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Air conditioning - Regulation
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CONTENTSThe fault finding procedure 4
Heating circuit 9Additional heating 17Air conditioning 31Questionnaire 50
3
THE FAULT FINDINGPROCEDURE
The importance of the fault finding procedure 5Sequence of events for a fault finding procedure using CLIP 7
The six basic rules 8
4
The fault finding procedure
The importance of the fault finding procedureWhen the systems were relatively basic, the repeated occurrence of certain faultsallowed us to gain experience. This experience often made the cause of a faulteasier to find.
Today, the technical development of vehicles and the increasing complexity of theirsystems require different diagnostic procedures.
When performing fault finding, the fault finding procedure consists of applying alogical and comprehensive procedure of analysis of all the information gatheredon the faulty system.
From a financial point of view, a procedure that is not comprehensive could resultin expensive or even unnecessary operations. Indeed, replacing or even testingsome coded parts allocates them permanently to the programmed system.
Each time a fault finding procedure has to be performed, it is essential to identifythe faulty system correctly and to investigate it thoroughly. This ensures that thecorrect documentation is referred to and that the cause of the fault is found.
The information needed to establish a fault finding procedure is as follows:
• ask the right questions to obtain an exact description of the customer complaint,
• if necessary, run checks and operation tests,
• identify the faulty system correctly,
• carry out the documentary search correctly.
If all of this information is precise, the cause of the fault can be identified morequickly.
5
The fault finding procedure
A fault on a vehicle may appear in one of three ways:
• the faults are recorded by the computers,
• the physical symptoms are detected by the user and checked by the repairtechnician but do not cause a fault to be recorded,
• the physical symptoms are detected by the user but not observed by the repairtechnician during the fault finding request.
The fault finding log
The fault finding log is an essential element for communication with the manu-facturer. It is mandatory to complete a fault finding log each time a fault findingprocedure is carried out on a complex system.
The fault finding log is always requested in the following instances:
• approval request when replacing a part with mandatory approval,
• requests for technical assistance from the Techline (technical department insome countries).
IMPORTANT
This fault finding log is also attached to monitored parts for which returnhas been requested.
6
The fault finding procedure
The fault finding log comes from either NT 3700A, or the Workshop Repair Manualor the CLIP tool (figure 1). The fault finding log should be photocopied or printedout and filled out by hand by the repair agent as they progress through the faultfinding procedure.
Figure 1. The fault finding log may come from CLIP
Sequence of events for a fault finding procedureusing CLIP• Access to known solutions (consult the solutions in the Technical Notes and
information database),
• electronic integrity test (multiplex network),
• automatic fault finding on an electronically detected fault,
• conformity check,
• operational check of the components not tested electronically (search by cus-tomer complaint),
• technical assistance request (create a Customer Complaint Sheet).
NOTEACTIS solutions: operation reserved for authorised personnel.
7
The fault finding procedure
The six basic rules
REMINDERThis table refers to the six essential basic rules for applying a fault find-ing procedure.
1. Gather the information...a) Ask the target questions.
What? What fault has been noticed? Is it actually a fault?
Who? Who has noticed the fault? Who is involved? Who is the user?
Where? Locate the environment or the place in which the fault appears.
When? When did the fault appear? (may be asked before asking "How?") Is it constant?...intermittent? ...cyclical?
How? In what circumstances did the fault appear? Is it on particular occasions?
How often? What is the frequency of the fault? ...its tendency? ...its degree of severity?
b) Use the fault finding support material.(Technical documentation, ACTIS solutions, predefined tools, diagnostic tool, etc.).
2. Carry out an analysisAscertain the faulty function by carrying out a comprehensive analysis of the system by meansof checks (visual, audible, etc.) and, if necessary, tests. Determine whether or not the faultis isolated.Note: Depending on the case, apply the fault finding procedure using the diagnostic tool.
3. Identify the origin of the faultExamine the function as a whole, to obtain possible solutions through reasoning.
4. Eliminate the causeWork on the direct cause. Work according to the prescribed procedure.
5. Correct the faultWork on the faulty system according to the prescribed procedure.
6. Confirm the repair
• Confirm that the customer complaint is no longer present.
• Confirm that the function meets its specifications again by carrying out a conformity checkon the faulty system.
8
HEATING CIRCUITIntroduction to the hot loop. 10
The hot loop within the engine compartment 10The hot loop in the passenger compartment 12
Fault finding on the coolant circuit 14Maintenance of the hot loop 15
9
Heating circuit
Introduction to the hot loop.The combustion in the engine supplies the calorific energy used for the thermalcomfort of the passengers.
