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Old 02-02-2013, 04:07 PM
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K-A K-A is offline
Location: U.S
Join Date: Nov 2010
Posts: 3,883
Mein Auto: Porsche Macan S SportDsgn
Originally Posted by markl53 View Post
Even though the "AC", or snowflake, button is lit, the system will not run the compressor below a certain ambient temperature. You can leave the button "on" all the time. Also, in heating season, the air can be moist, causing windows to fog. Leaving the compressor engaged will dry the air and avoid window fogging, even without the use of the defogger setting for heavy windshield fog. In fact, I never run the defrost function specifically, never find the need. In some fog-producing weather, I do take manual control of the fan, and possibly air distribution mode (floor + windshield), to ensure sufficient air movement in the cabin to keep the windows clear. Don't you often see cars with fogged windows in cold weather? Actually, more often than not, they are "lower class" cars that I notice. The drivers obviously don't know to turn on their compressor even when using heat. Another observation you may not have noticed on many climate systems -- as the cabin temperature moderates in cooler weather, the air delivery vents usually switch automatically to floor/windshield to deliver some cooler air toward the upper part of the cabin. By using the windshield vents, the system can avoid blowing cool air directly at the occupants while maintaining an overall comfortable setting.

However, if you are doing the fresh air "vent" thing, then yes, I turn off the snowflake. In that case I usually go to full manual to avoid the fan blowing faster and faster, trying to cool the car (if it's hot outside).
Great info. Okay, so the system is smart enough to know when to apply the compressor even when A/C is on, good to know. So you guys are saying that on a BMW, having the compressor on at all times robs absolutely NO power and MPG (like it does on pretty much any "normal car")?

Oh, and what does the "A" and "M" mean on the air-recycle button. I figure "Auto" and "Manual", but does it basically mean that it'll figure out for itself when to recycle the cabins air (as opposed to bringing in outside air) if you have it clicked to "A"?
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