Mercedes-Benz 190 E2.3 1985 Owner's Manual page 25

Q Press for fresh air ventilation or air conditioning.
For taking in fresh air or during air conditioner operation,
the air is directed to outlets (6) and (8). Adjust the air flow
with levers (7) and (9) respectively as desired.
( | Press to shut off air entry.
Fresh air into the vehicle is shut off. Use this button, for
example, to prevent outside odors or water from car
washes from entering the vehicle's interior. Do not drive
the vehicle with this setting for long periods with windows
and sliding roof closed since the vehicle's normal interior
airflow will be disrupted.