The hot loop within the engine compartmentThe hot loop in the engine compartment (figure 2) regulates and maintains thetemperature of the engine.
Figure 2. The hot loop in the engine compartment.
The cooling radiator
The cooling radiator (figure 3) gives off the heat released by the engine, to keepthe latter at a constant temperature.
Figure 3. The radiator.
10
Heating circuit
The cooling fan assembly.
The cooling fan assembly accelerates the thermal exchange between the air fromthe radiator grille and the radiator.
When the vehicle is fitted with a fan, the ventilation speed is modulated by anassembly of two relays.
When the vehicle is fitted with two fans, the fan speed is adjusted by a set of threerelays (figure 4).
Figure 4. The three relays adjust the fan speed.
The thermostat
The thermostat (figure 5) regulates the circulation of the coolant according to theengine temperature.
Figure 5. The thermostat.
11
Heating circuit
Thanks to the thermostat, the rise in temperature of the engine is faster, whichenables the heater matrix to heat up more quickly.
The hot loop in the passenger compartmentThe hot loop on the passenger compartment side (figure 6) heats, mixes and dis-tributes the air.
Figure 6. The hot loop on the passenger compartment side.
The control panel
The control panel (figure 7) allows the user to activate and adjust the different airconditioning functions.
Figure 7. The control panel.
12
Heating circuit
If regulation is in manual mode, the functions are switched on and adjusted by theuser.If regulation is in automatic mode, the functions are switched on and adjusted bythe system.
The heater unit
The heater unit (figure 8) includes the components for the distribution, mixing andrecirculation of air.The heater unit also includes the passenger compartment fan, the evaporator andthe heater matrix.
Figure 8. The components of the heater unit.
1. Evaporator
2. Heater matrix
3. Distribution flaps
4. Proportioning flaps
5. Recirculation flap
The evaporatorThe evaporator allows the blown air to be cooled by the passage through it of therefrigerant fluid.
The heater matrixThe heater matrix assists heat exchange between the outside air and the engineto heat the air in the passenger compartment.
13
Heating circuit
The mixing componentsThe mixing flaps mix the air from the hot and cold loops to achieve the level ofcomfort requested.Depending on the temperature requested, the air is partially or fully directed to-wards the heater matrix, using the mixing flaps.
Certain vehicles have two mixing flaps for separate right/left regulation.
The distribution componentsThe distribution flaps allow the flow of air to be directed to the different areas ofthe passenger compartment.Depending on the request, the distribution flaps direct the air in the vehicle’s ven-tilation circuit.
The air recirculation componentsThe recirculation flap allows the user to choose the source of the air entering thepassenger compartment.Recirculation is the continual cooling or heating of the passenger compartment airto obtain the thermal comfort required quickly.
Fault finding on the coolant circuitA malfunction normally reveals itself in the form of traces of coolant, emission ofsmoke or by means of visual indicators on the dashboard.
A trace of coolant may appear in the following places:
• on the ground,
• in the engine compartment,
• in the passenger compartment.
An emission of smoke may appear in the following places:
• from the exhaust pipe in the form of white smoke (engine hot),
• in the engine compartment,
• in the passenger compartment.
The dashboard warning indicators are the temperature warning light and thecoolant temperature needle.
14
Heating circuit
A malfunction may reveal itself in other forms: a bubbling noise under the dash-board, the level and colour of the coolant in the expansion tank, heavy condensa-tion on the inside of the windscreen.
The thermostatA thermostat malfunction may be revealed in the following forms:
• the engine temperature climbs slowly and the radiator is warm,
• the engine heats up but the radiator remains cold.
Maintenance of the hot loopCertain components of the hot loop in the engine compartment are checked visu-ally or electrically.Certain components of the hot loop within the passenger compartment arechecked visually or electrically.
The hot loop cannot be diagnosed using the diagnostic tool
Cooling circuitThe preliminary checks of the cooling circuit are as follows:
• note the level and check the colour of the coolant,
• check the condition and tension of the water pump drive belt,
• check that the fan, radiator and radiator grille are not obstructed,
• check that there is no trace of leakage in the engine compartment or passengercompartment.
Checking the thermostatTo confirm correct operation of the thermostat, there should be a significant changein temperature between the heater matrix inlet hose and the radiator inlet hose asthe engine warms up. When the engine is warm, the matrix inlet hose and theradiator inlet hose should be at the same temperature.When removed, the thermostat is checked visually.
