This is the second of three case studies presenting a complete A/C system using aftermarket and OEM (Original Equipment Manufacturers) information. The key to this particular case study is the appreciation of the amount of interpretation which exists with information pre- sented by Autodata. All diagrams supplied by this company are clearly referenced enabling the reader to distinguish between aftermarket and OEM. The diagrams provide some excel- lent examples of how information can be alternatively presented to assist the technician invisualising where system components are fitted.The wiring schematics are very easy to follow and adhere to most of the European requirements with respect to current flow and coding. Information from Autodata is available in a range of formats.This includes technical helplines, books and CD-ROMs. The information from Autodata used within this case study has been accessed from an Autodata A/C CD-ROM.
The case study is not written in textbook fashion. This is because the purpose of each case study is for the reader to appreciate the breadth and depth of information available and what information is required to enable the technician to successfully work on such systems. The author has attempted to try to present the information in a logical order. Explanations have been written to assist in the understanding of system operation. If the reader fails to under- stand a particular aspect of the case study then refer to a section which covers that topic.
Described using after market information courtesy of:
SAAB 900 ACC system (automatic climate control)
Automatic temperature control
Automatic air distribution
Single evaporator – single zone
Expansion valve
Air distribution
The vehicle has a pollen filter that requires replacement at 18 000 miles or 12 months,whichever
occurs first, then every 12 000 miles or 12 months, whichever occurs first.
Figure 3.144
A/C system information
The main purpose of the ACC control module is to control the air-conditioning system so that a comfortable cabin temperature is achieved as soon as possible after starting and then maintained throughout the journey. The ACC control module consists of a display panel with pushbuttons (S292) and an integral control module (A63).The ACC system communicates with other mod- ules to obtain information on other sensor inputs related to A/C operation. Communication is via a data bus link or PWM signal.
ACC (A63) inputs and outputs:
1. ACC unit consisting of panel with integral control module (A63 and S292).
2. Stepper motor for air distribution (M112).
3. Stepper motor air blend damper (M114).
4. Cabin temperature sensor (B37).
5. Solar sensor (B102).
6. DC permanent magnet stepper motor for recirculation damper (M59).
7. Blended-air temperature sensor (footwell vent B160).
8. Fan control unit (feedback and control signal).
9. Engine coolant and heater regulator valve (Y36).
10. Instrument illumination rheostat (R4).
ECM (Engine Control Module) (A35) inputs and outputs:
1. Compressor clutch (Y11).
2. Vehicle speed sensor.
3. Evaporator temperature switch (S51).
4. Triple pressure switch (S341).
SID (SAAB Information Display).A digital multifunction display (A161) with multiplex facility:
1. Outside temperature (B61).
ICE (Integrated Central Electronics).A combination control module (A94):
1. Engine coolant temperature.
2. Condenser fan stages.
A/C amplifier (A175):
1. Heater blower motor.
System layout and components
Figure 3.145
Figure 3.146
Cabin temperature sensor
The cabin temperature sensor is mounted in the dashboard below the ACC control module. It has an integral suction fan which sucks the cabin air past an NTC resistor. Cabin temperature is the ACC control module’s most important parameter. It is compared with the selected cabin temperature to determine whether the temperature of the blended air should be raised or lowered. Cabin temperature is corrected so that it corresponds to the physical perception of the selected temperature, regardless of the outside temperature.When the difference between selected temperature and corrected cabin temperature increases, the speed of the ventilation fan will also increase.When the ignition is switched off the suction fan will continue to run for about 4 minutes. This reduces the risk of incorrect temperature settings if the car is restarted within a fairly short time.
figure...............
Evaporator switch
An anti-frost thermostat on the evaporator prevents freezing and ice building on the evaporator. There is a sensor lying against the evaporator low pressure pipe.When the temperature drops below 2°C the voltage to the compressor is broken.When the temperature exceeds 5°C the thermostat closes again and the compressor is engaged.
