What could this sound be?
 

Hello,

For the last few cold days (below 39F) I have noticed a fan like sound coming from my right front dash vent. I tried the heater motor at different speeds, but the sound remains constant. As she starts to warm up the sound flutters a little, then completely goes away. Does this mean a repair down the road? Thanks for reading this.

Hugh, Sr.
1984 190d 2.2 (waiting on insurance company to fix left front fender - Allied Van Line truck didn't swing out far enough when he made the turn toward Carthage, Tennessee)

Could that be noise from the fan clutch? {does a 190 even have a cooling fan/viscous clutch?}

By fan noise do you mean rushing air or a motor running? Is it a new noise, or is it something that started when the outside temperatures got lower?

You may have some vacuum operated gizmos connected to the vent line and one of the actuators may be hissing until the engine temperature rises enough to change the climate control system command to that flapper. In my 1998 E300D TurboDiesel I get a number of such noises as things reposition themselves while I wait for the glow light to go off on a cold morning.

Not sure I would get too worried about it, yet. Jim

sounds exactly like a bad aspirator motor, this is the little fan that intakes air for the in car temp sensor, i have seen a few go bad and do what you describe.

The 2.2 has an electromagnetic clutch like an A/C compressor.

I'm not sure if your car has the cabin air temp sampler, that sends the heat to the porcupine, to adjust the fan speed, like the 124 does. If it does, that could be making noise. It is located under the passenger side dash in the 124. Mine will make noise when it is really cold. I did lube it with some ATF (as GSXR suggested) that seemed to help.

Does that make sense? Same thing Carson suggest hours ago.:D