Car AC

October 26, 2004 9:08 PM

Is it safe to always keep the car air conditioner on, and on recirculate? A good idea? Because apparently that's what people in Taiwan do, but I've never seen it done in the US.
posted by calwatch to travel & transportation (10 comments total)

Safe to you or safe to your car?
posted by smackfu at 9:21 PM on October 26, 2004

Both.
posted by calwatch at 9:45 PM on October 26, 2004

It certainly isn't good for your gas mileage. I don't see much of a point in doing it when it's not hot enough to actually need AC. A friend of mine did this even in the dead of winter and it always puzzled me.
posted by zsazsa at 10:00 PM on October 26, 2004

Leaving the AC on means some extra load on the motor at start up, so it has to work harder. I've experienced on older beatdown cars a major difference between AC on/off and how easily the car would start. It is similar to motor response/power loss when driving with the AC on/off. I am in the habit of AC off except when needed. That will help encrease gas mileage also.
Recirculation is more efficient/quicker to cool the temp, but you'll probably notice the staleness after awhile if you don't let it air out. Some cars and trucks (like my Ranger) if left in recirc (aka Max AC) while parked are sealed tight and the inside stews in nastiness on a hot muggy day. Nothing is as wonderful as discoverying that after a long day at work.
posted by sailormouth at 10:16 PM on October 26, 2004

But what about exhaust fumes? I suppose that might be a concern in developing countries with lesser emissions standards.
posted by calwatch at 10:38 PM on October 26, 2004

My BMW manual points out that 'recirculate' recirculates 95% of air and introduces 5% outside air.

This is the same obsessive-compulsive manual that suggests 'when the tape player overheats, listen to the CD or radio for a while until it cools down again' and 'although the BMW has excellent handling characteristics, do not think they will enable you to drive while drunk,' so I take it with a grain of salt; but I'd be surprised if other car makers didn't design their recirculators the same way. They certainly are not going to asphyxiate you.
posted by ikkyu2 at 10:55 PM on October 26, 2004

Yes, it's safe up to a point, although you should change the interior air filter more frequently. Moisture that was formerly trapped by the AC will build up on the filter when the car is shut off, and encourage faster growth of mold or mildew. This is especially worth noting if your car is well sealed or recirculation doesn't introduce a small amount of outside air.

If the interior of the car is cooler than the exterior of the car, running the AC in recirculation mode will be more effective and less strenuous on the compressor. If the car has been warmed in the sun, it's a pretty good idea to run the AC with fresh air for a while until the temperature equalizes, then switch to recirculation.

Running the AC and heat at the same time serves only one useful purpose: dehumidification, for purposes of unfogging the windows. It's otherwise a complete waste.

Modern cars shouldn't experience a power loss when running air conditioning; the computer compensates for the additional load by adding throttle. Unless you're driving with the throttle fully open, you won't notice a difference.

The only reason I can think of to leave recirculation on permanently is if the air on the road is significantly worse than the air inside the car. This could be the case in countries with poor emissions controls, but otherwise shouldn't be applicable in developed parts of the world.
posted by majick at 11:39 PM on October 26, 2004

Running the AC and heat at the same time serves only one useful purpose: dehumidification, for purposes of unfogging the windows.

Exactly, even in the cold of winter.
posted by page404 at 3:54 AM on October 27, 2004

.. but I've never seen it done in the US.

Obviously, you've never lived in Florida.

Also, remember: the air conditioner doesn't only cool the air... it conditions it as well.
posted by bshort at 7:25 AM on October 27, 2004

Just don't be like the people I see driving around all winter desperately scraping viewholes in the ice on the INSIDE of their windows. (They've left the "recirc" switch on.)
posted by Tubes at 11:12 AM on October 27, 2004