It could be your blower motor for the HVAC system going out.

It is located under the cowl where the windshield wipers are.

There is also a small fan, called an aspirator motor, that is located behind the right ac vent. It's purpose is to blow air up through the A pillar, through the head liner, to the small vent opening near the sunroof control above the windshield. There is an air temp sensor there for the HVAC control to tell it what the temp is.

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Paul S.

2001 E430, Bourdeaux Red, Oyster interior.
79,200 miles.

1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".