15
Heating circuit
IMPORTANT
Follow the safety instructions when working on the cooling circuit.
The circuits are under pressure, and it is vital to be aware of the high tem-peratures (risk of serious burns).
Never remove the expansion bottle plug when the engine is hot.
When working under the bonnet, be aware of the possible sudden opera-tion of the cooling fan(s).
Test options
Using the diagnostic tool:
• conformity
Using a multimeter:
• resistance,
• continuity and insulation,
• feeds.
IMPORTANT
On certain vehicles, when removing the thermostat, it is essential to notethe position of the degassing hole.
On thermostats not fitted with the hole, degassing is provided by amoulded bypass within the unit.
Never flush out an engine when it is hot as this could create a thermalshock which could damage certain components.
Consult the technical documentation before carrying out bleeding, flush-ing, refilling or bleeding of the cooling circuit.
After connecting the battery, it is necessary to perform the required pro-gramming operations.
16
ADDITIONAL HEATINGIntroduction to additional heating 18
The thermoplunger heating system 18The auxiliary combustion heating system 20
The passenger compartment heating resistors 23Fault finding on the additional heating systems 25
Maintenance of additional heating systems 27
17
Additional heating
Introduction to additional heatingAdditional heating is designed to reduce the time it takes to attain the temperaturerequested inside the vehicle.
The thermoplunger heating systemThe operating principle of the system
The thermoplunger heating system (figure 9) operates on the cooling circuit toaccelerate the rise in temperature of the coolant.
Figure 9. The thermoplungers.
18
Additional heating
Activation of the system
Activation of the thermoplunger heating system (figure 10) depends mainly on thetemperature of the coolant and of the outside air.
Figure 10. Activation of the heating system.
After activation, the thermoplungers heat the coolant (figure 11).
Figure 11. Heating of the coolant.
19
Additional heating
The auxiliary combustion heating systemAn auxiliary combustion heating system (figure 12) generates greater heatingpower than a thermoplunger heating system.
Figure 12. An auxiliary combustion heating system.
The operating principle of the system
The auxiliary combustion heating system (figure 13) is based on the principle ofcombustion within a heater.
Figure 13. The auxiliary combustion heating system.
20
Additional heating
Activation of the system
Authorisation for activation (figure 14) is managed by the control unit, the temper-ature sensors (air and coolant) and the outside air temperature bimetallic contact.
The combustion request depends on the engine running, the outside temperatureand the temperature of the coolant.
Figure 14. Activation of the auxiliary combustion heating system.
Operation of the system
Once activation has been authorised, the system operates in the following stages:
• start-up,
• regulation,
• switch-off.
21
Additional heating
Start-up of the heating operationUsing the information received and its own internal mapping, the control unit cal-culates the quantities of air and fuel to supply to the heater. Using this calculation,the control unit initiates start-up of the heater (figure 15).
Figure 15. Start-up of auxiliary combustion heating.
Regulation of the heatingHeating regulation is based on a two-phase cycle: full speed and low speed (figure16).
The control device manages the heater speed according to the information re-ceived from the coolant temperature sensor and the overheating switch.
Figure 16. Regulation of auxiliary combustion heating.
22
Additional heating
Switching the heating offThe heater is switched off when the temperature reaches its limit threshold, whenthe engine stops or when a fault is detected.17
Figure 17. Switch-off of auxiliary combustion heating.
The passenger compartment heating resistorsThe operating principle of the passenger compartment heating resis-tors
The passenger compartment heating resistor system (figure 18) heats the passen-ger compartment air directly.
Figure 18. The passenger compartment heating resistors.
23
Additional heating
Activation of the system
The electric heating is triggered when the engine starts (figure 19), and the tem-perature of the heater matrix is not sufficient to heat the air in the passenger com-partment.
Figure 19. Activation of the passenger compartment heating resistor system.
Operation of the system
Air passes into the passenger compartment heating resistor, absorbs the heat pro-duced by the resistors and emerges warm into the passenger compartment (fig-ure 20).
If the starting conditions are met, the air conditioning computer or UCH then con-trols the two relays in three stages.
Figure 20. Activation of the passenger compartment heating resistor system.
24
Additional heating
Switch-off of the system
The passenger compartment heating resistors cease to operate when the enginetemperature reaches a certain level or when one of the starting conditions is nolonger met (figure 21).
Figure 21. Switch-off of the passenger compartment heating resistor system.
