"John Carrier" > wrote in message
...
> A lot of US cars will automatically turn AC on when defrost is selected.
> This is specifically intended to dry the air prior to heating it to help
> with defog. Even if your bimmer is smart enough to turn on AC for
> temperature control (my E39 isn't ... it's surprisingly unsophisticated
for
> a $40-50K car), it probably isn't when temps are low, inside humidity high
> and there is no apparent need to turn the compressor on. SO ... manually
> select the AC while in the defrost mode and you'll rapidly clear your
> windows of fog.
>


Often times, you might want to direct airflow onto the windshield, Defrost,
but not want the AC to blow. For example, some drivers like air to flow
through the cabin, but do not like it in their face as happens through the
Vent ducts in the dashboard; these drivers might want to select the control
that sends air onto the windshield, and not condition the air in any way.

Giving you the option of running the AC or not should not be considered a
sign of unsophistication. Indeed, assuming you want the AC on simply because
you have decided to direct airflow onto the windshield is rather
unsophisticated, if you ask me.