Electronic Climate Control

There are two types of A/C systems. The main difference between these systems involve the mandatory requirement of the use of different refrigerants. The two types of A/C systems are:
1. The fixed orifice tube type system with cycling clutch using the Chlorofluorocarbon (CFC) based Refrigerant 12 (R-12).
2. The fixed orifice tube type system with cycling clutch using the Non-chlorofluorocarbon (Non-CFC) based Refrigerant 134a (R-134a).

System Block Diagram:

The Electronic Automatic Temperature Control (EATC) system is available as an option. This system is graphically represented in the System Block Diagram.

With the use of a microcomputer, the control assembly analyzes inputs from six major sources:
1. Temperature, function, and blower selections (made by the vehicle occupants).
2. In-vehicle temperature.
3. Ambient temperature.
4. Cold Engine Lock Out (CELO).
5. Sunload sensor.
6. A/C system clutch cycling pressure switch.

Using these inputs, the microcomputer determines the correct conditions for the following six outputs:
1. A/C compressor clutch engagement.
2. Blower speed.
3. Blend door position.
4. Floor-panel door position.
5. Panel-defrost door position.
6. Outside-recirculation door position.

System Response Chart:

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

CONTROL ASSEMBLY

Control Assembly:

A Self Test 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.

The EATC assembly is located in the instrument panel and consists of 10 push buttons, a variable blower speed control knob for manual input and a Vacuum Fluorescent Display (VFD) for displaying set temperature, ambient temperature, function, and 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. Blower motor speed, under automatic control, varies in response to ambient temperature changes and a predetermined delay factor. Temperature selection may be raised or lowered in one degree increments between 18° C (65° F) and 29° C (85° F) by pressing the red button to raise or the blue button to lower the desired temperature and the automatic control 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 depressed, will result in a four-second display of the air temperature outside the vehicle.
^ An OFF button which, if depressed, will apply vacuum to close the outside-recirculating air door, shut off 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 automatic control, it will remain under manual control until the automatic button is again depressed. Under automatic control, blower speed varies as required to accommodate the total automatic functions in the system. Under manual control, blower speed is constant based on the thumbwheel setting.

An illumination bulb in the control assembly provides backlighting for the Vacuum Fluorescent Display (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.)

NORMAL SYSTEM OPERATION (AUTOMATIC)
The electronic climate control system automatically maintains the temperature selected for driving comfort and regulates the airflow between the instrument panel registers, floor ducts, windshield defroster nozzle, and side window demisters. The system also provides the option of manually overriding the blower speed and/or airflow direction as desired. Additionally, the system has automatic solar compensation for high sunload conditions. The 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 depressing the OUTSIDE temperature 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 vehicle interior 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 avoid large variations of in-vehicle temperature. Raising or lowering the set temperature in large increments from the comfort setting will not reduce the time required to reach stabilized comfort.

Control Head Operational Diagram:

SYSTEM DESCRIPTION
AUTOMATIC
Depressing the AUTOMATIC button turns 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 the airflow direction (functional setting), the airflow quantity (fan speed), and the discharge temperature required for comfort.

When heating is required, the airflow will automatically be directed through the floor ducts and demisters with a small amount of air through the defroster. During cool weather, the 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 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 vehicle interior approaches the selected temperature.

In moderate conditions, the system will automatically operate in a split mode, with airflow directed through the floor ducts and through the windshield defroster ducts at a moderate temperature and fan speed.


OFF
Depressing the OFF button will turn the system off completely and display the word OFF in the digital display window.

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

RED
The red button is used 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,

BLUE
The blue button is used 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
Depressing this button will display the outside temperature for four seconds and will automatically change back to the previous display. 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 system operation as follows.
1. 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 recirculation function.
2. Vent
Depressing 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.
3. PNL/FLR
Depressing 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.
4. Floor
Depressing the FLOOR button will display "FLOOR" in the display window. The majority of the air distribution will be directed through the floor ducts with a small bleed to the side window demisters and the defroster nozzle.
5. FLR/DEF
Depressing 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 defroster nozzle and the floor ducts, with a small bleed out the side window demisters.
6. Defrost
Depressing the DEFROST button lights the "DEFROST" indicator and directs the majority of the airflow through the defroster nozzle, with a small bleed to the side window demisters and the floor ducts.

Blower Speed Override Thumbwheel
Rotating the blower speed override thumbwheel more than 10 degrees will turn on the AUTO blower indicator and provide manual control of the blower speed. Rotating the wheel fully down against its lower stop locks the blower at its lowest speed. Rotating the wheel fully up against the stop, locks the blower at its highest speed.

Depressing the AUTO button will resume automatic blower control and the AUTO blower indicator will turn off.