Automotive Climate Control System (case study 3)

iklan bawah share

This is the last of three case studies presenting a complete A/C system using OEM (Original Equipment Manufacturers) information. 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 understand a particular aspect of the case study then refer to a section which covers that topic. Information from Vauxhall is usually sourced electronically on

Figure 3.153

CD-ROMs.The Vauxhall information system is called TIS 2000 which includes technical infor-

mation, diagnostic routines, bulletins, wiring diagrams, key programming and the facility to

link with diagnostic equipment like TECH 2.

Described using OEM information:

Vauxhall

Electronic Climate Control (ECC)

Automatic temperature control

Single evaporator – dual zone

Expansion valve control

Available for the Vectra-C is a newly developed Electronic Climate Control (ECC) system.

The Vectra-C features a new user interface concept for its ECC system.The system is oper-

ated via a control panel through a menu structure that is displayed on the centrally placed

Graphic Info Display (GID) or Colour Info Display (CID).

Furthermore the system includes features such as:

● air quality sensor;

● dual sun sensor;

● rest-climatisation (reduces hot spots and measures UV intensity);

● remote controlled parking heater (future).

Heating and ventilation

The control panel for the heating and ventilation system incorporates a control module. This

control module controls:

● the position of the flaps;

– air temperature/mix flap (stepper motor);

– air distribution flap (stepper motor);

● the blower speed (four different speeds: supply via shunt resistors or directly by a relay);

● rear window heating.

Without air-conditioning or ECC, the Vectra-C does not feature a recirculation valve.

Figure 3.154

Air filtration

The pollen filter is located under the water deflector and is available as a filter with activated

carbon layer.

Figure 3.155

Control panel heating and ventilation

There is no feedback on the actual position of the mix and distribution flap. Using so-called

overstepping ensures the actual position. If a flap is moved to the fully opened or closed pos-

ition, under certain conditions, the nominal number of steps is increased by 5%, to make sure

the flap reaches this position.Also, when switching OFF the ignition, the flaps are set in the

parking position (fully opened or closed) with 5% overstepping.This means that synchronisa-

tion of the flaps is no longer needed (or even possible).

Controls for electronic climate control

The communication between the A/C control panel and display takes place via the mid-speed

CAN bus.The controls for the ECC feature four switches and three rotary knobs for selection

of the ECC functions.The defrosting, rear screen heating, automatic and recirculating air func-

tions can be activated via the four switches. Each of these functions has a status LED inte-

grated in the switch, which indicates which function is currently active.The temperature is set

separately for the driver and passenger via the left and right rotary knobs. The central knob

serves to manually adjust blower speed and select the ECC functions from the menu. It is dis-

played on the GID (Graphics Interface Display) or CID (Colour Interface Display).The knob

can be turned to the right or left to scroll down the menu, and the menu options are selected

by pressing the centre knob.

Multiplex communication

The ECC is the central control unit for controlling the interior vehicle temperature. For this pur-

pose, it is provided with temperature, air quality and sun sensors in order to measure the current

environmental conditions as well as actuators to actuate the air flaps, the fan and the AC com-

pressor (via the CAN bus system). ECC also actuates the rear screen heating and the auxiliary

heating. In order to prevent overloading the engine (in particular during idling), the ECC

exchanges the ECC operating conditions and request signals with the engine control unit via the

CAN bus. These messages are transmitted to and from the HSCAN and MSCAN via the CIM

(Column Interface Module) (HSCAN to LSCAN) and the GID/CID interface (LSCAN to

MSCAN).

Bus interface to mid-speed CAN (MSCAN)

The ECC has two connections to the mid-speed CAN bus. They serve to loop the mid-speed

CAN bus through the control unit.The control unit electronics are then internally connected

to the looped-through mid-speed CAN bus. If the ECC control unit is not connected, the mid-

speed CAN bus is interrupted.

Display actuation function

Among other tasks, the GID/CID is responsible for the display of all ECC menus. Further-

more, information that needs to be transmitted from the ECC to other control units in the

CAN network is transmitted to the low speed CAN bus by the GID/CID (interface function).

If this information is destined for control units connected to the high speed CAN bus, the CIM

effects the transmission from the low speed CAN bus to the high speed CAN bus.

Dimmed illumination function

The BCM (Body Control Module) transmits the dimming value for the interior illumination

via the low speed CAN bus.After receiving this message, the ECC adjusts the intensity of illu-

mination of the control panel according to the dimming value.

Figure 3.156

Figure 3.157

Figure 3.158

From the main menu it is possible to select:

● air distribution;

● switching the air-conditioning ON/OFF (similar to ECC on the previous systems);

● switching the auto recirculation (by means of the air quality sensor) ON/OFF.

Figure 3.159

When selecting ‘Air Distribution’ and confirming by pressing the centre rotary control, the Air

Distribution menu is displayed.

By selecting the three possible air outlets with the centre rotary control, all possible com-

binations can be made manually.To return to ‘Auto Air Distribution’ select ‘Auto’ from this menu

or press the Auto button on the ECC control panel.

