GMC Cadillac CTS 2004 Owner's Manual page 154

Outlet Adjustment
Use the knobs located in the center of each outlet to
change the direction of the air flow. Use the
thumbwheels to open or close the outlets.
3-34
Use the thumbwheel on
the front outboard outlets
to select from the
following positions.
j
(Side Window Defog): Turn the thumbwheel to this
symbol to use the side window defog setting. The air
coming through the outlets will be directed toward
the side windows to clear fog.
k
(Open): Turn the thumbwheel to this symbol to
open the outlets completely and allow the maximum
amount of air to enter your vehicle. A small amount of air
will still be directed to the side windows.
l
(Closed): Turn the thumbwheel to this symbol to
close the outlets and minimize the amount of air entering
the vehicle.