Why do vents default to outside air?

Howard Lester wrote:
> "Rob" wrote
>
>
>>recirc works great to cool a steamy car initially, because it is not
>>only throwing cold air at you, but is taking away the hot inside air.
>>but once the car has cooled you want to switch back to outside air
>>(unless a situation like behind a bus, etc., as you mention).
>
>
> This is all backwards to me

Right. Backwards. It's easier to make already cool air colder, or to
keep it cool--there's less heat to remove to the cooling coils. Also,
same goes for humidity. If you keep pumping super humid air from outside
into the car, the air won't necessarily get as dry as it would if you
use the recirc setting.

I'd guess it's switching back to outside air for safety reasons--these
newer cars are so airtight that one needs a fresh supply or air to
prevent CO poisoning if there were a problem with your exhaust system,
for example. Or as others have suggested, the climate control could be
doing it based on air temp.

"Jeff" > wrote in message
...
> Just wondering--whenever I use the AC, my Accord keeps defaulting to
> outside air (as do most newer vehicles, I've noticed). I drive mostly
> in traffic and don't like to breathe exhaust fumes filling the car, so
> I'm continually resetting it to recirc. But I'm curious as to why
> outside air is the default setting. (?)
>
> 2000 Accord v6 sedan
>
> Jeff

With the cab of the vehicle preasurized with outside air, exhaust fumes
cannot enter the car. As a default outside air ensures carbon monoxide free
air.......................

dale P....................

Howard Lester wrote:

>
> This is all backwards to me, unless it's because I live in a hot, dry
> climate. When first getting into the car, the temperature inside the car can
> be 40 degrees hotter than outside; therefore, here one first needs to use
> fresh a/c.

even easier is to just roll the wondows down and drive for a mile. that
gets the 140+ degree air out.

Once the interior starts to cool off, *then* switch to
> recirculate. The a/c won't have to work so hard, cooling air that is already
> temperate, not at inferno-grade.
>
>

On 9/22/04 10:25 AM, in article , "Howard
Lester" > wrote:

>
> "Rob" wrote
>
>> recirc works great to cool a steamy car initially, because it is not
>> only throwing cold air at you, but is taking away the hot inside air.
>> but once the car has cooled you want to switch back to outside air
>> (unless a situation like behind a bus, etc., as you mention).
>
> This is all backwards to me, unless it's because I live in a hot, dry
> climate. When first getting into the car, the temperature inside the car can
> be 40 degrees hotter than outside; therefore, here one first needs to use
> fresh a/c. Once the interior starts to cool off, *then* switch to
> recirculate. The a/c won't have to work so hard, cooling air that is already
> temperate, not at inferno-grade.
>
>

From another resident of a hot climate - you will get better (read faster)
results if you let it go into recirc and crack the windows several inches
for the first couple of minutes. The AC will cool faster and convection
(warm air rises) plus whatever breeze there might be will draw the
superheated air out the windows.

"E. Meyer" wrote

> From another resident of a hot climate - you will get better (read faster)
> results if you let it go into recirc and crack the windows several inches
> for the first couple of minutes. The AC will cool faster and convection
> (warm air rises) plus whatever breeze there might be will draw the
> superheated air out the windows.

Thanks for that idea - I'll try it. Fortunately, the temperatures around
here in southern Arizona have suddenly cooled to "humane," so really I'm
hoping I don't have to get a chance to try it until next May.

"E. Meyer" > wrote in message
...
>
> From another resident of a hot climate - you will get better (read faster)
> results if you let it go into recirc and crack the windows several inches
> for the first couple of minutes. The AC will cool faster and convection
> (warm air rises) plus whatever breeze there might be will draw the
> superheated air out the windows.
>

Bah, this is still unclear to me with no concensus on the best method. It
is agreed that opening/cracking the windows when first driving will evacuate
the heated air, but afterwards there are 2 camps.

1. Start in recirc and then switch to fresh after temp stabilization.
2. Start in fresh and then switch to recirc.

I think 2 is more intuitive and that's what I do!

"MAT" wrote

> Bah, this is still unclear to me with no concensus on the best method. It
> is agreed that opening/cracking the windows when first driving will
evacuate
> the heated air, but afterwards there are 2 camps.
>
> 1. Start in recirc and then switch to fresh after temp stabilization.
> 2. Start in fresh and then switch to recirc.
>
> I think 2 is more intuitive and that's what I do!

That's what *I* do, too. Now, here are excerpts from the (Accord 2004)
MANUAL. Remember that thing?

* If the outside air is humid, select recirculation mode. If the outside
air is dry, select Fresh Air mode.

* If the interior is very warm, you can cool it down more rapidly by
partially opening the windows, turning on the A/C, and setting the fan to
maximum speed in Fresh Air mode.

HAH!




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How about reading to owner's manual, it's all in there in my book. The
manufacturing
engineers wouldn't have put their recommendations in there if they didn't
think it
would help the owner.

D.

"MAT" > wrote in message
...
>
> "E. Meyer" > wrote in message
> ...
> >
> > From another resident of a hot climate - you will get better (read
faster)
> > results if you let it go into recirc and crack the windows several
inches
> > for the first couple of minutes. The AC will cool faster and convection
> > (warm air rises) plus whatever breeze there might be will draw the
> > superheated air out the windows.
> >
>
> Bah, this is still unclear to me with no concensus on the best method. It
> is agreed that opening/cracking the windows when first driving will
evacuate
> the heated air, but afterwards there are 2 camps.
>
> 1. Start in recirc and then switch to fresh after temp stabilization.
> 2. Start in fresh and then switch to recirc.
>
> I think 2 is more intuitive and that's what I do!
>
>

Elmo P. Shagnasty wrote:
> Cars aren't like modern buildings. ALL cars bring in some fresh air,
> even on recirculate.

Hmmm, if you say so. Certainly my '94 Civic does. ;-)

On 9/22/04 7:44 PM, in article , "MAT"
> wrote:

>
> "E. Meyer" > wrote in message
> ...
>>
>> From another resident of a hot climate - you will get better (read faster)
>> results if you let it go into recirc and crack the windows several inches
>> for the first couple of minutes. The AC will cool faster and convection
>> (warm air rises) plus whatever breeze there might be will draw the
>> superheated air out the windows.
>>
>
> Bah, this is still unclear to me with no concensus on the best method. It
> is agreed that opening/cracking the windows when first driving will evacuate
> the heated air, but afterwards there are 2 camps.
>
> 1. Start in recirc and then switch to fresh after temp stabilization.
> 2. Start in fresh and then switch to recirc.
>
> I think 2 is more intuitive and that's what I do!
>
>

I don't see why there should be a "camp". Get out your thermometer and a
stop watch and try it both ways.

I would be willing to bet that number one will win, and is, in fact, the
recommended procedure in every owner's manual I have seen in the past 15
years or more.