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Car Forum / Ford / Ford Trucks / September 2005

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General AC question

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Doug - 23 Aug 2005 18:32 GMT
Hey everyone,

Does switching from Normal AC to MAX AC do anything besides blow harder?
Does the compressor pressure up more or something or what happens exactly??
Not important, but just curious for some time about this.

Regards,

Doug
Stephen - 23 Aug 2005 18:55 GMT
> Hey everyone,
>
> Does switching from Normal AC to MAX AC do anything besides blow harder?
> Does the compressor pressure up more or something or what happens exactly??
> Not important, but just curious for some time about this.

I wondered about this myself a few months ago so I looked at my manual.
 I wanted to know which setting used the compressor.

Normal AC takes air from outside the cabin and cools it.  The air
outside might be very hot so it takes a lot of cooling to bring the
temperature.  Max AC cools and recirculates cabin air.  That means that
it is further cooling air that it has previously cooled but it also
means you aren't getting much fresh air in the cabin.  Use MAX AC when
you first get in and the cab is blasting hot then switch to Norm.

Max AC and Off are the only settings that don't bring in outside air.
This is handy if you get behind a smoking truck, run through a dust
cloud or most importantly travel through an area recently visited by a
skunk or past a mushroom farm.  It's not recommended to use MAX AC or
Off for long periods of time because the cabin air can become stale.  I
haven't really found this to be true with Max AC but I have for Off.

Off, Panel and Floor are the only settings that do not use the AC
compressor.  Panel+Floor does.  So if it is cool, you might save a few
farthings on gas by using those settings.  Most of the time it's
probably not worth it since AC tends to keep the windows clear.

Stephen
SC Tom - 23 Aug 2005 21:42 GMT
<<snip>>  Use MAX AC when
> you first get in and the cab is blasting hot then switch to Norm.

That depends on where you live. Here in SC when it's 95 degrees out with
humidity to match, it's best to start with outside air, then move to max air
after a few minutes. The temp inside my car has been 150 in the full sun,
and trying to cool that rather than the 95 degree outside air is pretty
futile.
Just my $.02, FWIW.

SC Tom
Doug - 23 Aug 2005 22:27 GMT
Alright, thanks guys!!  I've actually wondered that for years, and just kept
forgetting about it when in front of this thing until today!  It's one of
those things that's not important enough to be hell bent on an answer, but
something just to satisfy curiosity!

Once again,  thanks,

Doug

>> Hey everyone,
>>
[quoted text clipped - 25 lines]
>
> Stephen
TranSurgeon - 23 Aug 2005 22:33 GMT
some vehicles actually speed up the fan on 'MAX', but on some it just SOUNDS
faster cause the fan noise is ducted back intothe cab on the intake side

> > Hey everyone,
> >
[quoted text clipped - 25 lines]
>
> Stephen
Stephen - 24 Aug 2005 01:09 GMT
I think it might have something to do with cab air pressure.  I took the
back seat out for trip this month and I discovered something kinda
interesting.  Of course there was more road noise without the seats and
seat backs but the cabin vents at the back of the cab were exposed.
They are small rectangular openings with sort of louvres made of
flexible material.

Cab pressure drops when MAX or Off is used, which makes sense because
you are not forcing air into the cab.  You can actually see this as the
vents are open with most settings and closed on MAX and OFF.  With
nothing to slow the increase/decrease in pressure, you could also feel
your ears pop when switching back and forth.

So...I speculate that maybe when you switch to MAX the fan has less
resistance, that is, that it is not trying to stuff more air into the
cab and increase pressure so it speeds up a little.

Stephen

> some vehicles actually speed up the fan on 'MAX', but on some it just SOUNDS
> faster cause the fan noise is ducted back intothe cab on the intake side
[quoted text clipped - 31 lines]
>>
>>Stephen
JohnR66 - 25 Aug 2005 00:47 GMT
>I think it might have something to do with cab air pressure.  I took the
>back seat out for trip this month and I discovered something kinda
[quoted text clipped - 14 lines]
>
> Stephen

I noticed the pressure on my ears when I switch from MAX to just AC in my
Ranger. I never noticed that in other cars. I'll have to take my altimeter
with me to see how much pressure change there is.
John
dwayne - 08 Sep 2005 16:38 GMT
It blows harder, and closes the damper so it recirculates inside air to be
re-cooled instead of outside air being cooled. Nothing changes as far as the
compressor goes.
> Hey everyone,
>
[quoted text clipped - 5 lines]
>
> Doug
 
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