GMC 2004 Yukon XL Owner's Manual page 188

If you select recirculation while in defrost, defog or floor,
the light in the button will flash and then go out to let
you know that this is not allowed. This is normal
and helps to prevent fogging.
When the weather is cool or damp, operating the
system in recirculation for extended periods of time may
cause fogging of the vehicle's windows. To clear the
fog, select either defog or front defrost.
You may also notice that the A/C compressor will run
while in recirculation mode. This is normal and helps to
prevent fogging.
9 (Off): Press this button to turn off the entire climate
control system. Outside air will still enter the vehicle,
and will be directed to the floor. This direction can
be changed by pressing the mode button. The
temperature can also be adjusted using either
temperature knob. Press the up or down arrows on
the fan switch, the defrost button, the AUTO button,
or the air conditioning button to turn the system on when
it is off.
3-30
Display
If you press the MODE button to select an air delivery
mode, the display will change to show you the selected
air delivery mode. After ten seconds, the display will
change to show the driver temperature setting and the
selected mode.
If you press the up or down arrows on the fan switch,
the display will change to show the selected fan speed.
After ten seconds, the display will change to show
the driver temperature setting and the selected mode.
Whenever you press AUTO, the display will change
to show the following:
•
The current driver's set temperature and an arrow
for five seconds
•
The current passenger's set temperature setting
and an arrow for five seconds
•
The automatic air delivery mode and fan speed
If the driver's and passenger's temperature settings are
the same when AUTO is pressed, the temperature
setting and both arrows will be displayed for five
seconds along with the automatic air delivery mode and
fan speed. After the five second update, the display
will change to show the temperature setting, both arrows
and AUTO.