A/C COMPRESSOR CLUTCH CONTROL
A/C compressor electromagnetic clutch is activated by engine management system. ECC control module requests activation using an A/C selected signal to engine management system via low-pressure switch (pressostat). Engine management system determines when compressor should run based on this signal, engine temperature signal, accelerator position and pressure signal from pressure sensor. Low temperature switch determines when compressor is on and off.
A/C PRESSURE SWITCHES
The A/C compressor is connected in series with the low-pressure switch, high-pressure switch and safety switch. The high-pressure and safety switch cut power to the A/C compressor if pressure in the A/C high-pressure circuit becomes excessive, supplying a signal to ECM to start cooling fan.
The low-pressure switch (pressostat) turns A/C compressor on and off to maintain pressure within limits.
AIR DISTRIBUTION CONTROL
Air distribution control is based on signals from ECC control module, which controls the ventilation and floor/defroster damper motor. When set to AUT (automatic) mode, the air distribution control circuit computes air distribution based on outside (ambient) temperature, the position of driver's side temperature control dial, and engine coolant temperature.
At low outside temperatures, the ECC control module selects floor/defrost setting, with a slight amount of bi-level air if sunshine is present. If outside temperature is between 50-66°F (10-19°C), a varying degree of bi-level air is selected. At temperatures greater than 68°F (20°C), all air is directed to instrument panel vents.
The ventilation air distribution setting is selected if driver's side control panel is set for maximum cooling. The floor/defrost setting is selected if maximum heating is selected. The defrost air distribution setting is selected if engine is cold and outside and interior temperatures are also low. This changes to varying degrees of floor/defrost air distribution as engine coolant temperature increases. The transition from defroster to floor/defroster setting takes place more quickly in sunshine.
OUTSIDE TEMPERATURE SENSOR, PASSENGER COMPARTMENT TEMPERATURE SENSOR & SOLAR SENSOR
An outside temperature sensor is located in climate control unit. (Scheme 5) A passenger compartment temperature sensor with an integrated fan is located in center of instrument panel. (Scheme 6) Resistance of the air temperature sensor decreases as temperature increases. The solar sensor, located in top center of instrument panel, is a photodiode which generates a current when exposed to solar radiation. (Scheme 7)
Scheme 5
Scheme 6
Scheme 7
DAMPER MOTORS
The temperature control damper motors, recirculation damper motor and floor/defroster/ventilation damper motor are all identical. Their control range varies according to the damper being controlled.
Damper motors have a position sensor to enable the ECC control module to determine damper position, learn damper limit positions and to detect any fault in damper motor circuit. The floor/defroster/ventilation damper is operated by one motor and one linkage system.
FAN CONTROL
Fan speed is variably controlled by ECC output (power) stage in response to signals from ECC control module. The ECC control module digital control signals vary in length according to required fan speed.
The ECC output stage has an electronic unit which receives the digital control signals and converts them to voltage. If there is no control signal or the fan is disabled, the ECC output stage sends a diagnostic signal to inform the ECC control module of the fault.
If fan speed control lever is set to AUT (automatic) mode, fan speed is influenced by the position of driver's side temperature control dial, driver's side passenger compartment temperature sensor, vehicle speed and engine coolant temperature.
The highest fan speed is selected if driver's side temperature control dial is set to maximum or minimum cooling or heating. The greater the difference between the desired and actual temperatures, as sensed by the driver's side temperature sensor, the higher the fan speed.
As vehicle speed increases, the fan speed will be reduced to maintain a constant airflow throughout the passenger compartment. When heating the passenger compartment after starting a cold engine, the fan speed is gradually increased as engine coolant temperature rises.
RECIRCULATED AIR MODE
The ECC control module selects recirculated air mode only for a combination of cooling and high outside temperature, provided that
- There is a considerable difference between the desired and actual temperature on driver's side. The quantity of recirculated air will vary between 70-100 percent, depending on difference in temperature.
- A high fan speed is manually selected. In this case, the recirculation damper will be set to a mid-position (50 percent of the air will be recirculated).
Recirculation Motor
This motor operates the recirculation damper by means of a mechanical linkage in response to signals from ECC control module.
Recirculation Switch
The off position of recirculation switch corresponds to automatic operation. The ECC control module determines whether recirculation is required.
