My Euro 500SEL has the auto climate control but from what I remember from my 300CE is that this position gives you outside fresh air in the car without the blower running. Might be worth a try see if it is the same . . .

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1993 190E 2.0L (Euro.) sold
1991. 500 SEL (Euro.)
1991. 300 CE (Euro.) sold
1993. 500 E (U.S. spec.)