System activation and deactivation

To switch the compressor ON/OFF, select or deselect the option ‘Air-conditioning’. As with 

the Eco button, the heating and ventilation remains in Auto mode but without the help of air-

conditioning.

ECC features an air quality sensor that enables auto recirculation.This feature can be acti-

vated by pressing the recirculation button twice.On Vectra-C auto recirculation is enabled as

default.Auto recirculation can be disabled with the option ‘Air Quality Sensor’ from the ECC

main menu.Recirculation can also be switched ON manually, by using the switch on the ECC

control panel. The manual recirculation has priority over the Auto Recirculation function.

During manual recirculation, the status of the Auto Recirculation remains active.When the

manual recirculation is switched OFF, the Auto Recirculation remains enabled.Again, this is

indicated in the ECC main menu.

ECC components (Figs 3.160 and 3.161)

The ECC system consists of the following components:

● ECC control module/control panel.

● Display (GID or CID).

● Evaporator sensor.

● Output air temperature sensor, outlet footwell left/right and outlet passenger compartment

left/right.

● Dual sun sensor with integrated in-car temperature sensor.

● Air quality sensor.

● Air mix flap stepper motor, left and right.

● Passenger compartment outlet flap stepper motor.

● Footwell outlet flap stepper motor.

Figure 3.160

Figure 3.161

● Defrost outlet flap stepper motor.

● Recirculation flap DC motor.

● Blower with blower control unit.

● Electrical coolant recirculation pump (only when equipped with a parking heater).

● Compressor clutch control coil.

● Parking heater (future option).

● Parking heater remote control (future option).

Pulsation damper

Pulsation dampers are installed to prevent noise, which is generally caused by the pressure

pulses of the compressor.

Figure 3.162

Pressure sensor

To ensure that the air-conditioning system operates safely at all times, the refrigerant circuit is

monitored on the high pressure side.The pressure sensor responds and switches off the compres-

sor if the operating pressure reaches approximately 30 bar.The pressure sensor switches the com-

pressor on again when the pressure drops below the normal operating state of approximately 26

bar.The pressure sensor also switches on the auxiliary fan, depending on outside temperature and

coolant temperature.

Evaporator surface temperature sensor

The ECC system is equipped with a device to prevent icing of the evaporator surface. Instead

of operating as a switch and interrupting the A/C command from the control panel, the Vectra-

C uses a temperature sensor as an input of the ECC control unit.When the evaporator tem-

perature drops below the threshold of 1.5°C, the ECM (Engine Control Module) will

receive a signal from the ECC control module via the CAN bus to deactivate the compressor

clutch.At 1.2°C, the compressor is activated again.

Outlet air temperature sensors

Four NTC resistors (10 k at 25°C) are used to measure the temperature of the air coming out

of the heater housing: two for the floor outlets (left/right) and two for the upper outlets

(left/right).The ECC control unit determines the desired position of the air mix flaps through

the input from these sensors.

B77 dual sun sensor with in-car temperature sensor

The function of the dual sun sensor is to determine the sunlight intensity.The sensor is equipped

with two identical photodiodes for direction recognition.The signals are supplied to the ECC con-

trol module via two separate terminals.The sun sensor is located on the centre of the instrument

panel on the defroster nozzle.The sensor does not only contain the photodiodes but also the in-

car temperature sensor (NTC, 5 k at 25°C) (Fig. 3.163).

Figure 3.163

Figure 3.164

Figure 3.165

Air quality sensor

The air quality sensor (see also Fig. 3.52) is located under the water deflector, left of the pollen

filter (Fig. 3.164).This forms an input signal for the automatic recirculation.Like the pollen fil-

ter and the activated charcoal filter, it helps improve the on-board climate. By chemical reac-

tions on its surface, the air quality sensor is able to detect localised ground level contamination,

such as harmful diesel or petrol fumes.At traffic lights, e.g. when directly behind a truck or if

driving through a tunnel, exhaust gas peaks occur which can be up to 1000 times higher than

the exhaust gas concentration in the general environment.

If the vehicle is in such an exhaust gas cloud, the air intake process will always be stopped

and the system will switch to recirculation mode. To prevent the air quality in the passenger

compartment from becoming worse than the air outside, which could happen in some cases if

recirculation mode were on permanently and the air in the passenger compartment was not

being exchanged at all, the system works dynamically. In exceptional cases such as these, this

mode of operation ensures that an adequate supply of fresh air is fed into the system. For tech-

nical data see section 3.2.

Stepper motors

The ECC system operates five stepper motors, two for the temperature blend function (one

motor for the driver temperature zone and one for passenger temperature zone), and one each

for the following, defrost flap (windscreen), face flap ventilation and floor flap. For motor spec-

ification see Fig. 3.165.

Figure 3.166

Blower motor with voltage regulator

The blower voltage regulator is connected to the ECC control module via a command line and

a diagnostic line. Using a PWM (see section 3.2) signal the ECC control unit reports the

desired blower speed to the blower voltage regulator.The blower control module controls the

blower motor through a 2KHz PWM signal. Figure 3.166 provides a wiring diagram.

