Control System Outputs - Electronic Automatic Temperature Control (EATC)

NOTE: Each of the 4 control system outputs may be overridden by the passenger if desired.

When operating in AUTO mode (if equipped), the control system outputs are automatically adjusted by the HVAC control module.

Blower Motor Speed Control

The blower motor speed control controls the blower motor speed by converting low power signals from the HVAC control module to a high current, variable ground feed for the blower motor. A delay function is used to provide a gradual increase or decrease in blower motor speed under all conditions.

The blower motor speed control is located on the heater core and evaporator core housing near the blower motor.

Temperature Door Actuators

The single-zone EATC system has one temperature door actuator located on the top of the heater core and evaporator housing. The dual-zone EATC system uses 2 temperature door actuators to control 2 separate temperature doors. The temperature doors independently vary the driver side and passenger side temperature settings, as desired. The temperature door actuators each contain a reversible electric motor and a potentiometer. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a wiper which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the wiper indicates the position of the temperature door. The HVAC control module drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected HVAC control module wiper voltage value.

Mode Door Actuators

Two electric mode door actuators are used to position the 3 airflow mode doors on command from the HVAC control module. The 2 mode door actuators each contain a reversible electric motor. The DEFROST/PANEL/FLOOR mode door actuator contains a potentiometer to allow the HVAC control module to monitor the position of the airflow mode doors. The potentiometer circuit consists of a 5-volt reference signal connected to one end of a variable resistor, and a signal ground connected to the other. A signal circuit is connected to a wiper, which is driven along the variable resistor by the actuator shaft. The signal to the HVAC control module from the wiper indicates the position of the airflow mode door. The air inlet mode door actuator is driven to the full RECIRC or full FRESH air inlet position, and does not require a potentiometer circuit to monitor its position.