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Old 01-13-2010, 07:51 PM   #9 (permalink)
busypaws
EcoModding Apprentice
 
Join Date: Jul 2009
Location: Live in Tucson AZ, work and car now in Detroit
Posts: 200

Protege - '97 Mazda Protege DX
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Just to make sure there are no misunderstandings. There have been many discussions on some of the forums here about A/C on or off when you are in a defrost situation. I just want to make sure your on the same page.

Most defrosters have two functions. Move the warm air up onto the glass to warm the glass so the moisture that is in the air does not condense on the glass and fog it up.
To make the defroster work faster most vehicles kick on the A/C when you are in defrost. The A/C removes some of moisture in the air making it less likely that moisture will condense on the glass. All A/C's pump cold air into the cabin and water out of the cabin. (that's the water dripping out under the car when the A/C is on)
So if you put all the vent/airflow parts back together properly you still get the warm air flowing up on the glass you just won't get the "Dry out the air" part of the A/C when on maximum defrost.
What this means is that if you're looking to melt ice on the outside of the glass there will be no effect. (Your still have to wait for engine to warm up so you get warm air). Removing the "fog" on the inside will be slower without an A/C.
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