ECC special features

The following special features apply to the ECC system.

Rest-climatisation

It is possible to make use of the residual heat/cold of the HVAC system after the ignition is

switched OFF. If the Auto button on the control panel is pressed, after ignition OFF, the ECC

is activated and the display indicates the ambient, driver and passenger temperature and the

rest-climatisation symbol (‘Residual Air-conditioning On’).

It is now possible to adjust the desired temperature.The blower speed is fixed and cannot be

adjusted manually in the rest-climatisation mode.

With an increasing deviation between the desired and actual outlet air temperature, the blower

voltage is gradually reduced to 0V.Below a battery voltage of 10.7V, the rest-climatisation mode

is disabled.

Rest-climatisation and anti-theft warning system

It is possible to activate the rest-climatisation, leave and lock the vehicle.When equipped with

an Anti-Theft Warning System (ATWS), the circulation of air may cause problems when arm-

ing the interior monitoring (ultrasonic module).

To prevent this, the interior monitoring is deactivated/disabled with a request/message from the

ECC control module to the BCM (Body Control Module). Once the rest-climatisation stops, a

message from the ECC control module to the BCM ensures that the interior monitoring is armed.

Blower delay

Similar to previous ECC systems, in the Auto mode the blower speed is gradually increased after

an engine start.This is done to cool down the evaporator first, before a large amount of air flows

through it.The delay depends on the ambient temperature and can extend up to 8 seconds.This

delay can be overruled manually by increasing the blower speed with the centre rotary control.

Figure 3.167

Defroster delay

If the defrost button is pressed after an engine start, the defrost flap remains closed up to a max-

imum of 30 seconds.During this delay, the air is directed to the footwell to get rid of the mois-

ture in the heating and ventilation housing.This way, fogging up of the windows is prevented in

defrost mode. Like the blower delay, the defroster delay depends on the ambient temperature.

Logistic mode

In the Logistic mode, the ECC cannot be disabled completely, because the defrost function for the

windscreen is required by law.All after-run functions (ignition OFF) are disabled because their

only function is comfort and not safety. Furthermore the ECC control module is not allowed to

‘wake up’ any of the CAN buses, or activate the parking heater (future option) or rest-climatisa-

tion.The flaps remain in the last position used.No overstepping is performed after ignition OFF.

Electrical information

Fuse box information illustrated using Vauxhall’s TIS (Technical Information System which is

CD-ROM based).

Fuse box/relay plate

 figure 3.168

tabel

Figure 3.169

tabel

ECC block diagram

The block diagram in Figure 3.170 illustrates the input and output relationships between the

A/C system module,A/C components and other modules that share information via a multiplexed

network. The use of the component information chart is used to match the codes with the 

Figure 3.170

Figure 3.171

components (DIN Standard Codes).Once an understanding of the block diagram is achieved

make use of the wiring schematic.

Component information

ECC system wiring schematic

The wiring schematic and pin layout in Figure 3.171 is used to aid the understanding of the

operation of the system.

Explanation of wiring schematics

The ECC is the central control unit for controlling the interior vehicle temperature.This mod-

ule controls all the heating and ventilation controls and acts as a user interface by including

selection knobs and switches. The module controls HVAC door motor positions and blower

speed based on information provided from sensor inputs on temperature, sun intensity and air

quality.The ECC module also controls the independent heater (see Chapter 1).The ECC has

two connections to the mid-speed CAN bus. They serve to loop the mid-speed CAN bus

through the control unit. The control unit electronics is then internally connected to the

looped-through mid-speed CAN bus. If the ECC control unit is not connected, the mid-speed

CAN bus is interrupted.

In order to prevent overloading the engine (in particular during idling), the ECC exchanges

the ECC operating conditions and requests signals with the engine control unit via the CAN

bus.These messages are transmitted to and from the HSCAN and MSCAN via CIM interface

(HSCAN to LSCAN) and the DIS interface (LSCAN to MSCAN).The activation of the A/C

compressor is not carried out by the ECC module, it is activated upon a request signal gener-

ated by the ECC module which is sent to the engine control module (A84) via the CAN bus

system.

P6 (information display,Graphics Information Display (GID), Colour Information Display

(CID)) shares information on a medium speed CAN data bus. Information will consist of sig-

nals for display purposes (temperature and blower speed etc.). The communication between

the control panel and display takes place via the mid-speed CAN bus.Among other tasks, the

GID/CID is responsible for the display of all ECC menus. Furthermore, information that

needs to be transmitted from the ECC to other control units in the CAN network is transmit-

ted to the low speed CAN bus by the GID/CID (interface function).

Important

If this information is destined for control units connected to the high-speed CAN bus, the CIM

effects the transmission from the low-speed CAN bus to the high-speed CAN bus. For exam-

ple, if the evaporator temperature sensor (B5-A14) output voltage equated to a temperature

approaching ice formation on the evaporator housing then this signal would be sent via the

MSCAN to P6. The signal would then be sent from P6 (display) to BCM (A15 body control

unit) via the LSCAN.The BCM is connected to the CIM (A105 column integrated module) via

the LSCAN. The CIM has the facility to interface with LSCAN and HSCAN systems so the

signal will travel via the HSCAN to the ECM (A84 engine control module). Upon receiving

the signal the ECM will de-energise the compressor coil.

figureeee.....................

