There is a fan inside the HVAC control that sucks air into those little vents on the face. This is to measure the interior air temperature. There should be a thread on here for removing the control unit then removing and cleaning the fans. I think the fans are also replaceable if cleaning doesn't fix it.

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Olympic Peninsula, WA, USA
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2005 Mini Cooper 100k, British Racing Green/Silver-Black
04/2002 4.6is 140k, Silver/Black-Alcantara *FOR SALE*
1989 325iX 270k, Diamond Black/Black
1984 318i 370k *SOLD* (First Bimmer)
Honorable Mentions: '71 2002, '87 325, '90 325ic, '92 525it, '93 325i, '94 530i