Oldsmobile 1998 Aurora Owner's Manual page 158

Rotate the control between the rear outlets up to direct
air through the upper outlets. Rotate the control down to
direct air through the lower outlets. Adjust the direction
of aifflow from side to side with the controls in
each outlet.
Ventilation Tips
Keep the hood and front air inlet area between the
base of the windshield and the hood free of ice,
snow, or any other obstruction (such as leaves). The
defroster and heater will work far better, reducing
the chance of fogging the inside of your windows if
this area is clear.
Keep the air path under the front seats clear of
objects. This helps air to circulate throughout
your vehicle.
3-8