On 16/04/2013 6:22 PM, R. Mark Clayton wrote:
> Lets try this again shall we. On all five 7 series I have had the AC will
> not operate below an outside ambient of 2.5C, even if the "defogger" is
> selected, UNLESS you select recirculation and even then the intake air has
> to reach 2.5C.

"A defogger, demister, or defroster is a system to clear condensation
and thaw frost from the windshield, backglass, and/or side windows of a
motor vehicle. For primary defogging, heat is generally provided by the
vehicle's engine coolant via the heater core; fresh air is blown through
the heater core and then ducted to and distributed over the interior
surface of the windshield by a blower. This air is in many cases first
dehumidified by passing it through the vehicle's operating air
conditioning evaporator. Such dehumidification makes the defogger more
effective and faster, for the dried air has a greater capacity to absorb
water from the glass at which it is directed."

http://en.wikipedia.org/wiki/Defogger

"The defroster works two ways: first, it blows warm air on the
windshield, this warm air can hold more water, so some of the water
evaporates back off of the windshield. with luck the defroster can pick
water up faster than it condenses. In a car with Air Conditioning, the
air conditioner also has a component that dehumidifies (sucks the water
out of) the air that comes out of the vents. so those cars blow warm
dry air across the windshield to draw more condensation off of the
windshield."

http://askville.amazon.com/Car-defro...uestId=7135625

Yousuf Khan