Engine Control Module (ECM) – compressor control (Fig. 3.172)

Compressor clutch L7 is controlled by the ECM. The ECM provides a ground signal to K8

compressor relay. This allows current to flow from relay K8 to compressor coil L7 and to

ground. Current will also flow to pin 4 of the ECC module.This acts as confirmation that the

ECM has activated or deactivated the A/C compressor clutch.

The compressor has a control pressure sensor to protect the system in case of overpressure

or loss of pressure.This signal is sent to the ECM enabling the clutch to be de-energised in the

event of a system failure.

Diagnostic information

These are the procedures to be followed to obtain the required test results.

Delivery temperature

Preparatory conditions:

1. All windows and doors closed.

2. All ventilation outlets fully open.

Figure 3.172

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.

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...............

Refrigerant pressures

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...............

Self-diagnosis

The A/C control module fault memory can only be checked using diagnostic equipment con-

nected to the Data Link Connector (DLC).

Trouble codes

Suitable diagnostic equipment is required to obtain and erase data from A/C control module

memory. See Table 3.11 for a list of codes.

Data logger using Tech 2 – ECC system

Table 3.12 provides a data list that was obtained from a vehicle at the Vauxhall Training Centre 

by the author. The data list was accessed using the scan tool Tech 2. Note this data is not 

live but simulated by the module (interfaced) to enable the technician to understand what

operating conditions and input/output information is being received and sent by the ECC

module.

figure,,,,,,Table 3.11

Table 3.12

Actuator tests

The following actuator tests are available using a Tech 2 tester:

● Recirculation motor test results: recirculation – moving – fresh.

● LED test on display results: dim/bright.

Technical data

figure............

Service note

The dashboard does not need to be removed to gain access to the evaporator.

iklan bawah postingan

Automotive A/C Auto Temp Control System (case study 2)

iklan bawah share

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:

1. As the difference between selected temperature and cabin temperature increases, fan speed also increases.
2. Outside temperature below 5°C or exceeding 20°C gives an increase in fan speed.
3. 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.............

iklan bawah postingan

Automotive A/C Manual Control System (case study 1)

iklan bawah share

This is the first of three case studies presenting a complete A/C system using OEM (Original

Equipment Manufacturers) information. 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. Photos of system components have been added to help visualise their pos-

ition and explanations have been written to assist in the understanding of system operation. If

the reader fails to understand a particular aspect of the case study then refer to a section which

covers that topic.




Information from Ford is usually sourced electronically via an intranet. The Ford informa-

tion system includes training and technical information, diagnostic routines, bulletins and wiring

diagrams.




Ford manual control system (Fiesta)

Described using OEM information.




Manual temperature control

Single evaporator

Single zone




System information

The manual control system used by this manufacturer has a manual blower control selection,

manual air distribution, manual temperature control, and switch operated A/C and recircula-

tion.The only information the module must process is based on A/C switch input, recirculation

input, and temperature variation for the solenoid operated water control.The blend door and

air distribution are all Bowden cable operated except for the recirculation door which is DC

motor operated. The electronic circuitry required for the operation of such a system is very

simple.The module has no memory functions (EPROM) cannot be programmed and is not a

part of a multiplex network.This means that the circuitry is designed as an ASIC (Application

Specific Integrated Circuit).The output from the unit can be monitored by more electronically

advanced modules like the Powertrain Control Module (PCM).




Filtering

A pollen filter is fitted as standard. This cleans the incoming fresh air of pollen and dirt par-

ticles. It must be renewed after every 40 000 km under normal operation conditions, or after

20 000 km under difficult conditions.




Air distribution

The blower motor has four speeds, controlled by the blower motor operating switch through

a resistor pack.The position of the air distribution flap is adjusted by a splined shaft.The recir-

culation air flap is operated by a servo motor. If the air-conditioning system is switched on

but the blower motor switched off, the air-conditioning system will not operate. The air-

conditioning system will only operate if the blower motor is on.The temperature control and

air distribution flaps are controlled by two operating cables.Air is supplied to the windscreen

and side windows regardless of the air distribution setting. If the air distribution rotary control

is turned to the ‘Defrost’ or ‘Foot well/Defrost’ position, the air-conditioning is switched on

regardless of the position of the air-conditioning switch or blower switch.As a result, the air in

the vehicle used to defrost the windows is dehumidified before being distributed.




Face level

The main flow of air enters the passenger compartment at face level.




Face level /floor level

The main flow of air enters the passenger compartment in equal parts at face and floor level,

and a small amount flows to the demister nozzles of the side windows.




Floor level

The main flow of air enters the passenger compartment at floor level, and a smaller amount

flows to the demister nozzles of the side windows.




Demist /floor level

The main flow of air enters the passenger compartment in equal parts at the windscreen and

at floor level, and a smaller amount flows to the demister nozzles of the side windows.




