While the maximum defrost button boosts the fan speed and blasts air, you can switch to defrost simply by selecting the up arrow for air flow.

And if you need defrost, there is likely moisture inside the car that you want to remove. Leave the air conditioner on, so that it can dehumidify.

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2007 X3 3.0si, 6 MT, Premium, White

Retired:
2008 535i, 6 MT, M Sport, Premium, Space Grey
2003 X5 3.0 Steptronic, Premium, Titanium Silver
2002 325xi 5 MT, Steel Grey
2004 Z4 3.0 Premium, Sport, SMG, Maldives Blue