Car climate control sometimes starts on recirculated air?

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MadEngineer

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Topic # 185877 8-Dec-2015 19:11

Does anyone know the logic or reasoning behind this? When I start the car when it's been baking in the sun or there is otherwise a large difference between the outside and inside air it seems the climate control sets the air to recirculate. AC only seems to come on in the auto mode when the temp is set to the lowest position.

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Reply # 1443038 8-Dec-2015 19:18

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A/C is more efficient using air from within the car rather than outside. Most cars default to recirculate when you turn the A/C on.

richms

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Reply # 1443077 8-Dec-2015 20:08

Once the car is cooler than outside, yeah. But initially when its 45+ degrees in the car, no. Im lucky enough to still have a slide control for it in my cars so can easily adjust it as I want.

Richard rich.ms

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Reply # 1443082 8-Dec-2015 20:22

sbiddle: A/C is more efficient using air from within the car rather than outside. Most cars default to recirculate when you turn the A/C on.

isn't the recommendation to open your window when driving around town and to use the ac with windows up when on the open road? it doesn't explain with the car would recirculate the air, especially when the AC isn't on and the car isn't moving

also recirculating the air eventually just makes the windows fog up when it's cooler outside

richms

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Reply # 1443093 8-Dec-2015 20:38

And let smelly diesel fumes in? No thanks. Recirc all the time except when the car is really hot from being parked.

Aircon will remove the moisture from the air, so fogging up shouldnt ever be a problem.

Richard rich.ms

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Reply # 1443118 8-Dec-2015 20:49

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If the car is scorching hot when I get in then I open the window for a few minutes to let out the excess heat, then roll up the windows and operate the air conditioning. As others have mentioned, recirculate will allow the AC to bring the cabin temperature down to a comfortable level more quickly but make sure you switch back to fresh air to avoid fatigue if you are on a long trip.

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Reply # 1443119 8-Dec-2015 20:52

richms: And let smelly diesel fumes in? No thanks. Recirc all the time except when the car is really hot from being parked.

Aircon will remove the moisture from the air, so fogging up shouldnt ever be a problem.

Agree with this.. On a hot day after car has been parked up i open windows and sunroof even just for a couple of minutes which gives the AC a fighting chance to bring temp down fairly quickly, by the time I'm out of the car park, windows back up, car almost pleasant, mind you I have tinted windows which definitely help the cause given black leather interior

scuwp

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Reply # 1443174 8-Dec-2015 21:55

Because it's easier to cool a carload of air faster than to cool all the air in the atmosphere. Initially it seems like a bad idea but it really does work once the initial cooling process starts.

Always be yourself, unless you can be Batman, then always be the Batman

richms

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Reply # 1443179 8-Dec-2015 22:00

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I only ever put the window down to place my food order or to pay or collect it.

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Reply # 1443344 9-Dec-2015 09:35

To cool the car quickly you want the air coming out of the aircon to be as cool as possible. To do that you want the air entering the aircon to be as cool as possible. So if it's cooler outside it's better to use outside air. When it's hotter outside it's more efficient to use re-circulation.

(Slight simplification because the moisture content comes into it as well, but it doesn't make much difference.)

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Reply # 1443348 9-Dec-2015 09:40

Maybe you should buy a Ford. (the Non Aussie ones). THey all default to using outside air no matter what you do the last time you used the car.

trig42

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Reply # 1443355 9-Dec-2015 09:45

All climate control A/C (usually the Auto button/Option in newer cars) will default to Recirc when first turned on/activated.
Mine pulls down the temp pretty quickly (Mazda3), then switches over to fresh air (usually after about 3 minutes).
If it doesn't switch to fresh air, then there is something wrong.

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Reply # 1443358 9-Dec-2015 09:47

richms: I only ever put the window down to place my food order or to pay or collect it.

...or when the nice man in uniform asks you to.

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Reply # 1443360 9-Dec-2015 09:48

I have read (but can't find again) a report on research undertaken in Europe where the authors concluded that people are more like to crash if they have their A/C set to recirc. The author's believed that reduced oxygen levels affected concentration and exacerbated fatigue. They recommended that A/C be designed to switch to fresh air after 15 minutes (or something like that) on recirc.

Mike

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Reply # 1443378 9-Dec-2015 10:20

Mine stays on outside air unless the air quality sensor detects low quality air, then it changes to recirculate

From the BMW Website:

Automatic Air Recirculation (AAC) delivers noticeably better air quality in the cabin of your BMW. The system recognises pollutants and contaminants in the outside air and removes them in a microfilter. Should the concentration of pollutants exceed a maximum level, the system automatically closes off air intake from outside and temporarily recirculates the air in the cabin.
The condensation sensor ensures that the windows of the vehicle do not become misted, even if humidity levels increase. In addition, the solar sensor measures the intensity and angle of the sun's rays, and the system automatically adjusts the air conditioner's performance to ensure a steady temperature is maintained. You and your passengers enjoy a steady cabin temperature, a clear view and excellent air quality at all times.

It does seem to work anyway

Matthew

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Reply # 1444413 9-Dec-2015 11:47

scuwp: Because it's easier to cool a carload of air faster than to cool all the air in the atmosphere. Initially it seems like a bad idea but it really does work once the initial cooling process starts.

this would make sense if a) the air con also came on with the recirculate function and b) if if was efficient to use ac, should I turn it on rather than open the windows. But generally it doesn't

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