I have never
understood the reason for it. Maybe they have Freon cooled carburetors or
something. :-)


You joke about the Freon, but you have come pretty close to the answer.
The reason air conditioners work is because of evaporation. The Freon
is compressed into a liquid. The condenser, the 'radiator' up front,
does serves two purposes. 1, it condenses the compressed freon gass
into liquid; and 2, it cools down the hot liquid freon. Then the liquid
is sprayed through an expansion valve into a low pressure "evaporator".
The evaporating freon cools simply through the act of evaporating.
Take a spray bottle filled with water and spray it at your face on a hot
day. The evaporating water will cool your face.

You mentioned that a carburetor can freeze even on 100 degree days. A
refrigerator can also create ice even on a 100 degree day. Much like
the freon, your gas is being sprayed into a low pressure area of the
carburator and the evaporation of the gas can cool the surrounding air,
and humidity, to a temperature below freezing.

I once knew the physics numbers behind evaporating gas, but that was
many years ago. Suffice it to say, icing can occur on hot days.