Fault finding on the additional heating systemsFault finding on the thermoplungersMalfunction of the thermoplungers is indicated by a lack of heating. If one or moreof the thermoplungers are defective, achievement of the required temperature leveltakes longer.
The injection computer operates the thermoplunger relays.The thermoplungers are operated by relays according to the battery voltage, theair temperature and the coolant temperature.
The coolant circuit should be checked before assuming a thermoplunger fault.
Fault finding on the passenger compartment heating resistorsMalfunction of the passenger compartment heating resistors is indicated by a lackof heating during the first ten minutes of operation.
Depending on the vehicle, the air conditioning computer or the UCH operates theheating resistor relays.
25
Additional heating
Fault finding on the self-contained heaterMalfunction of the self-contained heater is indicated by a lack of heating or noheating at all.
The coolant circuit should be checked before assuming a heater fault.Check the airflow and air distribution. With the engine warm, and with the unit inthe maximum heat position, the blown air should be warm.
Operation of the self-contained heater, independent of user command, is managedby the heater control unit.The heater can be started or stopped using a command mode in the diagnostictool.
Operating safety is provided by a sensor within the self-contained heater (protec-tion against overheating).
IMPORTANT
Certain vehicles may be fitted with a heater programming unit which isavailable as an accessory (see the “TRAFFIC II - Leisure activities” driver’shandbook, “Heating when stationary” section).
Maintenance of additional heating systemsTesting differs according to the additional heating system.
IMPORTANT
Follow the safety instructions whenworking on the additional heating sys-tem.
Disconnect the battery, starting with the negative terminal.
Wait until the heating elements have cooled down (risk of burns).
Before removing the dashboard or seats, always lock the airbag computerusing the diagnostic tool.
26
Additional heating
Checking the thermoplungersThe thermoplungers are supplied with 12 V by two or three relays. One relaycontrols two thermoplungers, and the other relays each control one thermoplunger.
The power of each thermoplunger is about 300 watts, therefore 1200 watts for allfour.The current consumed by each thermoplunger is about 25 amperes, therefore 100amperes for all four.The resistance of a thermoplunger is about 0.5 Ω.
The thermoplungers do not operate in the following cases:– during preheating,– during post heating,– when the heated windscreen is activated,– if the engine speed is less than 600 rpm.
Checks possible: resistance, power supply and conformity of relay operationusing the diagnostic tool.
Checking the passenger compartment heating resistorsThe passenger compartment heating resistors are supplied with 12 volts by relays.The resistance of the passenger compartment heating resistors is about 0.3 Ω.The power of a resistor is about 400 watts on the Renault ESPACE IV.The power of the passenger compartment heating resistors varies according tothe vehicle model, year of manufacture and engine.The current consumed by a resistor is about 35 amperes on the Renault ES-PACE IV, therefore 175 amperes for five resistors.
Configuration of the “Type of heating resistors” (for example: None, 1600 watts or2000 watts for the Renault ESPACE IV) is verified in the computer by reading theconfiguration. Depending on the registration year of the vehicle, the configurationof the heating resistor type may differ (refer to the technical documentation for thechoice of configuration).
The number of resistors is different depending on the vehicle. For example, on theRenault ESPACE IV, if the number of relays is 5, the computer will be configuredto 2000 watts and if the number of relays is 4, the computer will be configured to1600 watts.
27
Additional heating
Verify correct operation of the system by carrying out a current consumption testusing the ammeter.
The conditions necessary for activation of the passenger compartment heatingresistors are as follows:– vehicle engine running,– battery voltage greater than the reference value in the technical documentation,– heating/ventilation blower in operation (at least at the lowest speed),– exterior temperature lower than the reference value in the technical documenta-tion,– alternator "Alternator charge information" authorisation less than the referencevalue in the technical documentation,– injection authorised,– coolant temperature less than the reference value in the technical documenta-tion,– "hot" position selected on the control panel.
Checks possible: current, resistance, power supply and conformity of relay op-eration using the diagnostic tool.
Checking the self-contained heaterThe differences between the diesel and petrol heaters is the layout of the combus-tion chamber and the computer programming.
After engine start-up, if the coolant temperature is less than 75°C and the outsideair temperature is less than 5°C, the heater is switched on. The heater then op-erates at full power until a temperature of 80°C is reached. At between 80°C and85°C, the heater operates at half power. Above 85°C, the heater is switched offand only restarts if the temperature falls below 75°C.
The maximum heating power applied to the coolant is 3300 watts.The maximum fuel consumption of a heater is about 0.4 litre/hour.The maximum electrical power consumption is about 23 watts.After start-up and in operation, the current consumption of the heater is about 2amperes.