Outside temperature sensor
The outside temperature is obtained from the SID via a data bus connection.The sensor is fit- ted under the front bumper.The value of the outside temperature is used by the ACC control module to correct the value of the cabin temperature and to control the speed of the fan.The cabin temperature is corrected so that it corresponds to the physical perception of the selected temperature. This means that the measured cabin temperature is higher than the low outside temperatures. This is true even at high outdoor temperatures, but the difference is less. The condition is dependent on whether heat is passing out of the cabin or into it.At outside tem- peratures below 5°C and over 20°C the fan speed increases to achieve a more consistent cabin temperature.
Sunlight sensor
The solar sensor is placed on top of the dashboard. It measures mainly infrared radiation (heatradiation). In the event of an increase in solar radiation and an outside temperature exceed- ing 15°C the ACC control module increases the ventilation fan speed since more cold air must be supplied.The fan speed is immediately changed in the event of a change in the solar radiation. The fact that the solar sensor measures mainly heat radiation means that it cannot be tested with fluorescent light, only sunlight or light from a bulb must be used.
Rheostat
Display panel lighting value is obtained from the SID.This value regulates the lighting inten- sity of the ACC panel’s display. The same value also regulates the mileometer display in the main instrument display panel and the SID’s own display. In darkness the value is determined by the rheostat and in daylight by the brightness of the light in the cabin so that good read- ability is always obtained.
Pressure switches (trinary switch)
Three switches are built into the receiver drier assembly: a low pressure, high pressure and con- denser fan switch.The receiver drier is positioned on the high pressure side of the A/C system.
figure........
Engine coolant temperature sensor
The temperature of the engine is monitored by the ICE module. This signal is monitored to ensure that if the temperature of the cooling system exceeds 126°C then the A/C compres- sor will not be energised due to the absence of a signal from the ICE module to the ECM module.The coolant temperature is also communicated to the instrument panel.The informa- tion is communicated via a PWM signal with a fixed frequency of 122Hz which varies induty cycle ratio (Figs 3.147 and 3.148).The variation in duty ratio from 10% to 90% corresponds with the coolant temperature.
Figure 3.147
Figure 3.148
Fan speed
The fan is powered directly with a 54V supply from fuse 12.On the ground side the fan is con- nected to a fan control which receives a control voltage of 0–5V from the ACC control module. The fan control also receives a special voltage supply from the ACC control module. The ACC control module receives feedback from the ground side of the fan motor,which gives it informa- tion on the actual voltage across the fan motor. The feedback voltage increases in relation to ground as fan speed decreases. Fan speed is affected in the auto mode of operation as follows:
- As the difference between selected temperature and cabin temperature increases, fan speed also increases.
- Outside temperature below 5°C or exceeding 20°C gives an increase in fan speed.
- An increase in the intensity of the sun at outside temperatures exceeding 15°C gives an increase in fan speed.
The desired fan speed can also be selected manually on the ACC panel. It can be set in ten steps of about 2A each. If the button is depressed for more than one second, fan speed will increase or decrease automatically. Fan speed is shown on the ACC panel display.
Recirculation damper
The recirculation damper is controlled by a DC permanent magnet stepper motor.The damper has only two positions.When the motor has turned the damper to one of the end positions, the current through the motor winding is limited by two PTC resistors, built into the motor.
Air blend motor
The blend door is operated by a hybrid stepper motor. The stepper motor has two windings.A voltage is applied to the windings in special order with short pulses.This causes the motor to move in short steps, hence its name. The direction of rotation can be changed.When the motor is sta- tionary, current is applied continuously to both windings.A stepper motor requires no feedback to the ACC control module. By sending a definite number of pulses, the ACC control module always knows how much the damper moves.A condition for this is that the control module cali- brates itself by rotating the damper to an end position so that the exact position of the damper is known.The air blending damper is set by the ACC control module with the aid of the blended air temperature sensor so that a suitable air temperature will be obtained. The cabin temperature, selected temperature and outside temperature are decisive for the blended air temperature. If the air blending damper is set at the position for maximum cold and this is still insufficient to main- tain the selected temperature, recirculation will be selected. If the selected temperature is ‘HI’ or ‘LO’ the air blending damper will be set to the maximum heat or maximum cold position.
