K Tahoe 4WD V8-4.8L VIN V (2000)
Housing Assembly HVAC: Description and Operation
Heating, Ventilation and Air Conditioning
Air Distribution System Description
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:
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Upper Mode
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Bi-Level Mode
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Lower Mode
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Defog Mode
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Defrost Mode
Heater Description - Auxiliary
AUXILIARY HEATER
An optional auxiliary heater supplies heat to the vehicle. The unit operates independently of the standard heater. The control on the instrument panel
regulates the unit. The system consists of a separate heater core and the blower fan.
The heater hoses extend from the unit to a vacuum operated water valve. The hoses connect to the standard heater hoses.
A 3 position vacuum operated water valve cuts off the coolant flow in the OFF position. The water valve eliminates radiant heat, and reduces the
coolant flow in the LO and MED positions.
BLOWER SPEED CONTROL-AUXILIARY
The 3-speed blower switch provides the following settings:
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LO
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MED
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HIGH
The blower motor switch is located in the instrument panel, above the radio. The blower motor switch also triggers an electro-mechanical valve to
control coolant flow to the auxiliary heater core.
In the LO speed position, the circuit continues through the heater wiring harness to 2 resistors in the blower motor resistor relay.
In the MED speed position, the circuit continues through the heater wiring harness to 1 resistor in the blower motor resistor relay.
In the HIGH speed position, the circuit continues through the heater wiring harness to the blower motor resistor relay, and closes the relay's normally
open contact. This provides full power to the blower motor from the HVAC MaxiFuse(R).
Heater System Description
The heater system provides heating, ram air, power ventilation, and the windshield defrosting. The blower fan draws outside air from the plenum at the
base of the windshield into the heater module. The forward movement of the vehicle forces additional outside air, or ram air, into the heater module.
Within the heater module, the air is heated. The heated air is routed through the ducts to the proper outlets for discharge into the passenger compartment.
A control assembly in the instrument panel allows the operator to control the blower speed, the mode of operation, and the temperature of the air coming
from the heater system.
