...sucks in cabin air for the climate control sensor to adjust the automatic air cotrol (A/C or heater) foor your car. If you disconnect it, the car won't self-destruct, but your A/C or heater won't work right. I think there is a post, in the DIY section on how to test it to see if it is working properly. but if yours is making noise, then it is time to change it.
The whining noise is really annoying. I replaced the fan in both my daughter's 300TE and in my 420SEL.
Do a search and you will find plenty of info on this issue.
1989 300TE "Alice"
1990 300CE "Sam Spade"
1991 300CE "Beowulf" RIP (06.1991 - 10.10.2007)
1998 E320 "Orson"
2002 C320 Wagon "Molly Fox"
Res non semper sunt quae esse videntur
Not in this weather!