ford
Mazda
Nissan
Chevy
Dodge

My Mercedes may not have, I don't remember....

 

[PaceyWhitter]

Car makes I've owned that allow this behavior:

Toyota
Ford
Mazda
Nissan
Chevy
Dodge

My Mercedes may not have, I don't remember....

Are you sure that the A/C is not kicking on? I had a Toyota that had a separate A/C button with a light and you could turn that light on or off with the button, but the compressor remained on if defrost was selected.

I do not think that this behavior is mandatory though.

 

[Gizmotoy]

Car makes I've owned that allow this behavior:
Toyota
Ford
Mazda
Nissan
Chevy
Dodge
My Mercedes may not have, I don't remember....

Honda and Mitsubishi, too. The Honda automatically turns the air one when you select those vents, but you can turn it back off. Mitsubishi just does whatever you tell it without trying to be smart about it, which is typical for that brand.

It's not mandatory, just a Tesla design choice.

I use the seat heater to warm the seat up, then turn it off. Even at 1, I find it is too much and I feel like I've wet myself :smile: I loved how my last car let me control the heat on the seat and the seatback independently. With a sore back, it was nice to turn the backrest up high but leave the seat bottom off.

That sound excellent. Now every time I turn the heater on I'm going to miss that feature. Thanks!

 

[scaesare]

My 4Runner will allow you to enable dash + windshield vents without the AC kicking in. If you go to full defrost position then it will also kick in the compressor.

 

[Doug_G]

- Fan at 1

This has been reliable for me keeping the front window fog free, such that I haven't needed to use the defroster.

Fan at 1 won't keep the windshield clear in cold, humid weather.

 

[Musterion]

A question on defroster vent behavior: is it possible to enable the defroster vent for fresh air without also enabling the A/C compressor?

Scaesare, have you tried switching to range mode and then seeing if the A/C compressor still kicks on when you choose the defroster vent? I don't know the answer but have been trying to do the same exact thing you are trying since I got the car.

A second question to everyone who responded: how can you tell if the "heater" is on, i.e. air is being actively heated? It seems that heating is requiring much more energy than cooling (and is an argument against the heat pump theory) and there is no indicator or kill switch for just the heater.

 

[scaesare]

Scaesare, have you tried switching to range mode and then seeing if the A/C compressor still kicks on when you choose the defroster vent? I don't know the answer but have been trying to do the same exact thing you are trying since I got the car.

A second question to everyone who responded: how can you tell if the "heater" is on, i.e. air is being actively heated? It seems that heating is requiring much more energy than cooling (and is an argument against the heat pump theory) and there is no indicator or kill switch for just the heater.

I haven't tried that... but given that defrosting as a function would still be needed, I'd expect it would simply reduce it's maximum capacity, not stop the A/C pump from kicking in all together. I'll give it a try though... thanks for the suggestion.

As for the heat, there is no way that I can tell for sure that the electric heat isn't active. If I don't want heat applied I simply set the temperature to "LO" which seems to keep them off, although if the outside ambient temp was cold enough they might even activate then.

I think the heat pump systems start to kick in once the motor gets warm enough to heat the coolant. At that point I suspect the electric heater turn off (or at least throttle down).... but this is based on energy usage observation and "smell" (the electric heaters seem to have a distinctive odor in my car... perhaps that will burn off over time). I've only had it cold enough to activate this a few times, so I'm still trying to figure out how it behaves....

 

[brianman]

The intent of my original post was to enable venting for fresh air in the cabin from the dash vent (as well as the others), but without engaging the A/C compressor, as I subsequently described. Is that what you are getting?

Otherwise what you are describing is what I would consider a "defrost" mode, as opposed to just vent.

I don't know for certain, but my impression is that my settings (in the part you quoted) doesn't engage the A/C compressor. In fact, if it does engage the compressor then I think the "AC off" UI is broken (at a design level).

- - - Updated - - -

I use the seat heater to warm the seat up, then turn it off. Even at 1, I find it is too much and I feel like I've wet myself :smile: I loved how my last car let me control the heat on the seat and the seatback independently. With a sore back, it was nice to turn the backrest up high but leave the seat bottom off.

Note that my setting of seat heater 1 is with climate control effectively off. It's the only source of heat from the car to me, when the outside temp is below 98.6F. Unless I'm wearing "too many" layers, it rarely gets me too hot in the fall/winter months.

- - - Updated - - -

Fan at 1 won't keep the windshield clear in cold, humid weather.

I guess Seattle doesn't have "cold, humid weather" IYO then; or my car behaves differently from yours. It's been working fine doing that for the last month or two for me.

I've only seen as low as 35F (with speed as high as 75mph) this year thus far though.

 

[mknox]

I guess Seattle doesn't have "cold, humid weather" IYO then; or my car behaves differently from yours.

When Canadians talk of "cold, humid weather" we are speaking of temperatures well below freezing, but still "damp".

I haven't had my Model S completely through a winter yet, but in my past cars, I always found the best way to keep the windows clear was to over-ride the "auto" settings and turn the fan up to at least 3/4 speed. Sometimes it wasn't even necessary to use Defrost, just the dash vents. IMHO, keeping the air moving is the best solution.