Control Assembly, HVAC

CLIMATE CONTROL ASSEMBLY
The climate control assembly has three control knobs:
- The air flow control or function selector knob is a vacuum selector valve combined with an internal electrical switch.
- The temperature control knob, which controls the position of the A/C electronic door actuator motor is mounted on the A/C evaporator housing.
- The blower motor control knob is an electrical switch that provides four speeds of heater blower motor operation.

Air Flow Control
Air flow control is accomplished in the following manner:
- Primary control is through the function selector knob, mounted on the A/C damper door switch, which is part of the heater control.
- The function selector knob has the following positions: OFF, PANEL, PANEL/FLOOR, FLOOR, FLOOR/DEFROST and DEFROST.
- The A/C damper door switch combines a vacuum selector valve with an internal electrical switch.
- The vacuum selector valve directs source vacuum to various vacuum control motors.
- An internal single-pole electrical switch is also controlled by the selector. The switch controls the electrical supply to the heater blower motor switch.
- The position of the function selector knob determines the manner in which the system will operate.
- Each position of the function selector knob is detented for positive engagement.

Temperature Control
The temperature control operates in the following manner:
- Temperature control of the heater system is determined by the position of the temperature control knob (between COOL and WARM) of the heater control.
- This control knob is connected to a potentiometer mounted in the heater control. This potentiometer is electrically connected to the A/C electronic door actuator motor that operates the A/C air temperature control door.
- 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.

System uses a "reheat" method to provide conditioned air to the passenger compartment.
- All airflow from the blower motor passes through the A/C evaporator housing.
- Temperature is then regulated by reheating a portion of the air and blending it with the remaining cool air to the desired temperature.
- Temperature blending is varied by the A/C air temperature control door, which regulates the amount of air that flows through and/or around the heater core, where it is then mixed and distributed.

Blower Motor Control
On the manual system, heater blower motor operation is controlled by the heater blower motor switch which is part of the heater control.
- 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.
- The heater blower motor switch and the heater blower motor switch resistor are positioned in the ground circuit of the blower motor.
- The location protects the heater blower motor switch and heater blower motor switch resistor from damage if a short circuit occurs in the wiring harness by operating the blower motor to use the electrical power.