HVAC Fresh Air Behavior

Modern cars have a tendency to switch to outside air every chance they get. Some switch to outside every time they start up. I wasn't able to find any regulations (though I didn't look that long) but I suspect there are some because ICE cars are dangerous in ways other than the volatile fuel that they use.

Study came out recently suggesting that we all drive with recycled air whenever possible. Researchers determined that it reduces pollution levels as much as 80% especially on freeways. Apparently automakers aren't on the same page.

apacheguy said:

Study came out recently suggesting that we all drive with recycled air whenever possible. Researchers determined that it reduces pollution levels as much as 80% especially on freeways. Apparently automakers aren't on the same page.

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Not doubting your study, but I am curious how recirculating cabin air cuts down on pollution, especially by 80%. Anyone care to elaborate??

Chipper said:

Not doubting your study, but I am curious how recirculating cabin air cuts down on pollution, especially by 80%. Anyone care to elaborate??

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Well, it would certainly cut down on pollution if there was a smelly diesel car or truck in front of you. However, a car's interior has lots of VOCs, so it might just be trading one form of pollution for another.

jerry33 said:

Well, it would certainly cut down on pollution if there was a smelly diesel car or truck in front of you. However, a car's interior has lots of VOCs, so it might just be trading one form of pollution for another.

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CLICK!!! Did apacheguy mean it would cut down on pollution we are breathing??? I thought he meant using recirculated air would cause our vehicles to create less pollution in our environment. OK...making more sense now.

Chipper said:

CLICK!!! Did apacheguy mean it would cut down on pollution we are breathing??? I thought he meant using recirculated air would cause our vehicles to create less pollution in our environment. OK...making more sense now.

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Exactly. Here is a link for those interested:

'Recirculate' button cuts drivers' exposure to air pollution, study says - Los Angeles Times

scaesare said:

More interesting observations about the HVAC UI behavior.

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I've never noticed this or heard or heard a noise, but I have noticed that using the app to turn on the HVAC always (annoyingly) resets all settings to auto. I almost never want outside air (which is rarely "fresh," given all the gas-powered cars around me).

I have noticed that the fan occasionally gets into this mode where it fluctuates a lot; next time that happens, I'll try to remember to check the icon to see if it's flipping between outside/recirc air! I have noticed that on outside air, the fan generally seems to run lower (i.e., with fan on auto, switching from outside to recirc makes the fan blow stronger).

All in all, I find modern car "auto" settings kinda wacko. ;-)

Yup I've noticed this too. I thought i was going crazy at first and kept toggling auto and the two air options. Very strange behavior to me.

scaesare said:

More interesting observations about the HVAC UI behavior. Last time it was the Defroster Vent. This time it's the Fresh/Recirculating setting...

It appears that even if you disable the "Auto" setting in the control panel, and explicitly set the system for Recirculating air, as seen here:


The system will occasionally decide to switch to Fresh Air mode, as seen here:


It will switch over for a couple of minutes every so often in some circumstances and then switch back. I assume it's when it detects sufficient humidity in the cabin. I can hear the vent noise change, so it's not just a UI thing.

It's not a deal breaker... but I'm not sure shy if you are going to present me with an Auto mode and an option to override it, then why not really allow me to over ride it?

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I noticed this behavior a while ago. Funny thing is that it seems to stop happening if you put the vets on foot and window and not on face. Now I haven't tested that fully so don't hold me to it.

scaesare said:

I have another thread (HERE) where I discuss that enabling the Windshield Vent also activates the air conditioning compressor regardless of whether you have A/C set for on, off, or Auto. I suspect that's why the car is making a different decision about the re-circulation setting...

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That may be the case but from what I have seen you need the foot AND windshield for the re-circulation to stay on.

scaesare said:

Well looky there... I got a reply from Tesla on the email. He said it's been forwarded to the head of their HVAC engineering team, and they are looking at it already based on some similar feedback.

His expectation is that the behavior will be changed in a future FW upgrade. I thanked him, and referred to the A/C compressor and windshield vent behavior as well...

Nice to have a personal response with actual detail, as opposed to a canned form letter.

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Great! Thanks for contacting us and letting us know the good news.

rlang59 said:

I noticed this behavior a while ago. Funny thing is that it seems to stop happening if you put the vets on foot and window and not on face. Now I haven't tested that fully so don't hold me to it.

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I've been noticing the annoying "pull in fresh even though he set it to recycle" thing more and more lately, perhaps because it seems to only happen on heat (on cool, in the summer, I never noticed it...and I hate the smell of exhaust and would've noticed) . . . but something I noticed a couple of times recently, related to what you say here--I changed the vents from auto (it was just on my feet) to feet+windshield and almost immediately, it reverted to recycle. This, coupled with your experience, makes me think that either of these fixes it -- (a) combining feet+something or (b) moving vents from auto to manual -- not sure which it is.

I haven't tested either--tough to test when it is kinda random!

I also noticed that turning the temp down so it started blowing cool air seemed to "fix" it which is absurd, of course. But I'm hoping the "vents on manual" (or "vents including something other than feet") thing works as a work-around. I may just leave it like that and see if it ever blows exhaust at me again. ;-)

scaesare said:

Well looky there... I got a reply from Tesla on the email. He said it's been forwarded to the head of their HVAC engineering team, and they are looking at it already based on some similar feedback.

His expectation is that the behavior will be changed in a future FW upgrade. I thanked him, and referred to the A/C compressor and windshield vent behavior as well...

Nice to have a personal response with actual detail, as opposed to a canned form letter.

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I'm one of those other reports. I emailed ownership several days ago. They sent it to service who called and I clarified and we agreed it sounded like a software bug and they'd send it to engineering.