K 2500 Truck 4WD V8-6.5L DSL Turbo VIN S (1998)
Heater Core: Description and Operation
Temperature Valve and Heater Core
The temperature of the air coming from the air distribution duct is regulated by controlling the relative amounts of warm and cool air in the airflow
coming from the heater module. The part of the total airflow through the heater module that is allowed to pass through the heater core is governed by the
temperature valve. The temperature valve is operated by the temperature control cable, working through a lever on the temperature valve shaft. The
valve defaults to full cold with no cable attached.
When the temperature rotary knob in the control assembly is in the full COLD position, the temperature valve is positioned to stop all of the airflow
through the heater core so only unheated air is sent to the air distribution duct.
As the temperature rotary knob moves away from the full COLD position, the temperature control cable opens the temperature valve 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 is allowed to
enter the mixture. This results in a very responsive control of the air temperature discharged through the heater ducts and defroster.
When the temperature rotary knob reaches the full HOT position, the temperature control cable holds the temperature valve in a position that diverts all
of the airflow through the heater core for maximum heating.
Hot coolant from the engine is directed through the heater core and returned to the cooling system when the engine is running.
