300E fresh air flapping noise

[jb]

My 1988 300E has a noise in the dashboard associated with the fresh air
system. If it's cold outside and I am in the economy(non air
conditioning) mode, with the thumb wheel thermostat in the heating
position, the unit works perfectly fine. that is no noise. In warm
weather and wanting just some air flow wanted with fan on, the system
makes a pulsing flap, flap, flap noise every half-second. Very annoying.
To get it to stop, I must turn the system off, ie no fan spinning. What
causes this and what's involved with fixing it? Thanks for your help
JB
88 300E
99 E55

[Roland Franzius]

Post by jb
My 1988 300E has a noise in the dashboard associated with the fresh air
system. If it's cold outside and I am in the economy(non air
conditioning) mode, with the thumb wheel thermostat in the heating
position, the unit works perfectly fine. that is no noise. In warm
weather and wanting just some air flow wanted with fan on, the system
makes a pulsing flap, flap, flap noise every half-second. Very annoying.
To get it to stop, I must turn the system off, ie no fan spinning. What
causes this and what's involved with fixing it? Thanks for your help

There are leaves inside. They become noisy in dry wheather. The car
needs an air system cleaning.

The air intake protection grid at the windshield of some types (W124,
W202 eg) are not fine enough for the fine dry olive tree leaves.