Leaving it in the neutral position, with automatic climate control set, it is supposed to get hot or cold, the same as the other vents do, to adjust the temperature to the setting you have selected.

Glad it helped. And no, I am not berating you, your post was very similar to other poster's who have wished the control wasn't even there.

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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