Demist

The main flow of air enters the passenger compartment at the windscreen and a smaller amount

flows to the demister nozzles of the side windows.




A/C system

The system uses an FOV valve which is explained in detail in Chapter 1, section 1.8. Later sys-

tems can have a variable orifice valve fitted.




Figure 3.131




A/C system operation

The temperature is set manually through the heater control module.The heater control mod-

ule operates the heater control valve cyclically (up to 18 cycles per minute) according to the

occupants’ temperature selection which is sensed by a potentiometer inside the heater control

module.This controls a heater control solenoid which regulates the flow of coolant to the heat

exchanger.The air-conditioning switch activates the air-conditioning relay through the heater

control module.This relay applies voltage to the low pressure switch.The low pressure switch

controls the operating cycles of the compressor according to the pressure on the low pressure

side of the refrigerant circuit. If the low pressure switch is closed then the PCM will receive a

voltage signal.When the air-conditioning is activated, the compressor clutch and cooling fan

(stage 1) are energised.




The A/C system will be deactivated in the event of the following:

1. Engine overheating sensed by the coolant temperature sensor 120°C.

2. Engine under load, TP sensor output 3.4 volts. So the full engine power is available for

vehicle acceleration.

3. Compressor cycling switch is below lower threshold approximately 1.6 bar.

4. High pressure switch is open, indicating excessive pressure in the system 30 bar.

5. Internal blower fan not operating.

6. Compressor thermal protection device becomes open circuit.




When the air-conditioning is switched off, the compressor clutch is immediately de-energised.

The cooling fan continues working for a further 40 seconds.The maximum cut-off time for the

compressor clutch with a wide open throttle is 12 seconds.When the air-conditioning is switched

on, the cooling fan (stage 1) is switched on at once.Then, after a delay of about 2 seconds, the

compressor clutch is switched on. If the cooling fan is already switched on, this time is reduced

to 1 second. Switching the cooling fan on in advance ensures that the condenser is cooled

before hot refrigerant gas flows through it. For the first stage the voltage of the cooling fan is

restricted by a ballast resistor. This circuit is closed by means of a relay. For the second stage

the full voltage is provided for the cooling fan through a second relay. Both relays are con-

trolled by the PCM.




The cut-in conditions for the relay for the first stage are as follows:

● Coolant temperature exceeding 95°C once and then remaining over 92°C.

● Air-conditioning switched on.

● Relay for the second stage pulled up.




The cut-in conditions for the relay for the second stage are as follows:

● High pressure switch (P1) closed for at least 5 seconds.

● Coolant temperature exceeding 100°C and then remaining over 97°C.

● Coolant temperature over 95°C for more than 15 seconds and engine speed over 4000 rpm at

full load (WOT).




The vehicle battery has two terminals. A positive terminal and a negative (earth/ground)

terminal.All the electrical power required to run electrical systems will come from this source.

The power supply the battery provides would eventually diminish unless it was topped up. The

alternator carries out this task and maintains the battery’s power supply while the engine is run-

ning.There is a network of cables that runs from the battery power supply to various electrical

systems.Most electrical systems are protected by a fuse.These are located in fuse boxes.




Most manufacturers use a Battery Junction Box (BJB fitted as close to the battery as pos-

sible) and Central Junction Box (CJB generally inside the vehicle) to house fuses, relays,

diodes and sometimes diagnostic connectors. The BJB will contain fuses and relays mainly

related to systems under the bonnet (hood) of the vehicle.The CJB will support the rest of the

power supply to all the other systems.




Battery (01) supply has a DIN designation 30 BA610RD (Fig. 3.132).There is a permanent

feed (not switched), charging system designation (BA), large diameter (10mm2

), high current carrying capacity wire unprotected by a fuse going to the generator (alternator). This is the main power supply of the starter motor and the main feed to the battery from the alternator

to keep the power supply above 12V.




Figure 3.132




Figure 3.133




This power supply from the battery also provides power to the BJB bus bar, a bar inside the

BJB which is fitted to all the fuses and acts as a supply line. In Figure 3.131 the FSC codes are

all 30 meaning permanent feed.This means that the fuses will always remain live at this point.

It does not mean that the circuit will be fully operational all the time. Remember the circuit

will only be live when current can flow through it. Often the BJB supplies a feed to the CJB

(Fig. 3.133).This is why there are often high current rated fuses in the BJB because it feeds a

range of other circuits elsewhere in the system.




This also means that if one of these fuses blows (becomes open circuit) a large number of

systems will not operate. Power distribution is like a pyramid system, at the very top is the bat-

tery positive terminal and at the bottom all the circuits that receive their power from a fuse,

control unit/module or the ignition switch.




Manual A/C schematics

Block diagram




Figure 3.134




Components

A128 heater control module

The heater control module has the heating, ventilation and air-conditioning switches built into

the unit (see Figure 3.88). It is this unit which communicates the information on heating tem-

perature, air recirculation and A/C demand to other components. The heater temperature is

set using the temperature control switch built into the heater control module called a poten-

tiometer. The potentiometer operates a heater control solenoid valve (Y100), which controls

the flow of hot coolant through the heat exchanger. Depending on the setting of this switch,

the heater control module monitors the position of Y100 and varies the voltage applied to it to

control the coolant flow through the heat exchanger.




