Electronic Automatic Temperature Control (EATC)

Interior Component Locations - EATC, Part 1:

Interior Component Locations - EATC, Part 2:

Exterior Component Locations EATC, Part 1:

Exterior Component Locations EATC, Part 2:

The EATC system heats or cools the vehicle interior depending on the function and temperature selected. The function selection determines heating or cooling and air distribution. The temperature blend control setting determines air temperature.

The EATC components are used to:
^ automatically determine the climate control settings based on the temperature selected and ambient conditions (AUTO mode).
^ select the air inlet source (outside or recirculated).
^ select the blower motor speed.
^ select the discharge air temperature (temperature blend).
^ select the discharge air location (defrost, panel, floor).
^ select the A/C compressor clutch operation.

EATC System Inputs
The EATC system has five control system inputs.

EATC Module
The EATC Module:
^ is located in the instrument panel.
^ has a vacuum fluorescent display for displaying set temperature, function and Diagnostic Trouble Codes (DTCs).
^ utilizes an On-Board Diagnostic (OBD) feature to supply the technician with diagnostic trouble codes (DTCs). These DTCs help direct the technician to the inoperative component.

Steering Wheel Audio/Climate Control Switch
The steering wheel audio/climate control switch:
^ is located on the right side of the steering wheel.
^ allows the driver to adjust the passenger compartment temperature setting and manually override the blower motor speed setting.

For removal and installation of the steering wheel audio/climate control switch, refer to Radio, Stereo, and Compact Disc.

Ambient Air Temperature Sensor
The ambient air temperature sensor:
^ is attached to left side of the grille opening panel to the left of the A/C condenser core.
^ contains a thermistor which measures the temperature of outside air as a resistance and sends that reading to the EATC module.

In-Car Temperature Sensor
The in-car temperature sensor:
^ is located in the instrument panel to the right of the steering column.
^ contains a thermistor which measures the in-car air temperature and sends that reading to the EATC module.
^ utilizes a venturi system with an aspirator hose running between the in-car temperature sensor and the plenum chamber.
^ Airflow through the plenum chamber creates a suction through the aspirator hose which draws air from the passenger compartment through the in-car temperature sensor.

Solar Amplifier
The solar amplifier supplies the EATC module with information indicating sunload.

EATC System Outputs
The EATC system has five control system outputs.

Automatic Temperature Control (ATC) Solenoid and Manifold
The ATC solenoid and Manifold:
^ is located in the instrument panel behind the audio unit.
^ uses solenoid-type valves to distribute vacuum to the vacuum control motors and the heater control valve based on the EATC module settings.

Blower Motor Speed Control
The blower motor speed control:
^ is located on the evaporator core housing behind the suction accumulator.
^ varies the blower motor speed and is controlled by the EATC module.
^ uses low power signals from the EATC module to control a high-current, variable ground feed to the blower motor.
^ has a delay function to provide a gradual increase or decrease in blower motor speed under all conditions.
^ controls the integral high blower speed relay which is engaged when maximum fan speed is selected.

Temperature Blend Door Actuator
The temperature blend door actuator:
^ is located on the top of the plenum chamber behind the glove compartment.
^ moves the temperature blend door on command from the EATC module.
^ contains a reversible motor and potentiometer. The potentiometer wiper is connected to the actuator output shaft and moves with the output shaft to indicate the position of the temperature blend door.
^ applies a 5 volt signal to the ends of the potentiometer. The expressed value of the actuator wiper voltage is sent to the EATC module and is matched with an expected wiper voltage value. The EATC module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the expected EATC module wiper voltage value.

Vacuum Control Motors
The two vacuum control motors:
^ are actuated by the ATC solenoid and manifold based on inputs from the EATC module.
^ position the plenum doors to direct system airflow to the vehicles interior as determined by the EATC module settings.