Why don't car heating/cooling systems shut off entirely once a temperature is reached?

Eric

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This is a question that's plagued me for a long time now. In your home it just shuts off when the desired temperature is reached and this is seems logical, cars are incapable of this and it's obviously by design. Instead they run fans the entire time, as a result I'm constantly turning it off and on, which is now a 3 step process in the new shitty BMW design.
 
Totally different environments, total space, heating/cooling dynamics, etc. If the system shut off completely, the cabin would keep warming or cooling, so instead of turning off, it just dials way back and makes small adjustments. Also in a car, the the get stale pretty quickly (with the windows up) the HCAV keeps air circulating (in a relatively small airspace).

We set it and forget it for the most part.
 
Totally different environments, total space, heating/cooling dynamics, etc. If the system shut off completely, the cabin would keep warming or cooling, so instead of turning off, it just dials way back and makes small adjustments. Also in a car, the the get stale pretty quickly (with the windows up) the HCAV keeps air circulating (in a relatively small airspace).

We set it and forget it for the most part.
They're making an assumption on our behalf, what works for you does not work for me, which is not using fans to control both ends of the spectrum and simply turning it off. Once it's perfect at 72 it automatically starts cooling. There should be options, it's not a matter of safety but preference.
 
My point about why do cars operate the way they do versus a home AC is that they’re a totally different environment. A 2500 square-foot home with 8 foot ceilings is like 20,000 cu/ft of airspace versus a midsize SUV which is about 130 to 140.

Now within those constraints that a car HVAC system has to operate completely differently? Yeah I do understand the automatic AC in modern cars can be a little sketchy. I absolutely hated the one in the Tesla.
 
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The blower (with the burner off) in our home furnace system runs for an extra minute or so after the desired temperature is reached. That's to push the remaining heated air in the ducting out into the living spaces.
 
They're making an assumption on our behalf, what works for you does not work for me, which is not using fans to control both ends of the spectrum and simply turning it off. Once it's perfect at 72 it automatically starts cooling. There should be options, it's not a matter of safety but preference.
It’s physics. Fan/compressor/heat need to keep running in order to maintain the temperature. If they don’t, then when the target is reached and it shuts off, the temperature will immediately change again.

There are additional issues due to mechanics, depending on the type of car (ICE vs EV, etc.) and whether you need to heat or cool.

Additionally, depending on the car, and whether you have recirculation turned on or off, fans will be on to recirculate the air or to bring in outside air.

If your house was the same size as a car and had glass walls, your home HVAC would have to operate the same way.
 
The blower (with the burner off) in our home furnace system runs for an extra minute or so after the desired temperature is reached. That's to push the remaining heated air in the ducting out into the living spaces.
Ours does the same and I understand that's part of the HVAC system, cars should be able to do the same, reach the designated temperature, clear out and then shut off. The physics of space shouldn't matter as long as the same principles are applied for the designated space/mechanics.

Let's put it this way. I can manually turn it off and on all I want to achieve the desired comfort level without issue, the car should be able to do the same.
 
One reason I want a new truck, besides screen envy, is that the new Ford's have a 3-speed fan setting when in AUTO. So basically if you have the temp set, the AUTO will try and keep it there, but sometimes the fan speed is too much or not enough, so you hit the fan button to change it, but that kills the AUTO feature. So Ford made it there are 3 fan speed on AUTO and pressing the AUTO button cycles though them. Works pretty well.
 
One reason I want a new truck, besides screen envy, is that the new Ford's have a 3-speed fan setting when in AUTO. So basically if you have the temp set, the AUTO will try and keep it there, but sometimes the fan speed is too much or not enough, so you hit the fan button to change it, but that kills the AUTO feature. So Ford made it there are 3 fan speed on AUTO and pressing the AUTO button cycles though them. Works pretty well.
That's smart. The main reason it's an issue for me now is because BMW now makes you click the climate control to enter the screen, then you you toggle it on, then you have to tap again to get out of it. It's a 3 step process just to turn it on or off which is ridiculous.

Prior to this you had a simple on off button on the dash, for example, after the desired heating temp is reached and it starts blowing cold air immediately after to counter it you could just shut it off manually with a single press of the button. They've just made the entire process way more complicated in the name of tech, I guess.
 
I have what seems to be an odd preference, which I got from my mother (along with the annoying habit of lengthy sneezing fits for no apparent reason). My feet get cold, so I like warm air down there, which gradually rises. But I prefer to breathe cold air, because warm air make me sleepy, which is kind of a bad thing while driving. It seems to me that cars in the past could do the split, but now that cars are so much better, that is not an option. And if the windshield needs to be warmer than fogged up, well, I am just screwed.
 
I have what seems to be an odd preference, which I got from my mother (along with the annoying habit of lengthy sneezing fits for no apparent reason). My feet get cold, so I like warm air down there, which gradually rises. But I prefer to breathe cold air, because warm air make me sleepy, which is kind of a bad thing while driving. It seems to me that cars in the past could do the split, but now that cars are so much better, that is not an option. And if the windshield needs to be warmer than fogged up, well, I am just screwed.
It seems like the ability to split the airflow still exists but it's convoluted and buried within sub functions in order to change/access, I'll say that Tesla did have a pretty intuitive interface when it came to that though. Still, long gone are the days when you had simple and clearly labeled buttons/dials/sliders on the dash.
 