Figure 3.135




A147 powertrain control module

The powertrain control module controls all of the electrical operations of the engine, for

example fuelling, ignition and diagnostics. It is also used to control the A/C.The block diagram

in Figure 3.134 shows that a wire goes from K32 to the engine control module A147. K47 is

used to supply power to the compressor clutch and can only be operated by A147 when pro-

viding an earth path to the relay.




N75 A/C compressor cycling switch (low pressure and cycling switch)

As described earlier in this chapter this switch acts as a safety device to prevent icing of the

evaporator and operation if no refrigerant is present in the system by becoming open circuit

(open so no current can flow).




Air-conditioning system – low pressure switch/cycling switch

The low pressure/cycling switch is fitted on the accumulator housing which is situated between

the evaporator and the compressor.When the air-conditioning is switched on, the clutch only

receives 12V if the low pressure switch is closed.When the pressure falls below 1.6 bar, the low

pressure switch is opened and the supply of current to the compressor clutch is interrupted.

The low pressure switch functions as a de-icing switch and controls the compressor clutch

on/off cycle.The pressures in the low pressure line and evaporator are practically equal.As the

pressure in the low pressure line drops, the temperature in the evaporator approaches freezing

point. There is a risk that the evaporator will ice up and lose its cooling power. The low pres-

sure switch opens the compressor clutch when the pressure drops to a certain level and will not

close it again until the pressure has risen to a suitable level.




N76 dual pressure switch

Switch one is normally open (high speed fan switch). The high pressure switch is fitted in the

high pressure line between the condenser and orifice valve. The function of the high pressure

switch is to protect the high pressure section of the refrigerant circuit.When pressure exceeds

the maximum value of 31.4 bar because, for instance, the air flow through the condenser is

impeded or the high pressure line is blocked, the high pressure switch turns the compressor off.

The compressor will not be switched on again until the pressure has dropped back to 17.2 bar.




Switch two is normally closed (high pressure switch). The fan speed must increase when

the pressure is more than 20.7 bar to enable additional cooling of the condensor. A147, the

powertrain control module (main engine control module), will not switch the fan to a lower

speed until the pressure has dropped back to 17.2 bar.




Figure 3.136




K158 A/C switch relay

Located in the BJB this relay is operated by the heater control module once A/C has been acti-

vated by the occupants.Upon activation a voltage will go to the low pressure switch and then

to the A147 powertrain control module where under the right conditions the module will acti-

vate K32 to send power to the A/C compressor clutch.




K45 engine cooling fan relay

Operated by A147 (providing an earth path to the relay) this allows the fan to operate at a low

speed due to reduced current flow via a resistor R27.




K46 high speed engine cooling fan relay

Operated by A147 (providing an earth path to the relay) this allows the fan to operate at max-

imum speed to a direct power supply.




K32 A/C wide open throttle relay

Operated by A147 and provides power to the compressor clutch Y16.




N125 blower motor switch

A four speed, five position switch which directs current through a resistor pack R21.




R21 heater blower series resistor

A series resistor pack, providing a range of resistances to reduce the current flowing through

the motor M3 enabling speed control.




R27 engine cooling fan resistor

A resistor which enables reduced current flow to the engine cooling fan motor M37.




P91 Central Junction Box (CJB)

Situated inside of the vehicle and contains relays and fuses.The wiring schematics provide all

the information on the fuse and relay requirements.




Figure 3.137

Figure 3.138

Figure 3.139




P93 Battery Junction Box (BJB)

Situated near the battery and contains fuses and relays.




Y100 heater control solenoid valve

A solenoid operated valve controlling the flow of heated coolant (hot water mixed with

antifreeze) to the heat exchanger inside the vehicle.




Figure 3.140

Figure 3.141




Y16 A/C compressor clutch with built-in thermo-time switch

The compressor clutch is an electromagnetic unit with an internal resistance of 3 .A thermo

switch is integrated in the compressor; at a temperature of 115°C in the compressor outlet

(high pressure side), this switch cuts off the power supply to the magnetic clutch in the event

of the unit overheating.




V7 A/C compressor clutch diode

A diode is used to protect the electrical system from any back-emf (electromotive force) or

voltage spikes caused by the clutch being operated.




M69 recirculation air actuator

The recirculation air flap is operated by an electronic stepper motor (see section 3.2). The elec-

tric stepper motor has two cables attached to a lever which when operated opens and closes

the recirculation doors (see Figure 1.29).




M3 blower motor

The blower motor has four speeds, controlled by the blower motor switch (N125) through a series

resistor pack (R21). If the air-conditioning system is switched on but the blower motor switch

is off, the air-conditioning system will not operate unless the rotary control switch is turned to the

‘Defrost’ or ‘Footwell/Defrost’ position, the air-conditioning is switched on regardless of the posi-

tion of the air-conditioning switch or blower switch.As a result, the air in the vehicle used to

defrost the windows is dehumidified before being distributed. In demist/defrost mode the heater

control module provides an earth path to the blower motor switch enabling the blower motor

to operate.




