ELECTRONIC AUTOMATIC TEMPERATURE CONTROL (EATC) MODULE
The EATC module is part of the climate control panel, which consists of temperature selection buttons, digital display window, system and rear fan on-off buttons, AUTOMATIC button, blower speed control thumbwheel, and mode control (manual override) buttons.
EATC system can be operated in full automatic mode by pressing AUTOMATIC button, or system can be manually operated by selecting one of following mode control (manual override) buttons: MAX A/C, VENT, PNL-FLR, FLOOR, FLR-DEF and DEF. (Scheme 10)
Pressing button sets EATC system in full automatic mode. The set temperature will be shown in the EATC display window. System maintains set temperature by controlling airflow direction, airflow quantity and discharge temperature required for comfort.
If warm air discharge is requested during cold weather, blower motor will remain off until engine is warm enough to provide warm discharge air. If maximum cooling is required, EATC system will automatically recirculate air inside vehicle, and then as vehicle interior approaches set temperature, it will automatically switch to outside air. (Scheme 11)
In MAX A/C mode, air inside vehicle will be recirculated to provide maximum cooling. Blower will operate at high speed, and 60 MAX A/C will be shown in display window.
In A/C mode, air inlet door is at no vacuum, admitting outside air. Heater water control valve is open, allowing hot coolant to heater core. Temperature is set manually. Compressor is engaged. Blower will operate with manual speed settings.
In VENT mode, outside air will be directed through instrument panel registers. VENT will be shown in display window. Compressor clutch will be off.
In OFF mode, air inlet door is at full vacuum, closing off outside air. Heater water control valve is closed, blocking hot coolant to heater core. Floor/panel and panel/defrost doors are at full vacuum, closing off air outlet from panel vents. Compressor is not engaged. Blower will not operate.
In PNL-FLR mode, airflow is equally distributed between panel and floor vents. PNL FLR will be shown in vacuum fluorescent display window.
In FLOOR mode, most air will be directed to floor outlets, with a small amount going to side window demisters and defrost nozzle. FLR will be shown in display window.
In FLR-DEF mode, most air will be equally distributed between defrost nozzle and floor duct outlets. A small volume of air will be bled to side window demisters. FLR and defrost symbol will be shown in display window.
In DEF mode, most incoming air is directed to defrost nozzle, with a small amount going to side window demisters and floor duct outlets. Defrost symbol will be shown in display window.
Blower Speed Thumbwheel
Rotating thumbwheel more than 10 degrees will provide manual control of blower speed. Rotating thumbwheel fully downward will lock blower speed in slowest speed. Rotating thumbwheel fully upward will lock blower speed in fastest speed. Pushing AUTOMATIC button will resume automatic operation.
Pressing button shuts off EATC system.
Pressing button shuts off rear blower operation. REAR FAN OFF will be shown in display window. Press button again to allow rear blower operation.
Buttons allow desired in-vehicle temperature selection. Pressing Red (warm temp.) button increases temperature setting in one-degree increments up to 85°F (29°C), with a final jump to 90°F (32°C) for maximum heating. Pressing Blue (cool temp.) button decreases temperature setting in one-degree decrements to 65°F (18°C), with a final jump to 60°F (16°C) for maximum cooling.
Scheme 10
Scheme 11
BLOWER MOTOR CIRCUIT
| CAUTION | The blower speed controller is cooled by air flowing through the system. DO NOT operate system with blower motor disconnected, as blower speed controller may be damaged. |
Blower Motor
Power to blower motor is controlled by a normally open blower motor relay, located in auxiliary relay box No. 2. When ignition is on, blower motor relay is energized, providing power to blower motor. The blower motor ground circuit is controlled by blower speed controller.
Blower Speed Controller (BSC)
The BSC varies blower motor speed by varying resistance in blower motor ground circuit. The EATC module sends a varying voltage signal to a power transistor in BSC. (Scheme 12) Current flows through the blower motor and power transistor to ground. BSC has delay function to gradually increase and decrease blower motor speed. A high-speed blower relay, integral with BSC, provides power for maximum blower speed.
Scheme 12
Wide Open Throttle (WOT) A/C Relay
Relay is located in power distribution box and is controlled by the Powertrain Control Module (PCM). Under certain conditions (such as engine starting, heavy acceleration, etc.), PCM will signal WOT A/C relay to interrupt power supply to compressor clutch.
A/C Cycling Switch (ACCS)
Switch is mounted on a Schrader-valve on suction accumulator-drier. If low-side pressure decreases to about 24 psi (1.7 kg/cm 2 ), switch opens, interrupting power to compressor clutch. When pressure increases to about 43.5 psi (3.06 kg/cm 2 ), switch closes, providing power to compressor clutch.
A/C Pressure Cut-Off Switch
Switch is located at compressor, on manifold and tube assembly. Switch is designed to interrupt compressor operation in the event of excessively high operating pressure. Switch is normally closed and will open if high side pressure increases to about 430 psi (30.2 kg/cm 2 ). When pressure decreases to about 260 psi (18.3 kg/cm 2 ), switch closes.
