I don't know if it's germane to an '05 CDI but the first owner of my '96 E300 (W210) had to replace the controller ("porcupine") in the climate control because the blower ran only at a very low speed. To make it worse, the new controller was not compatible with the old blower and they had to buy a new blower too, even though there was nothing wrong with the old one. Could your car have a similar situation?

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970