Electronic Climate Control

DESCRIPTION AND OPERATION

EATC System Diagram:

Inputs
With the use of a microcomputer, the control assembly analyzes inputs from five major sources:
1. Temperature, function, and blower selections (made by the vehicle occupants).
2. The in-vehicle temperature.
3. The ambient temperature.
4. The temperature control lockout valve and switch.
5. The A/C sunload sensor.

Outputs
Using the inputs, the microcomputer determines the correct conditions for the following six outputs:
1. The A/C clutch engagement,
2. The blower speed.
3. The A/C air temperature control door position.
4. The heater air damper door position.
5. The windshield defroster door position.
6. The heater and A/C air inlet duct door position.

Actuators

System Response Chart:

^ A small DC electric motor is used to operate the A/C air temperature control door.
^ Vacuum control motors are used to control each of the three remaining air distribution doors.
^ A feedback circuit is used in the A/C electronic door actuator motor to supply the control assembly with the A/C air temperature control door position information.
^ The blower motor is controlled by the control assembly through the A/C blower motor speed control.
^ The A/C blower motor speed control is necessary to react to the low power signal from the control assembly to provide a high power signal required to drive the blower motor. The System Response Chart shows the control assembly response to the function selections.

A Self Diagnostics feature has been included in the control assembly to supply the technician with air distribution error codes. These codes direct the technician to the damaged component.

Control Assembly

EATC Control Assembly:

The EATC control assembly is located in the instrument panel and has:
^ 11 push buttons.
^ A variable blower speed control knob for manual input.
^ A Vacuum Fluorescent Display (VFD) for displaying the set temperature, the ambient temperature, the function, and the diagnostic codes.

When the system is operating under AUTOMATIC control, the VFD display will show the preferred or target temperature to which the elements of the automatic control system respond.
^ The A/C blower motor speed, under automatic control, varies in response to the ambient temperature changes and a predetermined delay factor.
^ The temperature selection may be increased or decreased in one degree increments between 18° C (65° F) and 29° C (85° F) by pressing the red button to increase or the blue button to decrease the desired temperature. The system will respond accordingly.

Other control assembly features include:
^ A 16° C (60° F) setting for maximum cool and a 32° C (90° F) setting for maximum heat.
^ An OUTSIDE TEMP button which, when pressed, will display the air temperature outside the vehicle for four seconds.
^ An OFF button which, if pressed, will apply vacuum to close the A/C air inlet duct door, shut off the A/C blower motor operation, and discontinue the climate control functions through the system.

When the thumbwheel control for the blower motor is rotated out of the position it occupied under the automatic control, it will remain under manual control until the automatic button is pressed.
^ Under automatic control, the A/C blower motor speed varies as required to accommodate the total automatic functions in the system.
^ Under manual control, the A/C blower motor speed is constant based on the thumbwheel setting.

An illumination bulb in the control assembly provides backlighting for the VFD window. When the rheostat on the headlamp/parking lamp switch is rotated, the intensity of the light from this bulb will increase or decrease depending upon the direction of rotation. (The backlighting on the control assembly, as well as in other instrument panel locations, will dim whenever the light switch is engaged.)

SYSTEM OPERATION
The electronic climate control system automatically maintains the temperature selected for driving comfort and regulates the airflow between the:
^ A/C registers.
^ Heater outlet floor ducts.
^ Windshield defroster hose nozzle.
^ A/C side window demister and hoses.

Control Head Operational Diagram:

^ The system also provides the option of manually overriding the A/C blower motor speed and/or airflow direction as desired.
^ Additionally, the system has automatic solar compensation for high sunload conditions. The A/C sunload sensor is located in the upper LH corner of the instrument panel.
^ The outside temperature can also be displayed at any time by momentarily pressing the OUTSIDE TEMP button. The outside temperature will then be displayed for four seconds.
^ For optimum automatic operation, the system should be in AUTO mode and set to the desired temperature setting.
^ If the passenger compartment temperature is warmer or cooler than the set temperature, the climate control system will automatically provide heat (when the engine is warm) or air conditioning, as required, to reach the comfort setting as fast as possible.
^ If it is necessary to adjust the comfort setting, the setting should be changed only in small increments 1-2 degrees to maintain comfort and to avoid large variations of the passenger compartment temperature. Raising or lowering the set temperature in large increments from the comfort setting will not reduce the time required to reach stabilized comfort.

