Chevrolet 1998 Lumina Owner's Manual page 142

Air Conditioning
On very hot days, open the windows long enough to let
hot, inside
air
escape. This reduces the A/C compressor
load, which should help fuel economy.
For quick cool-down on very hot days, use MAX with
the temperature control all the way in the blue area. If
this setting is used for long periods of time, the air in
your vehicle may become too dry.
For normal cooling on hot days, use A/C with the
temperature control in the blue area. The system will
bring in outside air and cool it.
On cool but sunny days, the sun may warm your
upper body, but your lower body may not be warm
enough. You can use BI-LEVEL with the temperature
control in the middle. The system will bring in outside
air and direct it to your upper body, while sending
slightly warmed air to your lower body. You may
notice this temperature difference more at some times
than at others.
Heating
On cold days use FLOOR with the temperature control
all the way in the red area. The system will bring in
outside air, heat it and send it to the floor ducts.
If your vehicle has an engine coolant heater, you can use
it to help your system provide warm air faster when it's
cold outside (0°F (-18°C) or lower). An engine coolant
heater warms the coolant your engine and heating
system uses to provide heat. See "Engine Coolarg
Heater" in the Index.
Ventilation System
Adjust the direction of airflow by moving the vents.
Your vehicle's flow-through ventilation system supplies
outside air into the vehicle when it is moving. Outside
air will also enter the vehicle when the air conditioning
fan is running.