GMC 2002 Yukon XL Owner's Manual page 194

Heating
The heater works best if you keep your windows closed
while using it. On cold days, use the floor or bi
setting with the temperature knob in the red area.
On cold days, approximately 32 _ F (
your vehicle is equipped with an automatic transmission,
you may experience differences in how the transmission
shifts until the engine is warm. This feature automatically
reduces the time it takes for the engine to reach normal
operating temperature and shortens the time it takes the
heater to reach full output.
If you use the engine coolant heater before starting your
engine in cold weather, 20 _ F (
heating system will produce warmer air faster to heat the
passenger compartment.
The use of an engine coolant heater also reduces the
time it takes for the engine to reach normal operating
temperature. For more information, see "Engine Coolant
Heater" in the Index.
3-14
-
level
0 _ C) or lower, if
-
8 _ C) or lower, the
-
Defogging and Defrosting
On cool, humid days, use defrost setting to keep the
windshield and side windows clear. Use the defrost
setting to remove fog or ice from the windshield in
extremely humid or cold conditions. Use the defrost
setting with the temperature knob toward the red area
and the fan control turned all the way to the right.
Rear Window Defogger (If Equipped)
If you see lines running across the rear window, you
have a rear window defogger. The lines warm the glass.
The rear window defogger will only work if the ignition
is in RUN. For best results, clear the window of as much
snow or ice as possible.
To turn on the rear window
defogger, press this button
next to the fan knob.