On Sunday, August 21, 2016 at 8:09:09 PM UTC-4, wrote:
Ron D. wrote: "in a 1972 Chevelle, the AC and Defrost was linked although it may have been possible that
at full hot, the AC got turned off. I can't remember, but i suspect not. "


I always made the simplistic assumption that the only
difference between "AC" and "Defrost" modes was the
direction the compressored air was ducted: either toward
your face and feet(AC), or out the top side of the dash
toward the windshield(Def).

A lot of owners manuals suggest a temperature setting
between "10 and 2 o'clock" when using Defrost, vs
extreme/full cold or hot, respectively, for AC or Heater.

DEFROST - when there is ice or snow on the windshield

DEFOG - When there is water on the inside of the window. The Dew point determines when this occurs. Lowering the humidity of the air increases the heat capacity of the conditioned air and raises the dew point.

It's hard to get people to use the AC and Heat at the same time especially when it's cold out and you want to get warm. From a Thermodynamic view, it doesn't work.

See, I use thermodynamics in everyday life. Hot water freezes faster than cold water does. Ice expands when cooled. Increasing surface area increases heat loss. A hat will increase body temperature significantly, A hat prevents heat loss from your head. layering clothes is important. I somewhat regulate sleeping temperature by wearing one, two or no socks to bed. A bare foot in a slipper with an air gap will be warmer than a slipper, and a tight fitting sock. Wet clothes are bad when trying to stay warm.