http://www.ps2cho.net/downloads/MB%20CD/W124/Index/103index.html
This is the Climate Control Troubleshooting Marathon:
http://www.ps2cho.net/downloads/MB%20CD/W124/w124CD1/Program/Climate/83-604.pdf
you've got a tiny little electric fan that pulls air across the Temperature Sensor
(Near the Inside rear view mirror in the Roof of the headliner) for the HVAC system.
The Electric Fan Motor lives behind the glove box(AND "Pulls" air from
a tube connected to the Sensor in the Roof)
The Sensor fan runs whenever the key is ON and the Climate Control Console
is set to ANYTHING other than OFF.[Far Right-hand Push-button]
OR (BAD THOUGHT) your CCU [Climate Control Unit] is "on the Fritz" and not
shutting off the Main HVAC Blower Fan as it should.
IF your Main HVAC Blower is still running...
You'll be able to hear it from the front of the Windshield [with the engine OFF]@ the fresh air intakes
(@ the base of the Mono Wiper)
outside the car much more easily as a diagnostic tool.