Electrical system

Explanation of manual control system wiring schematic

When vehicle electricians analyse a vehicle wiring schematic they generally follow a set pattern:

1. Power supply signals.

2. Earth/ground signals.

3. Input – sensors.

4. Output – actuators.




When working on a system which incorporates an ECU (Electronic Control Unit,A128,A147)

electricians will often take all electrical readings from the ECU connector. Some systems have

built-in diagnostics and will display a fault via a code; other systems require a diagnostic tester

to be plugged into a standard diagnostic connector on the vehicle to retrieve information

based on the system’s performance. Even when this has been achieved wiring schematics are

still required to be examined.What happens if the diagnostic plug is faulty? Often technicians

are not taught to read wiring schematics and rely too heavily on diagnostic test equipment.

Research and development engineers still set up rigs in test cells and have to wire systems up

manually. Understanding wiring diagrams promotes a greater depth of system operation and

develops excellent diagnostic skills.




Heater control module circuit

Voltage supply

Voltage is always present at the heater control module (A128) pin 2 C41 (connector 41).With

the ignition switched on, the heater control module (A128), the heater control solenoid valve

(Y100), the recirculation air actuator (M69) and the heater blower motor (M3) receive volt-

age. The heater control motor is controlled by switching the earth path hence 31S at pin 5.

When the air-conditioning is switched on using the switch at the heater control module (A128),

the heater control module (A128) provides a ground signal via pin 11 of A128 (earth, 31S) for

the A/C switch relay pin 1 (K158).The A/C will not be switched on unless the blower motor is

on or the air distribution is switched to defrost. Pin 4 of A128 is live when the sidelights are

switched on to illuminate the display. The heating temperature is controlled by the tempera-

ture selector switch (13) at the heater control module (A128).The heater control solenoid valve

(Y100) is timed by the heater control module (A128 – see Figure 3.129 on page 201).




In this way the supply of heating water to the heat exchanger is controlled. Changes from

outside air to recirculated air operation are made using the switch (1) at the heater control

module (A128).The heater control module (A128) then sends a switched ground signal to the

recirculation air actuator (M69) via pin 9 of the module (A128).




Blower motor circuit

The blower motor and recirculation air actuator receive power from F16 once the ignition

switch has been operated to start or run (DIN code 15).The speed of the heater blower moto

(M3) is controlled via the heater blower switch (N14). If the blower motor is off and the air

conditioning is operating in demist conditions then the heater blower motor (M3) receives

ground signal from the heater control module (A128) pin 7 – see Figure 3.127 on page 196.




Testing blower motors

All tests should include power and earth connections/fuses etc. Testing the circuit operation is

best suited to current measurement.This is also the most dangerous.This could be achieved by

removing fuse F16 and placing an ammeter capable of drawing 25–30 amps or using an amp clamp

around the wires.This will give the health of the electric motor and resistors.Alternatively dis-

connect switch N125 and provide an earth path with a fusible link. Be very careful the blower

motor draws a high current which can create heat or damage testers.Often shunts are used to

reduce the possibility of damage and provide the ability to measure high current flow.Testing

using the wrong cable thickness could act as a hot wire! Always look at the cable thickness and

fuse rating if in doubt:M3 pin 2,wire code 31S – CA18 4BK/RD which is a 4mm2

cross-sectional

area of high current carrying capacity.Any switched earth/grounds 31S can often be tested using

an LED or power probe. If the circuit is constantly being switched on and off the LED will

flash green for earth and red for live.




A/C signal to the PCM (Fig. 3.142)

The relay (K158) then closes, thereby sending a signal to pin 10 of the Powertrain Control Module

(PCM) (A147) via the A/C compressor cycling switch (N75). If there is no refrigerant in the sys-

tem (below 1.6 bar) then the switch will be open circuit and the signal will not reach A147, thus no

A/C system operation. The PCM (A147) controls the A/C Wide Open Throttle (WOT) relay

(K32) via pin 47.By providing a ground (earth) to the relay, power can flow from fuse 32 (F32) to

dual pressure switch (N76) and providing system pressure is not excessive the power will go to the

WOT relay (K32). The A/C compressor clutch (Y16) and the A/C compressor are switched on.

The A/C compressor cycling switch (A75) interrupts the voltage supply to pin 41 of the PCM

(A147) when the system pressure decreases. Consequently, the compressor is turned off by the

PCM (A147) via the A/C WOT relay (K32) in order to avoid ice formation in the evaporator.

When the pressure increases, the A/C compressor is turned on again.




High speed condenser fan (Fig. 3.143)

At the same time the second contact of the dual pressure switch (N76) closes and signals the

Powertrain Control Module (PCM) (A147) to run the engine cooling fan motor (M37) at high

speed.The PCM (A147) then sends a signal to the high speed engine cooling fan relay (K46)

which bridges the engine cooling fan resistor (R27).