Air Distribution Switch
With air distribution switch in defroster position, recirculated air mode always cuts out, because humidity in passenger compartment is normally higher than that of outside air.
Recirculation Damper
In AUT (automatic) mode, recirculation damper movement is limited to fractions of a second. It takes about half a minute from full recirculation to take effect, if outside temperature is high.
TEMPERATURE CONTROL
Individual temperature control is provided driver and passenger by means of one damper motor and one cam wheel controlling 2 linkages. ECC control module computes temperature control damper motor position based on inputs from temperature dial settings, passenger compartment temperature sensor, solar sensor, engine coolant temperature sensor and outside (ambient) temperature sensor.
The difference between the desired and actual interior temperature, as monitored by passenger compartment temperature sensor, has a direct effect on temperature control damper positions.
In direct sunlight, the temperature control dampers are positioned to provide a lower temperature, as determined by solar sensor input. If the engine is cold and outside temperature is low, the temperature control dampers are set for more heat to reach the desired temperature faster.
PROGRAMMING ECC CONTROL MODULE
- ECC control module can be programmed with driver position, engine type, passenger compartment ventilation filter, passenger compartment temperature and blower fan speed.
- To program ECC control module, ignition must be on and scan tool connected to Data Link Connector (DLC). Using scan tool, read off DRIVER POSITION, ENGINE TYPE, CABIN FILTER, CABINTEMP and BLOWER FAN SPEED as necessary.
- For DRIVER POSITION, programmable data is LEFT-HAND DRIVE or RIGHT-HAND DRIVE. For ENGINE TYPE, programmable data is GASOLINE or DIESEL. For CABIN FILTER, programmable data is WITH or WITHOUT passenger compartment ventilation filter.
- For passenger compartment temperature, programmable temperature is 3.6°F (2°C) in .9°F (.5°C) steps. For blower fan speed, programmable fan speed is ±17.8 ft 3 /min (8 l/s) in 8.9 ft 3 /min (4 l/s) steps. If ECC control module is programmed for lower airflow, noise level and air circulation will be slightly reduced. If ECC control module is programmed for higher airflow, noise level and air circulation will increase.
SYSTEM TESTS
| 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 SYSTEM SAFETY article in GENERAL SERVICING. |
A/C SYSTEM PERFORMANCE
- Ensure compressor drive belt is okay, fan motor runs at all speeds, and that temperature vents shut completely with temperature switch in full cooling position.
- Ensure that all air comes from panel vents with mode control on vent position, recirculation motor is working, and condenser fan and cooling fan are working.
- Start and warm engine to normal operating temperature. Ensure compressor clutch engages when A/C is turned on. Set temperature switch to full cold position, place mode control to vent position, turn on recirculate air switch and blower fan switch high speed.
- Close engine hood, doors and windows. Run engine at 1500-1600 RPM. Place thermometer in one of the center panel vents. Allow system to stabilize for at least 8 minutes. Check temperature in center panel vent. See «SPECIFICATIONS»(ref-139466-S37623522772002052400000) table.
| Ambient Temp. - °F (°C) | Outlet Air Temp. - °F (°C) |
|---|---|
| 68 (20) | 43-48 (6-9) |
| 86 (30) | 43-48 (6-9) |
| 104 (40) | 43-48 (6-9) |
| (1) Based on a relative humidity of 40-60 percent. | |
| (1) | Based on a relative humidity of 40-60 percent. |
A/C SYSTEM PERFORMANCE SPECIFICATIONS (1)
A/C RELAY CHECK
Remove A/C relay. (Scheme 8) Connect battery positive lead to relay terminal No. 1 (Red wire) and negative lead to relay terminal No. 2 (Blue/Black wire). Continuity should be present between relay terminals No. 3 (Green/Yellow wire) and No. 5 (Gray wire). If continuity is not present, replace relay.
Scheme 8
PIN VOLTAGE TESTS
Note. Perform all voltage tests using Digital Volt-Ohmmeter (DVOM) with a minimum 10-megohm input impedance.
