1999 Chevrolet Express Van Owner's Manual - Page 136

yellowblue A/C: Use for normal cooling on hot days. This setting cools outside air and directs it through the instrument panel outlets. BI-LEVEL A/C: Use this setting to divide airflow between the heater floor vents and instrument panel vents. The air conditioning compressor may operate in this setting to cool the air. VENT: This setting directs air through the instrument panel vents. HEAT: This setting directs air through the heater floor vents. This setting is useful for cold weather. HEAT/DEFROST: Use this setting to divide airflow between the heater floor vents and windshield. DEFROST: This setting directs air through the windshield defroster vents. This setting is useful when you have fog or ice on the windshield. Rear Heater (Without Air Conditioning) If you have a rear heater (without rear air conditioning), the control switch is located on the instrument panel. To increase and decrease the flow of heated air to the rear floor vents, turn the thumbwheel marked REAR HEAT to the blower speed you want. The knob has three speed positions. To increase the flow of heated air, turn the thumbwheel toward HIGH. To turn the fan off, turn the switch to OFF. 3-4