The outside air temperature bimetallic contact is a temperature switch located onthe outside of the heater.
The fuel metering pump incorporates a filter which must be changed periodically.
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Additional heating
The resistance of the metering pump is about 10 ohms.The pressure of the metering pump is about 230 millibars.To measure the quantity of fuel, the self-contained heater must be operated. Thesupply of fuel begins about 40 seconds after the self-contained heater is switchedon. Collect the fuel in a graduated measuring cylinder. The fuel supply is inter-rupted automatically after 90 seconds.
The command mode in the diagnostic tool allows operation of the heater to beverified.If the heater does not start, check the following statuses:– the level of fuel in the tank,– the condition of the fuses,– obstruction of the combustion and exhaust air ducts.
The supply voltage of the turbine electric motor is 8 volts.The supply voltage of the glow plug is 8 volts, its current consumption is about 8.5amperes and its resistance is about 0.9 ohms.The heater enters defect mode in the following cases:- if combustion has not started after two start-up attempts,- if the temperature read by the coolant temperature sensor differs from that readby the overheating switch by more than 15°C,- the coolant temperature reaches 125°C,- if the flame detector does not detect any combustion after the second start-upattempt,- if the battery voltage is greater than 16 volts or less than 10 volts.
Note: defect mode is deactivated when the ignition is switched off. The self-con-tained heater will not make another start-up attempt until the vehicle ignition isswitched on again. The fault is stored and can be consulted using the diagnostictool.
The setting of the level of CO discharged at the exhaust of the heater is set in thefactory and cannot be changed in After-Sales.
Checks possible: continuity and insulation, resistance, power supply and confor-mity of operation using the diagnostic tool.
IMPORTANT
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Additional heating
After connecting the battery, it is necessary to perform programming op-erations on some of the vehicle systems.
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AIR CONDITIONINGIntroduction to air conditioning 32
The components of the automatic regulation system 32Switching on the air conditioning 39
Operation of the air conditioning system 40Automatic regulation of the air conditioning 42Switching off air conditioning and safety 44
Maintenance of the air conditioning system 45
31
Air conditioning
Introduction to air conditioningIn automatic mode, only the following parameters are affected by the system:
The components of the automatic regulation systemThe automatic regulation system (figure 22) consists of the following components:
• the sensors,
• the computers,
• the actuators.
The sensors send signals to the air conditioning computer.The air conditioning computer also receives information from other computers.The air conditioning computer controls the actuators to attain the level of comfortrequested.
Figure 22. The components of the air regulation system.
32
Air conditioning
The role of the sensors in the automatic regulation system
The sensors participating in the automatic regulation system are as follows:
• the toxicity sensor,
• the solar radiation sensor,
• the moisture sensor,
• the pressure sensor,
• the evaporator sensor.
Other sensors also take part in the automatic regulation operation, such as theoutside air temperature sensor and the coolant temperature sensor.
The toxicity sensorThe toxicity sensor (figure 23) continuously analyses changes in the concentrationof NOx and CO and sends the results to the air conditioning computer.
Figure 23. The toxicity sensor.
1. The sensitive element of the sensor.
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Air conditioning
The solar radiation sensorThe solar radiation sensor (figure 24) notifies the computer of the intensity of solarradiation, in order to adjust the flow of air to the air vents.
Figure 24. The solar radiation sensor.
The humidity sensorThe humidity sensor (figure 25) measures the variation in humidity in the air in thepassenger compartment.
Figure 25. The humidity sensor.
The humidity sensor consists of the following components:
1. a humidity sensor for the passenger compartment,
2. an internal temperature sensor,
3. a microturbine blowing air over the two sensors.
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Air conditioning
The pressure sensorThe air conditioning computer uses the information from the pressure sensor (fig-ure 26) to decide whether to turn on the air conditioning or not.
Figure 26. The pressure sensor.
The evaporator sensorThe evaporator sensor (figure 27) notifies the computer of the air temperature toprevent freezing of the evaporator.
Figure 27. The evaporator sensor.
35
Air conditioning
The role of the computer in the automatic regulation system
The air conditioning computerThe air conditioning computer (figure 28) receives the signals from the sensorsand other computers, analyses them according to its mapping, and controls theactuators.
Figure 28. The air conditioning computer.
The role of the actuators in the automatic regulation system
The mixing flapsThe mixing flaps (figure 29) mix the warm and cool air.Certain vehicles have two mixing flaps for separate right/left regulation.
