Chevrolet 2006 TrailBlazer EXT Owner's Manual page 171

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.
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(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.
z\ y
(Mode): Press this button to change the
direction of airflow (panel, bi-level or floor) to the rear
seat area.
zb y
(Temperature): Press this button to increase
and decrease the temperature setting.
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