Try pressing the little bar between the switch halves....automatic......then drive your car and see what happens......when fan is in "Auto" mode it changes speed as the Klima Kontrol dictates......

I'm not sure which model Klima Control is in your vehicle......BUT.....MB recommends that the system be operated in the EC mode (economy) the air condition compressor will not run in this mode......I say recommends, more like recommends over the 0 mode which is off.....

When driving the vehicle.....rotate the temperature wheel from red thru white to blue, and back......slowly, a little at a time.....there is a sensor that samples inside air temperature and will adjust the fan speed as necessary (also the "monovalve").......this should tell you if the Klima is working....

On my car '85 300D...the air sensor takes air fron the center of the dash, there is a little grill close to 1" square.......I dunno about the "S Class" vehicles......someone else here, maybe "Hatteras Guy" he has a buncha "S Klasse" carz......should be able to help....

SB

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Diesels:
'85 300D, "Max, Blue Benz", 155K, 27.0 MPG
'84 190D 2.2, "Eva, Brown Benz", 142K, 40.2 MPG
'77 240D (parts car)
'67 Eicher ES 202 Tractor "Otto" (2cyl, Air Cooled, 30HP)
Gassers:
'94 Ford F-150, "Henry", 170K (300 Six) 17.5 MPG
'85 190E 2.3, 148K....Parts Car
'58 Dodge W300M Powerwagon (Flat Fenders) Less than 10 MPG