Mercedes-Benz 2008 M-Class Operator's Manual page 133

Controls in detail
Seats
The blue indicator lamps in the switch
come on to show which ventilation level
you have selected.
Level
3 Three indicator lamps on
(highest level)
2 Two indicator lamps on
1 One indicator lamp on
(lowest level)
off No indicator lamp on
Switch on the ignition ( page 40).
132
Switching on
Press button 1 repeatedly until the
desired ventilation level is set.
i
The seat ventilation for the driver's seat is
automatically set to the highest level if activated
via summer opening feature ( page 237).
Switching off
Press button 1 repeatedly until all
indicator lamps 2 go out.