I had an MB C-Class that did this all the time in hot, humid weather. The air distribution was set up to always deliver a very small amount of air through the upper defrost vents to help with overall cabin circulation. I've had my 535i for two years though, and have never noticed this, nor ever checked for air coming through the upper vents when in normal "hot weather" auto air distribution.
Originally Posted by dunccfp
Simple. The air outside is warmer. You probably have the defrost vent turned on and the cold air cools the windshield and the air right around the windshield is cooler and cooler air holds less moisturer hence the condensation. Hit auto on your system and your problem will be alleviated.
Bimmerfest Supporting Member
2011 535i AT | Black Sapphire/Cinnamon | Premium | Heated Sts | Nav | Sirius | Anthracite Hdr & Trim
Prior: 2008 335i 6MT Sedan | Black Sapphire/Terra Leather | Premium | Cold | CA | OEM Alarm
Prior: 2005 330i 6MT | Black Sapphire/Sand Leather | Premium | Cold | UGO | OEM Alarm