The compressor on my '02 F350 runs in most settings, regardless of the
temp setting..  Lazy engineering if you ask me.

I doubt SERIOUSLY that there is a problem.  Most auto manufacturers lately
have set the compressor to run on most settings.  Why?  To remove humidity
from the cabin.  It makes sense that if you need to defog the interior of
your windshield, that you have excess humidity.  Most of the time, the
compressor is off on the vent setting and the floor only setting.  Any blend
between floor and defrost will get the compressor.  I can see the logic of
keeping the compressor on when in the floor setting though.  Usually floor
is used for heat in the winter, one of the hardest times of the year to keep
moisture from collecting inside the car (because of snow tracked inside)

CJB

Well if that's how its made I'm not impressed. What I am going to do is
install a switch and turn it off when I want it off and see if my gas
mileage improves.

Thanks to everyone that replied.

That would be exactly how it is supposed to work.  The
reason is humidity reduction to help prevent window fogging
and help keep the cab dried out for those of us who are in
and out in the rain or snow.  Below about 40 deg ambient
temp, the compressor is not used anyway.  It is good for the
compressor to operate some to keep the oil circulating
inside the system.  Lastly, you will not save much on gas on
these nice days by driving with the windows open instead of
the a/c.  I have kept detailed mileage logs for years.  All
of the Fords I have had - at least on the highway - have
gotten better fuel mileage with the a/c running instead of
the windows open.  Modern compressor just do not require the
fuel the old compressors did.

BTW, on some vehicles, disconnecting the compressor
electrically will set a fault code in the ECM.  The ECM uses
this bit of info to control idle speed.  It also cuts out
the compressor at near full throttle to prevent overspeed
damage to the compressor and allow full engine power to the
wheels.

Good luck
Lugnut

I believe you can control that by turning your temperature control setting
down just a bit. We own Fords exclusively, and in both my '99 F350 and my
wifes '03 SportTrack and '04 Explorer, there is a mark on the temp faceplate
where the compressor goes off.

Maybe not on yours, but maybe that'll help.

Spdloader

I decided to just leave the AC system alone and not install a switch.

Thanks to everyone for all the great input.