Air distribution
The air distribution stepper motor operates with the same principle as the air blend motor.The air distribution motor varies its rotation to direct air to the following distribution vents:
figure.............
If the requisite blended air temperature is high, air distribution will be set to the defrost/floor position. If the requisite blended air temperature is low, air distribution will be set closer to the defrost position. In the case of requisite blended air temperatures that are extremely low, air distribution will be set to the panel position.As will be realised, air distribution is a function of the requisite blended air temperature.The desired air distribution can also be selected manu- ally on the ACC panel.
System operation – compressor engagement (Fig. 3.152)
A 54 voltage is fed via fuse 3 to the ventilation fan switch. If the switch is in one of the pos- itions 1 to 4 and the A/C button is ON, the voltage is fed to the ICE (Integrated Central
Electronics) module. The ICE module monitors the engine temperature. If the engine temperature is below 126°C a signal is sent to the evaporator temperature switch. If the tem- perature in the evaporator is approximately 5°C or higher, the voltage is fed to the engine management system. The engine management system increases the idling speed and grounds the cable to the three stage pressure switch. If the pressure in the A/C system is higher than 2 bar but lower than 30 bar, the pressure switch grounds the cable to the A/C relay. From fuse 5 (15A), current is fed via the A/C relay to the thermal fuse in the compressor overheating pro- tection. If the temperature in the compressor is lower than 140°C, the current is fed to the solenoid clutch in the compressor.
The engine management system breaks the circuit to the A/C relay in the event of a power- ful acceleration which is received from the throttle position sensor. The evaporator tempera- ture sensor determines if the A/C compressor is running based on the evaporator’s surface temperature.
Auto mode
Select the auto mode of operation.All functions will be controlled automatically.AUTO and the selected temperature appear in the display. Press the Auto button again and all automatically selected settings will be displayed.The electrically heated rear window function can be disabled or activated without leaving the auto mode of operation.
Temperature up or down
Selection of inside temperature is in steps of 1°C between 15°C and 27°C, alternatively steps of 2°F between 58°F and 82°F. If a temperature above 27°C ( 82°F) is selected, ‘HIGH’ is displayed as the selected temperature. Correspondingly ‘LOW’ is displayed if the temperature selected is below 15°C ( 58°F).When both buttons are pressed at the same time for more than 2 seconds the temperature display changes between Celsius and Fahrenheit.
If the selected temperature is ‘HIGH’ in Auto mode, the system sets itself as follows:
figure.................
AUTO is extinguished and fan speed and air distribution are shown.
If the selected temperature is ‘LOW’ in Auto mode, the system will be set as follows:
figure................
AUTO is extinguished and fan speed, air distribution and recirculation are displayed.
Defrost
figure.............
Automatic temperature control still in effect, recirculation cannot be selected. Symbols for the button and activated functions are shown on the display.
Defrost/floor
The air is distributed to defrost as well as the floor and rear side windows, door angle 207°. The button symbols are shown on the display.
Panel
The air is distributed to the panel as well as the rear centre vent, door angle 90°. The button symbol is shown on the display.
Panel/floor
The air is distributed to the panel and rear centre vent as well as to floor and rear side win- dows, door angle 150°. The button symbols are shown on the display.
Floor
The air is distributed to the floor and rear side windows, door angle 180°.The button symbol is shown on the display.
Recirculation
Select recirculation or fresh air. If recirculation is selected the button symbol will be shown on the display.
ECON
A/C and recirculation are turned off. In other respects control takes place as in the AUTO mode. ECON is shown on the display.
Electrical information
Autodata provide information on fuse box and relay layout.This is useful when checking and testing fuses and relays.
Figure 3.149
Figure 3.150
Wire colour coding key (DIN standard)
The table below provides information on the wiring colour used on this vehicle.
figure............
