Electronic Climate Control

Component Views Part 1 Of 2:

Component Views Part 2 Of 2:

Electronic Automatic Temperature Control (EATC)
With the use of a microcontroller, the Electronic Automatic Temperature Control (EATC) module analyzes input from the following major sources:
^ temperature, function and blower selection (made by the vehicle occupants)
^ in-vehicle temperature
^ ambient temperature
^ sunload
^ vehicle speed
^ engine coolant temperature

EATC System Response Part 1 Of 2:

EATC System Response Part 2 Of 2:

[a] The EATC activates the A/C clutch via a relay, but whether or not the A/C clutch is actually ON also depends on the position of the A/C pressure cut-off switch.

[b] If the engine coolant temperature fails to reach 50°C (122°F) after 3-1/2 minutes of operation, the blower motor speed will increase to the desired speed within the next minute and the panel/floor door will shift from the defrost position to the floor position.

Using these inputs, the microcontroller determines the correct conditions for the following outputs:
^ A/C compressor clutch engagement
^ blower speed
^ air temperature blend door position
^ panel/floor door position
^ panel/defrost door position
^ air inlet duct door position
^ outside temperature display

Floor Console Blower
The floor console blower provides airflow to the rear sear passengers. Controls for the console blower are incorporated into the rear integrated control panel located in the rear of the floor center console. The controls adjust the console blower speed and the direction of airflow. The floor console blower is not available with auxiliary air conditioning. Removal and installation of the rear integrated control panel is covered in Radio, Stereo, Compact Disc.

Control System Inputs-EATC

Climate Control Assembly
The Electronic Automatic Temperature Control (EATC) module, located in the instrument panel, has the following features:
^ 11 push buttons
^ a blower speed override thumb wheel 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.

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:
^ is located on the top of the instrument panel.
^ contains a photovoltaic diode that is sensitive to light.
^ has some unspecified resistance across the terminals depending upon the amount of light reaching the photovoltaic diode; therefore the only test that can performed is for an internal short circuit.

Control System Outputs-EATC

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.

A/C Electric 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.