Figure 29. The mixing flaps.
36
Air conditioning
The electromagnetic couplingOnce the injection computer has authorised start-up of the compressor, the injec-tion computer or the UCH operates the electromagnetic coupling (figure 30).
Figure 30. The electromagnetic coupling.
The compressor output electrical control valveBy controlling the position of the control valve (figure 31), the computer adjusts thecapacity to adjust the refrigerating power to meet the user’s request for cold air.
Figure 31. The cylinder capacity electrical control valve.
37
Air conditioning
The power modulesThe power modules (figure 32) are of the electronic or resistance type.
Figure 32. The power modules.
Depending on the vehicle type, the passenger compartment blower is supplied byone or two power modules.
The control panelThe control panel (figure 33) sends the user’s instructions to the air conditioningcomputer.
Figure 33. The control panel.
38
Air conditioning
Switching on the air conditioningSwitching on the air conditioning system in automatic mode
In automatic mode, the air conditioning system is switched on by the injection andair conditioning computers and by the Protection and Switching Unit (UPC), de-pending on the vehicle (figure 34).
Figure 34. Switching on the air conditioning system in automatic mode.
The air conditioning computer analyses the temperature inside the vehicle and thetemperature requested in order to switch on the air conditioning system if neces-sary.
The air conditioning computer requests authorisation from the injection computerto switch on the air conditioning.
The engine cooling fan assembly is engaged at the same time as the compressorcoupling.
39
Air conditioning
Starting the air conditioning system in manual mode
In manual mode, pressing the "AC" button sends a direct request to the UCH orinjection computer by cable (figure 35).
Figure 35. Switching on the air conditioning system in manual mode.
Operation of the air conditioning systemWith automatic air conditioning, the temperature stabilises at a value dependingon the exterior temperature.
Automatic mode system operation
In automatic mode, the air conditioning computer analyses the information andfrom it deduces a blown air temperature requirement (figure 36).
Figure 36. Operation of the air conditioning system in automatic mode.
40
Air conditioning
Depending on the blown air temperature chosen, the air conditioning computeroperates the electric control valve to adjust the compressor flow. However, cer-tain compressors are fitted with a pneumatic control valve which opens or closesaccording to the pressure in the low-pressure circuit.
The system can regulate cold production more precisely when it is fitted with avariable capacity compressor.
The computer controls the air mixing motors according to the initial position of theflaps and the blown air temperature instruction.
Depending on the vehicle type, the passenger compartment fan is supplied by oneor two power modules.The power modules are electronic or resistance type.
The air conditioning computer controls themotors that operate the distribution flapsas a function of the internal temperature.
System operation in manual mode
In manual mode, the user directly adjusts the temperature and mix of blown air,until the desired level of comfort is attained.37
Figure 37. Operation of the air conditioning system in manual mode.
41
Air conditioning
Automatic regulation of the air conditioningOperation of air regulation in automatic mode
When the temperature requested is below the outside air temperature, the systemcan activate the air conditioning.38
Figure 38. Operation of air regulation in automatic mode.
The computer adjusts the air conditioning according to the outside temperature,solar radiation, humidity level and the vehicle speed.
The role of the air conditioning computerThe air conditioning computer receives signals from various external sensors:
The air conditioning computer performs several functions:
• It regulates the production of cold air.Cold production and air mixing dependmainly on solar radiation and the outsidetemperature.
• It regulates the ventilation speed.The air ventilation speed dependsmainly on the vehicle speed and the intensityand direction of the sun’s rays.
• It regulates the distribution of the air.The air conditioning computer regulates the distribution of the air.The air distribution depends principally on the humidity level and the intensityof the sun’s rays.
42
Air conditioning
External conditions also affect the control of the recirculation flap.
The recirculation flap and additional heating systems contribute to blown air heatprocessing performance.
On some vehicles, if there is a high risk of misting, the air conditioning computercan engage the "See clear" function
The heat insulating windscreen is used to reduce the influence of solar radiationin the passenger compartment in order to lower the temperature in the vehicleinterior.
Operation of air regulation in manual mode
In manual mode, the switches of the control panel are the main sensors of themanual regulation system (figure 39).
Figure 39. The switches of the manual control panel.
43
Air conditioning
Switching off air conditioning and safetyIn automatic mode, the air conditioning switches off when the operating conditionsare no longer fulfilled (figure 40).
Figure 40. Switching off air conditioning and safety.
In automatic or manual mode, the injection computer can switch the air condition-ing off to prevent the engine from overheating.
