Chevrolet TrailBlazer 2007 Owner's Manual page 194

If your vehicle has the rear seat audio system, the
lower buttons are used to adjust the rear seat
climate control system. The temperature of the air
coming through the rear outlets is determined
by the front passenger's temperature setting.
194
(On/Off): Press this button to turn the rear
P
climate controls on or off.
z9 y
(Fan): Press this button to adjust the fan
speed.
z\ y
(Mode): Press this button to change the
direction of airflow (panel, bi-level or floor) to
the rear seat area.
The rear control will only turn on if the front is on
and not in defrost mode.