According to the parts catalog above, yours has a blower regulator http://catalog.worldpac.com/mercedesshop/sophio/wizard.jsp?partner=mercedesshop&clientid=catalog.mercedesshop&baseurl=http://catalog.peachparts.com/&cookieid=2DM1BXZHD2DM1BY3X2&year=1990&make=MB&model=420-SEL-001&category=R&part=Blower+Regulator

Not cheap. Since it returned to normal speed, it might not be the regulator - thing is, I honestly don't know what direction to point you in (sorry).

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It is a truism that almost any sect, cult, or religion will legislate its creed into law if it acquires the political power to do so. Robert A. Heinlein


09 Jetta TDI
1985 300D