Mustang GT V8-4.6L SOHC VIN X (1998)
Control Assembly: Description and Operation
The climate control assembly has three control knobs:
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The air flow control or function selector knob is a vacuum selector valve combined with an internal electrical switch.
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The temperature control knob, controls the position of the temperature control door, is mounted on A/C evaporator housing.
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The blower motor control knob is an electrical switch that provides four speeds of blower motor operation.
Air Flow Control
Air flow control is accomplished in the following manner:
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Primary control is through the function selector knob, mounted on the A/C-heater function selector switch, which is part of the heater control.
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The function selector knob has the following positions: OFF, VENT FLOOR, MIX and DEFROST.
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The A/C-heater function selector switch combines a vacuum selector valve with an internal electrical switch.
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The vacuum selector valve directs source vacuum to various vacuum control motors. Refer to the system Airflow Schematic and Vacuum
Control Chart.
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An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor
switch.
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The position of the function selector knob determines the manner in which the system will operate.
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Each position of the function selector knob is detented for positive engagement.
Temperature Control
The temperature control operates in the following manner:
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Temperature control of the heater system is determined by the position of the temperature control knob (between COOL and WARM).
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This control is accomplished by means of an A/C temperature cable that operates the A/C air temperature control door.
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Movement of the control knob from COOL to WARM causes a corresponding movement on the A/C air temperature control door and
determines the temperature that the system will maintain.
The temperature control system uses a reheat method to provide conditioned air to the passenger compartment.
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All airflow from the blower motor passes through the A/C evaporator housing.
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Temperature is then regulated by mixing the portion of the air directed through the heater core with the remaining cool air to the desired
temperature.
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Temperature blending is varied by the A/C air temperature control door, which regulates the amount of air that flows through and around the
heater core, after which it is then mixed and directed into the distribution heater air plenum chamber.
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Air is finally directed to the heater outlet floor duct, windshield defroster hose nozzle or the instrument panel A/C registers, according to the
function selector knob position.
Blower Motor Control
Blower motor operation is controlled by the heater blower motor switch.
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The heater blower motor switch provides four manually-selected blower speeds and may be operated in any position to select the desired
amount of airflow.
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The heater blower motor switch and the heater blower motor switch resistor are positioned in the ground circuit of the blower motor.
