GMC 2002 Envoy Owner's Manual page 180

To find your comfort setting, start with a 74 _ F (23 _ C)
temperature setting and allow about 20 minutes for the
system to regulate. Turn the driver's or passenger's side
temperature knob clockwise or counterclockwise to
adjust the temperature setting as necessary. If you
choose the temperature setting of 60 _ F (15 _ C), the
system will remain at the maximum cooling setting
and fan speed. If you choose the temperature setting of
90 _ F (32 _ C), the system will remain at the maximum
heat setting and fan speed. Choosing either maximum
setting will not cause the system to heat or cool any
faster.
Be careful not to cover the sensor located on the top of
the instrument panel near the windshield. This sensor
regulates air temperature based on sun load, and also
turns on your headlamps.
The EXT (exterior) temperature sensor is located in the
front of the vehicle behind the grille. The displayed
temperature is most accurate after the vehicle has been
moving for a few minutes. If the vehicle is stopped and
then restarted within 2 1/2 hours, the sensor will be hot
from the engine heat. In this case, the temperature first
displayed will continue to be the temperature that was
displayed before the vehicle was turned off. The display
will update after the vehicle has been moving for a few
minutes and the sensor has a chance to cool down to the
actual temperature.
3-6
To avoid blowing cold air in cold weather, the system
will delay turning on the fan until warm air is available.
The length of delay depends on the engine coolant
temperature. Pushing the fan switch will override this
delay and change the fan to a selected speed.
Manual Operation
You may manually adjust the air delivery mode or fan
speed. Use the mode button to cycle through the
following four air delivery modes:
(Panel): This setting will deliver air to the
instrument panel outlets.
-
(Bi Level): This setting will deliver warmer air to
the floor and cooler air to the instrument panel outlets.
(Floor): This setting will deliver air to the
floor outlets.
(Defog): This setting will deliver air to the floor
and windshield outlets.
OFF: Press this button to turn the system off. Some
fresh air will continue to flow through the vehicle from
the floor outlets. The system will try to maintain the
previously chosen temperature setting.