The additional heating systems are switched off when the operating conditions areno longer fulfilled.
Maintenance of the air conditioning systemThe air conditioning system can be checked by carrying out an efficiency checkand electrical check using the diagnostic tool or the multimeter.
Sensor check
The air conditioning sensors can be checked using the diagnostic tool and themultimeter.
44
Air conditioning
The conformity check concerns the following specific sensors:
• the toxicity sensor,
• the solar radiation sensor,
• the humidity sensor,
• the pressure sensor,
• the evaporator sensor.
Other more general sensors which take part in the automatic regulation procedurecan be checked using the diagnostic tool.
The toxicity sensorThe toxicity sensor continuously analyses changes in the concentration of NOxand CO in the outside air. The toxicity sensor sends this information to the airconditioning computer which manages the operation of the recirculation flap.The toxicity sensor conformity check is performed using two parameters: CO inlettoxicity and NO inlet toxicity. These parameters, which represent the variationin the levels of carbon dioxide (CO) and nitrogen oxide (NOx) at the air mixing unitinlet, can be displayed using the diagnostic tool.
The sensitive element of the toxicity sensor consists of a layer of metallic oxide.The semiconducting layer is heated by a filament to cause a surface absorptionreaction with the volatile components contained in the ambient air. This absorptioncauses a variation in resistivity which is practically proportional to the concentra-tion of the substances absorbed. The sensitive element of the toxicity sensor isprotected by a membrane. This membrane allows the entry of gas molecules butprevents the entry of moisture and dust.
45
Air conditioning
The sensor has four connections:
• a positive feed,
• a negative feed,
• an NOx toxicity sensor signal,
• a CO toxicity sensor signal.
Each signal is sent separately by a modulated current pulsed at 39 Hertz.
The concentration of NOx and CO in the air is expressed in parts per million (ppm).The value of the parameter corresponding to the concentration of CO varies be-tween 0 and 510 ppm but is also measured as a percentage varying between 0and 100%. The value of the parameter corresponding to the concentration of NOxvaries between 0 and 1 ppm.When the concentration of CO reaches its maximum value (510 ppm) and doesnot fall, the ignition must be turned off several times until this value falls. Underthese conditions, the filament in the sensor neutralises the CO products.
The passenger compartment humidity and temperature sensorsThe unit consists of the following components:– a relative humidity sensor,– a passenger compartment temperature sensor,– a micromotor and a turbine.
The humidity sensor measures the variation in humidity of the air in the passengercompartment.The humidity sensor is of the capacitance type and delivers a signal at a frequencyof between 5.8 kHz and 7.3 kHz, which is proportional to the humidity level.
The passenger compartment temperature sensor is of the Negative TemperatureCoefficient type.
The micromotor is powered at APC and drives a turbine which blows air over therelative humidity sensor and the passenger compartment temperature sensor.
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Air conditioning
The solar radiation sensorThe radiation sensor measures the brightness of the sun in order to adjust the flowof air to the air vents. Its resistance is proportional to the solar radiation.
The radiation sensor is of the photoresistive type.
When performing electrical checks, if the radiation sensor detects a source of light,it is possible to vary the radiation parameter by masking the sensor.The supply voltage of the sensor is 5 volts. The value of the corresponding pa-rameter is expressed in watts on the diagnostic tool.
The evaporator sensorThe evaporator sensor notifies the computer of the air temperature to preventfreezing of the evaporator.
The sensor is of the Negative Temperature Coefficient type. The value of the cor-responding parameter is expressed in °C on the diagnostic tool.The vehicle may be configured asWITH or WITHOUT the evaporator sensor usingthe diagnostic tool.
The pressure sensorThe air conditioning computer uses the information from the pressure sensor todecide whether to turn on the air conditioning or not.
The pressure sensor is of the capacitance type. The value of the correspondingparameter is expressed in bar on the diagnostic tool.
The pressure sensor may be replaced without bleeding the cooling circuit.
Test options
Using the diagnostic tool:
• conformity
Using a multimeter:
• resistance,
• continuity and insulation,
• feeds.
Checking the computers
The computers controlling the operation of the air conditioning system can bechecked using the diagnostic tool and the multimeter.
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Air conditioning
The conformity check involves the computer managing the air conditioning system.The electrical check of the air conditioning computers is carried out using the "con-tinuity test" function, which at the same time measures the resistance and checksfor the presence of interference resistance.
Test options
Using the diagnostic tool:
• conformity
Using a multimeter:
• resistance,
• continuity and insulation,
• feeds.