Electric Actuator (Temperature Blend Door)
Temperature blend door is controlled by an electric actuator (motor). The actuator is located on top of A/C evaporator housing. Temperature blend door actuator contains a reversible electric motor and a potentiometer. The potentiometer provides blend door position feedback to EATC module.
Vacuum Actuators
Three vacuum actuators control movement of air distribution doors. The floor/panel door actuator and panel/defrost door actuator are mounted on the A/C-heater plenum chamber. The fresh/recirculated air door actuator is located on the intake unit and controls the fresh/recirculated air door.
Fixed Orifice Tube
Fixed orifice tube is located in the liquid line, between the condenser and the evaporator. The tube creates a restriction in the high side pressure line, metering liquid refrigerant into the evaporator core. A filter screen at each end of the tube prevents the tube's orifice from clogging. The "O" rings prevent liquid refrigerant from by-passing the tube.
Pressure Relief Valve
Pressure relief valve, located in high pressure hose (near compressor), protects refrigerant system from excessive pressure. If high side pressure exceeds 450 psi (31.6 kg/cm 2 ), valve opens, venting refrigerant to atmosphere. After excessive pressure is relieved, valve closes to prevent total loss of refrigerant.
Ambient Temperature Sensor
Sensor contains a thermistor, which measures outside air temperature and sends a signal to the EATC system. Sensor is located in front of the condenser core, on left side of vehicle.
In-Vehicle Temperature Sensor
Sensor contains a thermistor, which measures temperature within vehicle and sends a signal to the EATC system. Sensor is located behind the instrument panel, above glove box.
Sunload Sensor
Sensor contains a photovoltaic (sunlight sensitive) diode, which monitors sunlight intensity within the vehicle and sends a signal to the EATC system. Sensor is located on right side of instrument panel, near defrost grille.
* PLEASE READ FIRST *
| WARNING | To avoid injury from accidental air bag deployment, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. |
EATC module self-diagnostic test will detect problems in system control functions. It will display hard DTCs and intermittent DTCs during system operation.
Note. If EATC module cannot be accessed by NGS Tester, go to TEST A . Or, if EATC module self-diagnostic test will not detect concerns associated with DLC messages, an NGS tester will have to be used to retrieve these messages.
No Communication With Eatc Module
Go to TEST A .
Improper/Erratic Airflow From Outlets
Go to TEST C .
Insufficient, Erratic Or No Heat
Go to TEST D .
A/C Does Not Operate/Does Not Operate Properly
Go to TEST E .
A/C Is Always On
Go to TEST F .
Insufficient A/C Cooling
Go to TEST G .
Blower Motor Does Not Operate
Go to TEST H .
Blower Motor Operates Continuously In High Speed
Go to TEST J .
Temperature Set Point Does Not Repeat After Turning Ignition Off
Go to TEST L .
Temperature Display Will Not Switch Between Fahrenheit & Celsius
Go to TEST M .
Go to TEST N .
Console Blower Motor Does Not Operate
Go to TEST O .
Panel/Floor Switch Does Not Operate; Console Blower Does Operate
Go to TEST P .
| WARNING | To avoid injury from accidental air bag deployment, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. |
A/C SYSTEM PERFORMANCE
- Park vehicle out of direct sunlight. Allow interior vehicle temperature to stabilize at 70-80°F (21-27°C). Connect manifold gauge set. Start engine. Select MAX A/C mode. Set blower motor on high speed setting.
- Insert thermometer in center panel vent to measure outlet air temperature. Close doors and windows. Run engine at 1500 RPM for 10 minutes.
- A/C system is okay if outlet air temperature is about 37-47°F (2-10°C) and refrigerant pressures are as specified. See «A/C SYSTEM PERFORMANCE PRESSURE SPECIFICATIONS»(ref-40041-S06077542552001011200000) table.
| Ambient Air Temp. °F (°C) | High Pressure psi (kg/cm 2 ) | Low Pressure psi (kg/cm 2 ) |
|---|---|---|
| 60 (16) | 110-200 (7.7-14.1) | 20-50 (1.4-3.5) |
| 70 (21) | 135-225 (9.5-15.8) | 20-50 (1.4-3.5) |
| 80 (27) | 160-250 (11.2-17.6) | 20-50 (1.4-3.5) |
| 90 (32) | 185-275 (13.0-19.3) | 20-50 (1.4-3.5) |
| 100 (38) | 200-290 (14.1-20.4) | 20-50 (1.4-3.5) |
A/C SYSTEM PERFORMANCE PRESSURE SPECIFICATIONS
| WARNING | To avoid injury from accidental air bag deployment, read and carefully follow all SERVICE PRECAUTIONS and DISABLING & ACTIVATING AIR BAG SYSTEM procedures in AIR BAG RESTRAINT SYSTEM article. |
Note. For removal and installation procedures not covered in this article, see A/C-HEATER SYSTEM - MANUAL article.
| WARNING | Cooling fins on BSC may be very hot. |