After reading your post last night, I experimented with my a/c today.

If I turn the dial all the way to its coldest position, the fan remains on Hi.

If I set it to a less cool temperature, really any temp less than all the way, the fan will modulate its speed.

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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".