Car air conditioning: fresh air vs recirculate?

[Pajamarama]

Today, my wife and I had a little argument/discussion re: car air condition as we drove around on a hot June day.

My view: when it's cool out, keep it on fresh air. When it's hot out, keep it on recirculate. Keeping it on recirculate means you don't have to keep cooling down hot air from outside.

Her view: it is better to keep it on fresh air all the time. The A/C will cool the air enough so you wouldn't notice any change in temp. And the most important part was you kept getting fresh oxygen into the cabin to prevent getting sleepy. (I thought this was an interesting point but totally bogus)

Who's right -- Me, her, both or neither?

 

[Hollow]

You.

 

[yonyon]

For the most part, you. Her "fresh oxygen" angle isn't too far off though, as keeping the AC on recirc can give you very dry air eventually. There's no way you'll have a lack of oxygen, but a lack of humidity can give some people a drowsy feeling.

 

[Chris142]

I don't know about your car but mine has a hard time cooling off hot outside air. When I get in mine and it's hot I run it on fresh with a window cracked to help push the hot air out. After a few minutes I put it on recirculate and close the windows.

 

[Coprolite]

FE will suffer when it is hot. Oxygen levels won't vary enough to make you drowsy. The most important consideration is outside air quality. You don't want to breath pollution....

 

[Nick R]

Most of the time I leave mine on Fresh air. I know it probably hurts fuel efficency, but I generally dislike recirculate. Mine doesn't really have an issue cooling it off, unless it's really hot out and I'm idling. I dunno.

 

[BrownBox88]

I keep my on recirc and it keeps the cabin filter cleaner than when I had it on fresh air on trips from Pensacola.


Women logic is always different

 

[antonmnster]

There's still plenty of "fresh" air even if it's on recirculate. But I don't use recirc unless it's really warm out. Lately I've left my car on auto-recirculate; it opens and closes the flap depending on a number of factors including air quality. Gotta love the over-engineered german cars.

 

[Dakota1820]

women are always right even when they arent. but your right but just nod smile and go ok honey

works for me . lol

 

[JHZR2]

Her.

Offgassing of plastics and pollution from you and that makes its way into the car builds up. Multiple studies have found that the air inside of a vehicle is amongst the worst that you can breathe.

I rarely use recirculation, generally only if it is REALLY hot to cool down faster, then I transition back over to fresh air as soon as I can. If Im going through a place where it looks like the air is dusty or a plume of pollution has formed (say from a sooty truck, going through the Lincoln Tunnel, etc), I then go to recirc but again shift back.

In really nasty places like FL, I may bias a bit more towards using the recirculation because of conditions like excessive humidity. I always change back as soon as possible.

Down in the Caribbean, many folks leave recirc on all the time. I find that the air in the cars smells worse than cars that are left on fresh as much as possible.

There may be something to be said about mold formation and dry air by using recirc, but Im not sure it makes any difference.

I prefer her choice, but am willing to use recirc for short, specific periods as needed.

 

[Eddie]

Some really good points here that I had not thought about, especially the plastic outgassing. I use recirculate for a rapid cool down and leave it in recirc if I am in stop & go traffic. If I am out on open road, I then switch to fresh. When I was in NJ, I had to use rec 90% of the time.)

 

[NateDN10]

If it's really hot out, I'll use recirc for the first few minutes, until it cools down, then switch to fresh air. Even on hot days, it gets very cold in the car to keep it on recirc the whole time!

 

[mpvue]

my car pool buddy loves using recirc, using it all the time but the glass fogs up on cool mornings or hot humid rainy days.
I also find the air smells different after awhile in recirc.

 

[The_Jeff]

On a tangent but I live in a low crime area and leave my windows down in the driveway or even work parking lot. This helps the outgassing. Plus my cars are 15 years old so the plastic's probably pretty brittle and, well, done with that new car smell.

I think you should keep it on recirculate all the time because it's cheaper. If the compressor doesn't have to work as hard you get better gas mileage. Cars aren't submarines or space shuttles; they leak enough oxygen so you can breathe. Since they put air bags in they put these huge vents in, typically in the rear door opening, so the air bag explosion doesn't blow out your ear drums. (Don't start lecturing me on lack of pressure differentials.

)

My experience with mostly GM cars is they have ventilation whether or not you want it, as evidenced by chilly drafts at my feet when it's supposed to be completely "off" on a cold start. The miser-specials I've had without AC lack the recirc flap too. In fact I'd buy a car with dead AC over one without it just to get the recirc flap in the heater core box!

 

[Hokiefyd]

Both of our cars have automatic HVAC systems, and I would think that the way an automatic HVAC system operates would be closest to "correct", as I imagine the OEM has done more R&D on the issue than nearly anyone else.

When we start either one on a hot day, the RECIRC light will immediately come on, and the system will stay in RECIRC mode for a duration of time that pretty closely correlates with the ambient temperature. The hotter it is, the longer the system stays in RECIRC. If it's hot enough outside, it will sometimes always stay in RECIRC mode. If it's in the 80s, it'll usually stay in RECIRC mode for 5-10 minutes then revert back to fresh air.

We of course have the option of manually selecting RECIRC (or turning it off if it's already on), but I typically let the system do as it is designed to do. The only exception is if they're doing prescribed burning and it's notably smoky outside, or if I do see a plume of PM ahead.

 

[Falcon_LS]

Personally, I roll down all the windows for the first 3 minutes or so of driving with the AC on recirculate to get the hot air out. It remains on recirculate, until I'm about to reach my destination, when I start to induce outside air. Then I switch to vent to clear the evaporator core, and allow outside air in whilst the car is parked. This is, of course, when the weather is clear and not dusty.

 

[bigmike]

Some of the year, I can get away with keeping my windows down on my trips to work and sometimes on my trip home in the afternoon.

Then, we get 8 months of summer and it's RECIRC or die of heat exhaustion.

I typically roll the windows down for the first 10-20 seconds of driving even when it is really hot outside, because even though I managed to barely get through thermodynamics, I have realized that when it's 140F inside the car and 98F outside, there still is some cooling happening.

I believe this is even recommended in the Honda owner's manual, surprisingly.

 

[TFB1]

If the temp is over 80* and humidity high, you can bet mine will be on re-circ...

I consider things like plastic out gassing mostly hysteria, even using re-circ there is some outside air introduced into the cabin... If not you'd have a bunch of wrecks from passed out drivers due to lack of oxygen...

 

[1999nick]

I have always used recirculate only for a few minutes when getting into a hot car. I have never had a car that would not provide satisfactory cooling in fresh air mode.

Every car I have owned has been very noisy in recirculate mode, and I have always gotten out of that mode as soon as possible.

 

[mechtech2]

You are right.
Recirc cools much better.
But, it does not dry the air out as much - this can be a factor.
And fresh air? I have not seen any people passed out from lack of O2 when using recirc, but fresh air is good.
I always use recirc when starting, then usually go to fresh air.