Within the heater module is a series of valves called the temperature valve, the vent valve and the defroster valve. Valves are hinged components that direct airflow through the various sections of the heater module. The valves provide the proper airflow for the selected operating mode.
The Temperature Valve and The Heater Core
The temperature of the air coming from the heater duct and the defroster nozzle is regulated by controlling the relative amounts of warm and cool air coming from the heater module. The temperature valve determines the amount of the total airflow that passes through the heater core.
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.
The Mode Valves
The heater system provides the following 5 basic operating modes:
| • | Upper Mode |
| • | Bi-Level Mode |
| • | Lower Mode |
| • | Defog Mode |
| • | Defrost Mode |