System diagnostics

Assuming the clutch is not engaging, refrigerant pressure exists and the technician has selected

to carry out some electrical tests.




Initial diagnostics

Initially, treat the A/C system as operating between two control systems, one being the heater

control module and the other the Powertrain Control Module (PCM). The heater control

module sends an A/C demand signal via the low pressure switch to the PCM. This is a good

starting point if the A/C cycling switch is easy to access. The voltage level should be battery

voltage.A connector view is available from the manufacturer if unsure which wire to check. If

the A/C cycling switch is difficult to access then remove the A/C relay K150 and place either a

power probe,LED tester, or multimeter (continuity or current test) on the relay coil pin which

is provided with a ground signal by the heater control module. If using an LED/power probe

the green LED will light up. Switch the A/C on and off to check the operation of the heater

control module.Remember the A/C switch and blower fan must be running for the ground sig-

nal to be sent. If the signal is present then system diagnostics will focus on the PCM receiving

the signal and the A/C coil being operated. If the signal is not present then diagnostics will

work backward to verify why the signal is not being sent.




Figure 3.142




If the signal is being sent, carry out a relay test on K32.Test to see if the PCM is providing a

ground signal to the relay to activate the A/C system. If the ground is not provided then the fault

exists where the PCM does not want the A/C system to run.This is due to the following reasons:




● It has not received the signal from the A/C relay.

● It has received an input from a sensor providing a signal which is out of operational parame-

ters, i.e. engine coolant over 120°C or below 5°C, throttle position sensor over 3.8V.




Figure 3.143




In this event the PCM will not provide a ground signal to the WOT relay.

A/C relays are always a good starting point for initial electrical diagnostics.




WOT relay is not receiving a ground signal

Check that the A/C signal is being received by the PCM.This can be done at the module con-

nector pin 10 C1159.A connector view can be obtained.A break-out box is sometimes useful

and reduces the possibility of any damage to the connector block.A multimeter or oscilloscope

can be used to verify the correct voltage level. First measure the voltage at pin 10 by placing the

meter probe (red) on pin 10 and the ground probe (black) on ground (for zero reference). Then

carry out a power-to-power check.This is done by placing the red probe on the battery positive

terminal and the ground probe on pin 10.This will check the potential difference between the

two signals.A difference no greater than 0.2V should be present. If greater than this amount

then a resistance exists in the system. If no voltage is present is the first instance then an open

circuit exists possibly due to a faulty A/C switch.




If the signal is being received then a full ‘PCM pin’ test is required starting with all PCM

power supplies and ground signal. ‘Power-to-power’ and ‘ground-to-ground’ tests must also be

carried out to check pds across supplies. On successful completion the coolant, throttle and

vehicle speed sensors should be checked.




During these tests you can provide your own feeds and earths using power probes to test the

system’s response. Never trick the A/C system to switch on if you have no evidence that the

system has sufficient refrigerant and oil.Always seek advice when unsure.All tests should be

carried out at the connector pins using the correct connector terminal fittings (connector pin

kits or break-out box kits).




Serial testing

The heater control module is not accessible via serial testing.The PCM will provide DTCs and

data lists but the A/C information will be limited to the cycling switch, throttle position sensor,

vehicle speed sensor and engine coolant temperature sensor. The data list will provide infor-

mation on whether the PCM is functioning correctly and if it is receiving power.




The serial test is certainly a quick and easy test to carry out and is worth conducting before

any detailed electrical diagnostic testing is done.




Erasing trouble codes

The manual control system uses the PCM to operate the A/C clutch.The PCM receives a sig-

nal from the heater control module via the A/C relay and cycling switch. The only relevant

diagnostic trouble codes available are A/C cycling switch signal, engine related vehicle speed

sensor, engine coolant temperature sensor, and throttle position sensor. Diagnostic trouble

codes are removed using a diagnostic scan tool. Carry out a dealer drive cycle upon retrieval

and removal of codes.




Self-diagnostics

No self-diagnostics are available on this model and year.




System control

Three pressure switches are used to control A/C operation. A compressor cycling switch is

used due to an FOV being fitted. A dual pressure switch is used to protect the system from

overpressure and two operate the secondary condenser fan when the system is under load.




figure .......................




Refrigerant pressures

Preparatory conditions:

1. Pollen filter in good condition.

2. Engine idling and above 85°C.

3. A/C running (5 minutes).

4. Blower speed maximum.

5. Recirculation on.

6. A/C temperature to maximum cold selection.

7. All vents open.




figure..................




Delivery temperature

Preparatory conditions:

1. All windows and doors closed.

2. All ventilation outlets fully open.

3. Engine idling.

4. Select cold on the A/C temperature control knob.

5. A/C/heater blower motor set to maximum speed.

6. Recirculation mode selected.

7. Air distribution knob set to face (centre 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............




Description Fill capacity/adjustment

figure.................




Since 07/99 vehicles have a fluorescent tracer dye tablet inserted into the A/C system. If tracer

dye is present, there is a green cross on the suction accumulator.




System repairs

The dash panel must be removed to gain access to the evaporator on this model. iklan bawah postingan