Control System Outputs

Air Management Doors
The air management doors are controlled by vacuum control motors and an A/C electronic door actuator motor. The air inlet and distribution doors are controlled by a vacuum control motor. The temperature blend door is controlled by the A/C electronic door actuator motor.

The A/C electronic door actuator motor provides a variable number of temperature blend door positions. The temperature control position energizes the A/C electronic door actuator motor moving the temperature blend door.

Vacuum control motors are used on both air distribution and air inlet doors. The air inlet and panel/defrost doors use a two position vacuum control motor. The floor duct/panel door uses a three position vacuum control motor. Vacuum control motors are controlled by engine vacuum through the climate control head.

Blower Motor Circuit
The blower motor circuit consists of a blower motor switch, a heater blower motor switch resistor with a thermal limiter, and the blower motor.

Blower motor speed is determined by changing the current flow to the blower motor using resistors. The blower motor switch has four speeds that are obtained using three resistors that are wired in series. The heater blower motor switch resistor is wired into the blower motor ground circuit.
^ High Speed Current through the blower motor bypasses all resistors and travels directly to ground.
^ Medium High Speed - Current travels through one resistor and then to ground reducing current flow and blower motor speed.
^ Medium Low Speed - Current travels through two resistors reducing current flow and blower motor speed.
^ Low Speed - Current flow travels through all three resistors adding the highest resistance, causing the blower motor to run at its slowest speed.

The thermal limiter is integral to the heater blower motor switch resistor and serves as a temperature protection device. The thermal limiter is wired in series with the heater blower motor switch resistor and opens when the resistor reaches approximately 121°C (250°F). When the thermal limiter opens, the blower motor will only operate on high speed. The thermal limiter does not reset; once opened, the heater blower motor switch resistor must be replaced.