Express 1/2 Ton Van V6-4.3L VIN W (1999)
When the temperature knob in the control assembly is at the extreme left side of travel, the full BLUE, or cold position, the temperature valve stops all
the airflow through the heater core. The heater duct and the defroster nozzle receive only unheated air.
When the temperature knob moves away from the full BLUE, or cold position, the temperature valve opens to allow an increasing amount of air to pass
through the heater core. At the same time, the temperature valve reduces the amount of unheated air that enters into the mixture. The result is a very
responsive control of the temperature of the air discharged through the heater ducts and the defroster nozzle.
When the temperature knob reaches the full RED, or hot position, to the extreme right end of travel, the temperature valve diverts all the airflow through
the heater core for maximum heating.
Hot coolant from the engine moves through the heater core and returns to the cooling system when the engine is running.
