I use the recirc most of the time in Texas, just to keep out as much pollen and dust as possible. That is a second value in the Recirc function. I do not put windows down when I start up, just let the A/C do the job and the Recirc stays on continuously in the Summer in my ML -- which is the car I use the most. I don't use recirc in my other cars most of the time.

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Ben Harrison Carter
1999 Mercedes ML320 87K
1992 Mercedes 300CE 89K
1995 Corvette 29K -- Sold Dec 09
1989 Mercedes 420SEL 99K -- (Sold 4/08)
1968 Mercedes 230S (106K) (Sold 9/06))
1976 Mercedes 450SEL 130K (Just sold - 06)
1961 Mercedes 220Sb (sold years ago)