HVAC System - A/C-Heater System - Manual: Operation: Notes

Air inlet and distribution doors are controlled by vacuum control motors.

The electronic door actuator motor provides a variable number of temperature blend door positions. Temperature control position energizes electronic door actuator motor, moving temperature blend door. Air temperature blend door controls amount of air directed through or around heater core to control temperature of air entering passenger compartment. It is controlled by temperature control switch. An A/C electronic door actuator motor located on top of heater air plenum chamber positions air temperature blend door to allow more or less air to pass through heater core. In full cool position, all incoming air bypasses heater core. In full warm position, all incoming air is directed through heater core.

Air inlet and panel/defrost doors use a 2 position vacuum control motor. Floor duct/panel door uses a 3 position vacuum control motor. Vacuum control motors are controlled by engine vacuum through control panel.

The vacuum system is source of power for function of mode doors. Engine vacuum is supplied to and stored in vacuum reservoir, which is located on top of right frame rail behind headlight assembly. A vacuum check valve is built into reservoir. Vacuum is routed to function control switch, vacuum motors, and heater core water control valve through a color-coded vacuum hose harness.

The blower motor is located in blower housing, which is part of plenum assembly. Motor is connected to circuit with one hard-shell connector. Blower motor resistor is located right next to blower motor and has a thermal limiter which acts as a temperature protecting fuse. If temperature of thermal limiter reaches approximately 250°F (121°C), limiter contacts open, interrupting circuit for all speeds but high. Resistor must be replaced if limiter opens.

The A/C clutch is controlled by A/C cycling switch and A/C pressure cut-off switch, which are connected in series. A/C cycling switch is mounted on accumulator-drier, and A/C pressure cut-off switch is mounted in discharge line at A/C condenser.