GMC 2006 Envoy Owner's Manual page 174

Turn the knobs on the control panel to choose a fan
speed, temperature and direction of airflow.
H
(Panel): Selecting panel mode will deliver air to the
four headliner outlets.
)
(Bi-level): Selecting bi-level mode will deliver
warmer air to the second seat side floor outlets, the third
seat floor outlet, and cooler air to the headliner outlets.
6
(Floor): Selecting floor mode will deliver air to
the floor outlet located in the third seat area and the side
outlets located in the second seat areas.
3-30
If your vehicle has the rear seat audio system, press the
buttons at the bottom of the audio control panel to adjust
the fan speed, mode and temperature for the rear
passengers. The selections will be shown on the display.
z 9 y
(Fan): Press the rear fan control button with
the arrow pointing right to turn the rear climate control
on. Toggle this button to adjust the air flow speed.
To turn the rear system off, toggle the left arrow until
the display turns off.