GMC 1996 Sierra Owner's Manual page 134

The A/C button, between the temperature and mode
knobs, allows the air coming into
your vehicle to be
cooled. This setting is useful for normal cooling on hot
days. When you
use A/C
with the recirculation button
pushed in, turn off recirculation as soon as the vehicle
reaches a comfortable interior temperature.
With the A/C on, move the temperature knob to MAX
for maximum cooling. This setting also puts the system
in the recirculation mode and helps to maximize your air
conditioner's performance and your vehicle's fuel
economy. This setting also cools the air the fastest. After
the vehicle's interior reaches a comfortable temperature,
move the temperature knob clockwise to place the air
conditioning system in the normal mode.
Heating
The heater works best if you keep your windows closed
while using it. On cold days, use
the
HEATER or
VENT/HEAT setting with the temperature knob in the
red area.
If you use the engine coolant heater before starting your
engine (in cold weather (20°F (-8°C) or lower), your
heating system will produce warmer air faster, to heat
the passenger compartment in cold weather.
The use
of an
engine coolant heater also reduces the
time
it
takes for the engine
t o
reach normal operating
temperature, and shortens the time it takes the heater to
reach full output. For more information, see "Engine
Coolant Heater" in the Index.
Ventilation System
For mild outside temperature when little heating or
cooling is needed, use VENT to direct outside air
through your vehicle. Air will flow through the
instrument panel outlets.
Your vehicle's ventilation systeril supplies outside air
to the inside of your vehicle when it is moving. With
the side windows closed, air will flow into the front
air inlet
grilles,
through
the
vehicle, and out the air
exhaust valves.
Outside air will also enter the vehicle when the heater or
the air conditioning fan is running, unless you have the
recirculation button pushed in. For more information on
the recirculation button, see "Air Conditioning" earlier
in this section.
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