I have what seems to be an odd preference, which I got from my mother (along with the annoying habit of lengthy sneezing fits for no apparent reason). My feet get cold, so I like warm air down there, which gradually rises. But I prefer to breathe cold air, because warm air make me sleepy, which is kind of a bad thing while driving. It seems to me that cars in the past could do the split, but now that cars are so much better, that is not an option. And if the windshield needs to be warmer than fogged up, well, I am just screwed.

I don't remember which car it was, but I had one that would do just that. Warm air at feet, but cooler air from the vents.

It seems like the ability to split the airflow still exists but it's convoluted and buried within sub functions in order to change/access, I'll say that Tesla did have a pretty intuitive interface when it came to that though. Still, long gone are the days when you had simple and clearly labeled buttons/dials/sliders on the dash.

1980's BMW's. They had 3 sliders for the floor vents, the main vents and the windshield vent. Set them where you want them in any combination. Worked very well and probably my favorite non-AUTO car HVAC system.
 
I have what seems to be an odd preference, which I got from my mother (along with the annoying habit of lengthy sneezing fits for no apparent reason).
I’ve had the same tendency for many years, sometimes sneezing 30 or more times in a row. I also used to get annoyed when it happened, but I eventually learned to let it run its course. Fortunately, I don’t recall it ever occurring when I was driving or doing some other activity that couldn’t withstand the interruption.
 
I have what seems to be an odd preference, which I got from my mother (along with the annoying habit of lengthy sneezing fits for no apparent reason). My feet get cold, so I like warm air down there, which gradually rises. But I prefer to breathe cold air, because warm air make me sleepy, which is kind of a bad thing while driving. It seems to me that cars in the past could do the split, but now that cars are so much better, that is not an option. And if the windshield needs to be warmer than fogged up, well, I am just screwed.

Our iX does split control, including temp, so I can have warm in the footwell, and cool on the face :)
 
Our iX does split control, including temp, so I can have warm in the footwell, and cool on the face :)
Just tested with mine and it's a 5 step process. All touchscreen and submenus while driving. Maybe not exactly the same on yours but it's likely similar and takes a similar amount of steps. This is beyond ridiculous for any car, they've taken a perfectly functional system of simple on/off dash controls and dials and forced it into a messy convoluted system.

1) Open the climate control system
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2) Turn it on
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3) Go into Individual Settings
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4) Make your changes
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5) Close the climate control system
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I’ll be honest: i can’t quite figure out how the damned AC/heat works on the i4 and iX. I just set it to a temperature and don’t touch it unless it’s to turn on the seat air conditioning.
 
I’ll be honest: i can’t quite figure out how the damned AC/heat works on the i4 and iX. I just set it to a temperature and don’t touch it unless it’s to turn on the seat air conditioning.
This. I also use my window to control the temp if it gets too hot or cold, just too much of a pain in the ass to tweak it while driving. What's really ironic about any of these cars and all of their menus is how they tell you to text while driving but it's somehow okay for you to try and navigate nonsensical touch screen menus while scratching your head to try and achieve basic functions.

I'm with you though, I just leave most of it alone and if I really feel like I need something I'll play with it while parked or warming the (ICE) up before taking off.
 
This. I also use my window to control the temp if it gets too hot or cold, just too much of a pain in the ass to tweak it while driving. What's really ironic about any of these cars and all of their menus is how they tell you to text while driving but it's somehow okay for you to try and navigate nonsensical touch screen menus while scratching your head to try and achieve basic functions.

I'm with you though, I just leave most of it alone and if I really feel like I need something I'll play with it while parked or warming the (ICE) up before taking off.
This is why i want carplay ultra. If the car manufacturers can’t even make a decent AC interface, let apple take over. And it’s why I’m worried about the next iteration of BMW’s interface - taking away even more physical controls is not going to make things easier.
 
This is why i want carplay ultra. If the car manufacturers can’t even make a decent AC interface, let apple take over. And it’s why I’m worried about the next iteration of BMW’s interface - taking away even more physical controls is not going to make things easier.
It's hard to know why they're making this decision, it's like they feel the need to keep up but it's just making it worse. There are plenty of studies showing drivers prefer getting away from touch screen so it seems like an odd decision. I won't give up on them yet though, still hands down the best cars I've ever owned.
 
This is why i want carplay ultra. If the car manufacturers can’t even make a decent AC interface, let apple take over. And it’s why I’m worried about the next iteration of BMW’s interface - taking away even more physical controls is not going to make things easier.
Does Apple make the interface for vehicles that use CP Ultra or does the manufacturer make the interface? Because if it is the latter, I dunno how CP:U would make things better. I would also be curious if it would remove options/choice from the end user. It is a shame that only Aston Martin has this feature. After the initial previews no one seems to be talking about how it is to live with day to day (surprised C&D or Motor Trend doesn't have one as a long term car specifically to review CP:U).

Tesla does offer fan speeds for auto (I think they added this 2-3 years ago) where you can set the fan speed to low-med-high while keeping the temp settings on auto.

So my mini-split (room over garage) allows auto setting for a single temperature, but my ecobee (rest of house) does not, it has you select a cool/heat temp setting and it won't let them be the same (last time i checked, which has been a while). My mini-split always runs (like a car) where the ecobee actually turns off the ac/furnace when in between the set temps. Sounds like you would want the ability to say car should get no warmer than x and cooler than y and have those temps be some degrees apart so the system can turn off. I wonder how long the system could stay off, as in how quickly a car in motion cools down in the winter or heats up from the sun in summer.
 
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