I don't believe that heat will ever come out of the center vents - just the driver's and passenger sides to defrost the windows, and of course the floor and defrost vents.

The Germans are weird with their climate controls. My old BMWs (635, 735) would allow for cool air to vent through the center vents, but never warm air, even if the heat was turned on max. The owner's manual said that this was to allow for cool air on the driver's face to keep him/her awake.

Troy
1995 E420 86k