AUTOMATIC
Press the AUTOMATIC button to turn the system ON for fully automatic operation. When functioning automatically, the VFD window will be lighted to show the selected temperature. The system will maintain this temperature by controlling airflow direction (functional setting), airflow quantity (fan speed), and discharge temperature required for comfort.
^ When heating is required, airflow will automatically be directed through the heater outlet floor ducts and the A/C side window demister and hoses with a small amount of air through the windshield defroster hose nozzle. During cool weather, fan operation will be delayed until the engine has heated sufficiently to provide warm discharge temperatures.
^ When cooling is required, the airflow will be directed through the instrument panel registers. The A/C registers can be adjusted for optimum comfort. When maximum cooling is required, the system will automatically operate with recirculated air for rapid cool-down and automatically change to outside air as the passenger compartment interior approaches the selected temperature.
^ In moderate conditions, the system will automatically operate in a split mode, with airflow directed through the heater outlet floor duct and through the windshield defroster hose nozzle at a moderate temperature and fan speed.

OFF
Press the OFF button to turn the system OFF completely; OFF will appear in the digital display window.

DIGITAL DISPLAY WINDOW
The digital display window will indicate one of three displays depending upon the manual selection:
1. The selected comfort temperature.
2. The outside temperature.
3. OFF when the system is off.

WARMER (RED) BUTTON
Press the red button to raise the temperature setting. Press the button once to raise the temperature one degree. Holding the button in will continuously raise the temperature setting in one-degree increments to 29° C (85° F), and then will jump to 32° C (90° F) in one step for continuous maximum heating.

COOLER (BLUE) BUTTON
Press the blue button to lower the temperature setting. Press the button once to lower the temperature one degree Holding the button in will continuously reduce the temperature setting in one-degree increments to 18° C (65° F) and then will jump to 15° C (60° F) in one step for continuous maximum cooling.

OUTSIDE TEMP
Press this button to display the outside temperature for four seconds.Then the display will automatically change back to the previous setting. Outside temperature may be selected any time the ignition switch is in the RUN position whether the system is ON or OFF.

MANUAL OVERRIDES
There are six manual override buttons along the lower edge of the control assembly. Each affects the system operation as follows:

MAX A/C
Depressing the MAX A/C button will display "60 MAX A/C" in the display window. The system will go to high blower with a maximum cool discharge temperature while also going into the recirculation function.

VENT
Pressing the VENT button will display "VENT" in the display window. The system will operate with fresh air in the panel function. The A/C clutch will be turned OFF.

PNL/FLR
Pressing the PNL-FLR button will display "PANEL FLOOR" in the display window. The air will be discharged equally between the panel and the floor. The A/C clutch will be ON.

FLOOR
Pressing the FLOOR button will display "FLOOR" in the display window. The majority of the air distribution will be directed through the heater outlet floor duct with a small bleed to the A/C side window demister and hoses and the windshield defroster hose nozzle.

FLR-DEF
Pressing the FLR DEF button will display "FLOOR DEFROST" in the display window and results in a mix position, with the air distributed equally between the windshield defroster hose nozzle and the heater outlet floor ducts with a small bleed out the A/C side window demister and hoses.

DEFROST
Pressing the DEFROST button lights the "DEFROST" indicator and directs the majority of the airflow through the windshield defroster hose nozzle with a small bleed to the A/C side window demister and hoses and the heater outlet floor ducts.

Blower Speed Override Thumbwheel
Rotate the blower speed override thumbwheel more than 10 degrees to turn OFF the AUTOMATIC blower indicator and provide manual control of the A/C blower motor speed.
^ Rotating the wheel fully down against its lower stop locks the A/C blower motor at its lowest speed.
^ Rotating the wheel fully up against the stop, locks the blower at its highest speed. Press the AUTOMATIC button to resume automatic A/C blower motor control and the AUTO A/C blower motor indicator will turn off.