K 1500 Suburban 4WD V8-6.5L DSL Turbo VIN F (1999)
HEATER MODE
When the mode rotary knob is in the HEATER position, the defroster valve remains closed. As a result, the air from the blower fan receives heat.
This air goes to the defroster valve. The defroster valve sends most of the airflow to the heater duct, with some of the air going to the defroster
nozzle.
DEFROST MODE
When the mode rotary knob is in the DEFROST position, the defroster control cable moves the defroster valve in order to fully uncover the
opening to the defroster nozzle. This restricts the opening to the heater duct. This delivers the maximum airflow to the defroster, with only a small
amount of the airflow exiting out of the heater duct.