Harness plug identification
Harness plug identification is very important when trying to identify wiring.Technicians often back probe using adaptors to sample live data from such connectors. Pins should be checked to ensure that no corrosion exists and the pins are straight.
Figure 3.151
Circuit diagram key (DIN standard)
The circuit diagram key helps identify the components within the wiring schematic.
figure............
Explanation on wiring diagram (Figure 3.152)
An ignition switch voltage is fed via fuse 3 to the ventilation fan switch pin 37 which is built into the A/C control panel A63/S292. If the blower switch is in one of the positions 1 to 4 and the A/C button is ON, then battery voltage is fed to the ICE module A94 via pin 38 of the A/C mod- ule. ICE module checks the engine coolant temperature across pins 5 and 58 and if the volt drop corresponds to a temperature which is lower than 126°C then battery voltage is sent to the evaporator temperature switch. If the temperature in the evaporator is above 5°C, the voltage is fed to the engine management system A35. The engine management system increases the idling speed and grounds the cable to the three stage pressure switch. If the pressure in the A/C system is higher than 2 bar but lower than 30 bar, the pressure switch grounds the cable to the A/C relay. From fuse 5 (15A), current is fed via the A/C relay to the thermal fuse in the com- pressor overheating protection. If the temperature in the compressor is lower than 140°C, the current is fed to the solenoid clutch in the compressor and the system engages.
The engine management system breaks the circuit to the A/C relay in the event of a power- ful acceleration which is received via a voltage output from the throttle position sensor. The evaporator temperature sensor determines if the A/C compressor is running based on the evap- orator’s surface temperature.The trinary switch will also break the voltage supply to the ECM in the event of a loss of refrigerant or a blockage causing high pressure in the system.
Figure 3.152
Diagnostic information
The table below provides details of the pin and wire configuration from the module to other components within the A/C system. If a pin is not included in the table then it is not used on the module.The test conditions are the operations which are required to obtain the reading.
figure.............
Self-test
Calibration must be carried out if the battery has been disconnected or discharged, or if the ACC panel has been replaced.To start calibration, press the ‘AUTO’ and ‘OFF’ buttons simul- taneously.This also starts a self-test.Calibration and the self-test are carried out in parallel and take less than 30 seconds.All stored faults are cleared at the start and while calibration and self-testing are in progress the number of faults found will be shown on the ACC panel’s dis-play. Calibration must also be carried out if any of the stepper motors have been replaced. Calibration can also be carried out by means of a serial tester.
Erasing trouble codes
Suitable diagnostic equipment is required to erase data from A/C control module fault memory.
figure........ Table 3.10
System repairs
Access to evaporator housing from vehicle interior, removal of fascia panel required.
Access to A/C/heater blower motor from engine bay, removal of fascia panel not required.
Refrigerant charging
Ensure refrigerant circuit is evacuated for a minimum of 30 minutes prior to charging.No fur- ther instructions specified. Refer to refrigerant charging equipment operating instructions.
Refrigerant pressures
To measure the A/C system pressure the following conditions must exist.
Preparatory conditions:
1. All windows and doors closed.
2. All ventilation outlets fully open.
3. Engine idling.
4. Select ‘LO’ on the A/C control module.
5. A/C/heater blower motor set to maximum speed.
6. Recirculation mode selected on the A/C control module.
7. A/C control module set to vent.
8. Run air-conditioning for 5 minutes prior to testing.
Checking:
1. Run engine at 1500–2000 rpm.
figure.......
Delivery temperature
To measure the A/C system delivery temperature from the air vents the following conditions must exist.
Preparatory conditions:
1. All windows and doors closed.
2. All ventilation outlets fully open.
3. Engine idling.
4. Select ‘LO’ on the AC control module.
5. A/C/heater blower motor set to maximum speed.
6. Recirculation mode selected on the A/C control module.
7. A/C control module set to vent.
Checking:
1. Run engine at 1500–2000 rpm.
2. Position temperature probe 100mm into fascia ventilation centre outlet.
3. Measure temperature after 5 minutes.
figure............
Technical data (by kind permission of Autodata Ltd)
figure.............
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