GMC 2002 Sierra - Manual (Page 208)

3-5
The auto recirculation feature will activate when the
following are true:
D The air conditioning system is activated,
D the outside air button is on, and
D the vehicle load is high due to city traffic, extended
idling or hot weather.
The system will automatically switch to the recirculation
mode to lower the system load and improve interior
comfort. The outside air and recirculation button LEDs
will not change. The system will return to the outside air
function when the system load is reduced.
A/C (Air Conditioning): Press this button to turn
the air conditioning on and off. The system will cool and
dehumidify the air inside the vehicle when the A/C light
is on.
Air conditioning will be automatically disabled when
the outside temperature drops below a level at which
air conditioning is effective.
Electronic Climate Control System
(If Equipped)
Fan Control
The knob on the left side of the electronic climate
control panel operates the fan speed. To manually
increase airflow, move the knob clockwise. To manually
decrease airflow, move it counterclockwise.
OFF: If the knob is in OFF, outside air will still enter
the vehicle, and will be directed based on the position of
the mode knob.