Electronic Automatic Temperature Control (EATC)

Component Locations - EATC, Part 1:

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 Control System Inputs

Climate Control Assembly
The EATC module, located in the instrument panel, has the following features:
^ a blower speed override for manual input.
^ a vacuum fluorescent display for displaying set temperature, ambient temperature, function and Diagnostic Trouble Codes (DTCs).
^ an On-Board Diagnostic (OBD) feature to supply the technician with Diagnostic Trouble Codes (DTCs). These DTCs direct the technician to the inoperative component.
^ can be switched between C° and F° display readings by pressing the MAX A/C and DEFROST buttons simultaneously for at least 1 second.

A/C Ambient Air Temperature Sensor
The A/C ambient air temperature sensor and bracket:
^ 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 EATC module.

In-Car Temperature Sensor
The in-car temperature sensor operates in the following manner
^ A thermistor in the in-car temperature sensor measures air temperature inside the passenger compartment.
^ An automatic temperature control sensor hose and elbow is connected between the plenum assembly and the in-car temperature sensor.
^ The automatic temperature control sensor hose and elbow uses air from the plenum assembly air stream to create a suction at the in-car temperature sensor.
^ The suction draws in-vehicle air into the in-car temperature sensor and across the thermistor.

A/C Sunload Sensor
The A/C sunload sensor:
^ contains a photovoltaic diode that is sensitive to light.
^ supplies the EATC module with information indicating sunload.

EATC Control System Outputs

A/C Blower Motor Speed Control
The A/C blower motor speed control is a Pulse Width Modulated (PWM) type which provides variable blower speed control of the blower motor. The A/C blower motor speed control is controlled by switching the control signal voltage of 5 volts OFF and ON 2,000 times per second. By varying the ratio of time on (+5 volts) to time off(0 volts), the EATC module tells the A/C blower motor speed control how fast the blower motor should run. The A/C blower motor speed control has the following features:
^ Has circuitry to protect the blower motor from burning out in the event of a locked rotor condition.
^ Can compensate for changes in battery positive voltage (B+) which prevents the blower speed from slowing down when the engine is idling and will provide up to a maximum of 30 amperes for blower motor operation with battery voltages between 10 and 16 volts.

Temperature Blend Door Actuator
The A/C electric blend door actuator is located on the plenum assembly.
^ Its function is to move the air temperature blend door on command from the control assembly.
^ The A/C electric 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 EATC module and is compared to the desired wiper voltage determined by the EATC module. The control module then drives the actuator motor in whichever direction is necessary to make the actuator wiper voltage agree with the desired wiper voltage.