Pin voltage chart is supplied to reduce diagnostic time. Checking pin voltage at ECC control module determines whether it is receiving or transmitting proper voltage signals. See ECC CONTROL MODULE PIN ASSIGNMENTS CONNECTOR "A" and ECC CONTROL MODULE PIN ASSIGNMENTS CONNECTOR "C" tables. Tests may also help determine if control unit wiring harness has short or open circuit.
| Pin No. (1) | Function/Description | Value |
|---|---|---|
| 3 | Signal To A/C From ECM | 10 Volts (On); 0 Volts (Off) |
| 5 | Power Unit Activation | Battery Voltage |
| 7 | Damper Motor Position Sensors | 4.8-5.2 Volts |
| 8 | Left Temperature Damper Control Signal (Motor Activated) | (2) 8-10 Volts |
| 9 | Left Temperature Damper Control Signal (Motor Activated) | (2) 8-10 Volts |
| 10 | Right Temperature Damper Control (Motor Activated) | (2) 8-10 Volts |
| 11 | Right Temperature Damper Control (Motor Activated) | (2) 8-10 Volts |
| 12 | Left Temperature Damper Sensor | 0-5 Volts |
| 13 | Right Temperature Damper Sensor | 0-5 Volts |
| 14 | Power Unit Diagnostic Signal | .22-2.5 Volts |
| 15 | Fan Speed Signal To Power Unit | 100 Hz |
| 16 | Panel Lighting Signal | 125 Hz |
| 19 | Outside Temperature Sensor Signal | About 2.5 Volts At 68°F (20°C) |
| 20 | Engine Block Heater Signal | Battery Voltage (Timer On); 0 Volts (Timer Off) |
| 22 | Signal Ground | 0 Volts |
| 23 | Power Ground | 0 Volts |
| 24 | Damper Motor Air Distribution Control Signal (Motor Activated) | (2) 8-10 Volts |
| 25 | Damper Motor Air Distribution Control Signal (Motor Activated) | (2) 8-10 Volts |
| 26 | Damper Motor Air Recirculation Control Signal (Motor Activated) | (2) 8-10 Volts |
| 27 | Damper Motor Air Recirculation Control Signal (Motor Activated) | (2) 8-10 Volts |
| 28 | Damper Motor Position Sensor Air Distribution Signal | 0-5 Volts |
| 29 | Damper Motor Position Sensor Recirculation | 0-5 Volts |
| 30 | Diagnostic Lead | 8-12 Volts |
| (1) Pin assignments not listed are not used. (2) With motor inactive, less than one volt. | ||
| (1) | Pin assignments not listed are not used. |
| (2) | With motor inactive, less than one volt. |
ECC CONTROL MODULE PIN ASSIGNMENTS CONNECTOR "A"
| Pin No. (1) | Function/Description | Voltage Value |
|---|---|---|
| 1 | Vehicle Speed Signal | Pulsed Signal With Fixed Duty Cycle & Variable Frequency |
| 2 | Engine Coolant Temperature (ECT) Signal From ECM | Pulsed Signal With Fixed Duty Cycle & Variable Frequency |
| 3 | Generator Signal | 12 Volts When Charging; 0 Volts When Not Charging |
| 5 | Power Supply From Ignition Switch | 12 Volts |
| 6 | Pass. Comp. Temperature Sensor Signal | 2.5 Volts At 68°F (20°C) |
| 8 | Pass. Comp. Sensor Fan Motor Signal | 10-12 Volts On; 0 Volts Off |
| 9 | Solar Sensor Signal | Signal Increases With Sun Intensity |
| 10 | Ground Sensor Signal | 0 Volts |
| (1) Pin assignments not listed are not used. | ||
| (1) | Pin assignments not listed are not used. |
ECC CONTROL MODULE PIN ASSIGNMENTS CONNECTOR "C"
SOLAR SENSOR
- Connect scan tool to Data Link Connector located in center console. Turn ignition on. Go into scrolling values. Read off solar sensor signal. Cover solar sensor and read off value, then shine a strong light on sensor and read off value again. (Scheme 7) If values change on scan tool, solar sensor is okay. If values do not change on scan tool, go to next step.
- Check ECC control module and solar sensor connector terminals for poor terminal contact. Repair as necessary. If terminal contact is okay, check for open circuit in Brown/White wire between ECC control module connector terminal C10 and solar sensor. Also check for short circuit to ground or voltage in Gray wire between ECC control module connector terminal C9 and solar sensor connector terminal No. 2. Repair wiring as necessary. If wiring is okay, replace solar sensor.
PASSENGER COMPARTMENT TEMPERATURE SENSOR
Note. Observe how temperature sensor is positioned before attempting removal.