Electronic Automatic Temperature Control (EATC)

CONTROL COMPONENTS - ELECTRONIC AUTOMATIC TEMPERATURE CONTROL (EATC)

With the use of a microcontroller, the remote climate control module analyzes input from the following major sources:
- Integrated control panel (temperature, air distribution and blower selection)
- in-vehicle temperature
- ambient temperature
- sunload - vehicle speed
- engine coolant temperature

Using these inputs, the microcontroller determines the correct conditions for the following outputs:
- A/C compressor operation
- blower speed
- air temperature blend door position
- airflow mode door position
- defroster door position
- air inlet door position

Control System Inputs

Integrated Control Panel
The integrated control panel (ICP) combines the audio unit and climate controls as an assembly. The ICP has the following climate control features:
- It is used to supply the remote climate control module with function/mode selection information.
- It contains a blower speed override control for manual input
- It has a vacuum fluorescent display for displaying set temperature, ambient temperature, function and diagnostic trouble codes (DTCs)

Remote Climate Control (RCC) Module
The remote climate control module is used to control the climate control system based on input from the ICP. The remote climate control module has the following features.
- It is mounted to the heater core and evaporator core housing , to the left of the blower motor.
- It communicates with the ICP using the CAN network.
- Uses an On-Board Diagnostic (OBD) feature to supply the technician with diagnostic trouble codes (DTCs). These DTCs direct the technician to the inoperative component.

Evaporator Discharge Air Temperature Sensor
The PCM determines A/C compressor clutch cycling based on input from the evaporator air discharge temperature sensor. The evaporator air discharge temperature sensor:
- maintains evaporator core temperature, and prevents icing of the evaporator core by disengaging the A/C compressor when the evaporator discharge air temperature falls below a preset level, and engaging the A/C compressor when evaporator discharge air temperature rises above a preset level.
- contains a thermistor which receives a reference voltage from the PCM. The thermistor then varies the resistance to the reference voltage based on the evaporator discharge air temperature, and returns the resulting voltage to the PCM. The PCM determines evaporator air discharge temperature based on the return voltage value.
- is located in the heater core and evaporator core housing just downstream of the evaporator airflow.

A/C Ambient Air Temperature Sensor
The A/C ambient air temperature sensor:
- is located in front of the A/C condenser core near the center of the vehicle.
- contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the RCC module.

In-Vehicle Temperature Sensor
The in-vehicle temperature sensor operates in the following manner:
- A thermistor in the in-vehicle temperature sensor measures air temperature inside the passenger compartment.
- An automatic temperature control sensor hose and elbow is connected between the A/C evaporator housing and the in-vehicle temperature sensor.
- The automatic temperature control sensor hose and elbow takes air from the A/C evaporator housing air stream to create a suction in the in-car temperature sensor.
- The suction draws in-vehicle air into the in-vehicle temperature sensor and across the thermistor.

Solar Amplifier (Sunload Sensor)
For additional information on the location and service of the solar amplifier, refer to Lighting and Horns.

Control System Outputs

A/C Blower Motor Speed Control
The A/C blower motor speed control is located under the A/C evaporator housing, near the blower motor.
- The function of the A/C blower motor speed control is to convert low power signals from the RCC module to a high current, variable ground feed for the blower motor.
- A/C blower motor speed is infinitely variable and is controlled by the RCC module software.
- A delay function provides a gradual increase or decrease in blower motor speed under all conditions.

A/C Electronic Blend Door Actuator
The A/C electronic blend door actuator is located on the rear of the A/C evaporator housing.
- Its function is to move the air temperature blend doors on command from the control assembly.
- The A/C electronic blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the air temperature blend door.
- A 5 volt signal is applied to the ends of the potentiometer. The voltage available at the wiper indicates the position of the potentiometer. The expressed value of the actuator wiper voltage is sent to the electronic automatic temperature control module and is matched with the wiper voltage of the module potentiometer. The control module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the control module wiper voltage.

Vacuum Control Motors
The vacuum control motors:
- are located on the A/C evaporator housing, air inlet duct and plenum chamber.
- direct system airflow to the vehicle interior as determined by the RCC module or manual override.