Checking the actuators
The checks possible on the actuators are those made using the diagnostic tool,the electrical checks and the visual checks (operating the mixing flaps, etc.).
The conformity check involves the following actuators:
• the mixing components,
• the distribution components,
• the recirculation components,
• the electromagnetic coupling,
• the compressor output electrical control valve,
• the power modules,
• the switches on the control panel.
The mixing componentsThe mixing flaps mix the warm and cool air. Certain vehicles have two mixing flapsfor separate right/left regulation.
The distribution componentsCalculations of the risk of misting control the start-up or switching off of the auto-matic demisting system.
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Air conditioning
The risk of misting is calculated using the following parameters:
• the exterior temperature,
• the level of humidity in the passenger compartment,
• the level of solar radiation.
Depending on the risk of misting, the computer may switch on the air conditioningsystem, adjust the cooling performance of the evaporator, increase the air flow atthe demisting outlets, restrict the use of automatic recirculation and automaticallyinitiate electrical demisting of the windows.
The recirculation componentsThe strategy for controlling the recirculation components is applied using two de-tection methods:- detection of rapid changes in pollution (cars, motorcycles, buses, lorries),- detection of an average level of high pollution (driving in an urban area).
The cylinder output electrical control valveThe cylinder output electrical control valve cannot be checked visually.
The control panelThe control panel can be checked visually by pressing the various buttons.
Test options
Using the diagnostic tool:
• conformity
Visually:
• status of the mixing flaps,
• operations on the mixing flaps.
Using a multimeter:
• resistance,
• continuity and insulation,
• feeds.
49
QUESTIONNAIRE
QUESTIONNAIRE1. Which components prevent outside air from entering the passenger compart-
ment?
A The air mixing motor and flap.
B The recirculation motor and flap.
C The distribution motor and flap.
D The proportioning motor and flap.
2. What does the “AC” indicator mean when it is lit on an automatically regulatedair-conditioning system?
A Fault in the cold loop.
B Air conditioning compressor is running.
C Fault in the air conditioning compressor.
D Request for air conditioning.
3. Which components allow mixing of air from the cold loop and air from the hotloop?
A The ventilation motor and flap.
B The distribution motor and flap.
C The proportioning motor and flap.
D The recirculation motor and flap.
4. Which component speeds up heating of the air in the passenger compartmentwhen the engine is cold?
A The evaporator.
B The thermostat.
C The passenger compartment blower.
D The passenger compartment heating resistors.
50
QUESTIONNAIRE
5. What system allows the passenger compartment heating resistors to be acti-vated when the correct driving conditions are not satisfied?
A Automatic demisting.
B Heater control.
C A long press on the “AC” button.
D The diagnostic tool command mode.
6. Which component accelerates warming of the engine?
A The thermostat.
B The cooling fan.
C The water pump.
D The passenger compartment heating resistors.
7. Which component accelerates warming of the coolant?
A The passenger compartment heating resistors.
B The heater.
C The water pump.
D The cooling fan.
8. Which component participates in the conditions for switching on the passengercompartment heating resistors?
A The passenger compartment heating resistor switch on button.
B The solar radiation sensor.
C The alternator.
D The air temperature bimetallic contact.
9. Which computer controls start-up of the thermoplungers?
A UCH
B Injection.
C Air conditioning.
D Protection and Switching Unit.
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QUESTIONNAIRE
10. Which safety instruction must you observe before replacing the thermo-plungers?
A Switch off engine
B Check faults using the diagnostic tool.
C Lock the airbag.
D Disconnect the battery.
11. Which computer authorises activation of the compressor clutch?
A Protection and Switching Unit.
B Injection.
C Air conditioning.
D UCH
12. Which operations must you carry out after replacing the thermostat?
A Flushing, refilling and bleeding.
B Topping up and bleeding.
C Bleeding and topping up.
D Degassing and topping up.
13. Which circuit is affected if the humidity sensor is faulty?
A Mixing.
B Compressor activation.
C Recirculation.
D Compressor regulation.
14. How much current is being consumed by a passenger compartment heatingresistor when the system is supplying 2000 W?
A 30 A.
B 2 A.
C 2000 A.
D 170 A.
52
QUESTIONNAIRE
15. How much heat energy is generated by the heater at maximum output?
A 400 W.
B 3300 W.
C 2000 W.
D 1600 W.
16. What information is sent by the air temperature bimetallic contact to the heater
A Impact detected.
B Outside air temperature threshold.
C Coolant temperature threshold.
D Battery voltage threshold.
17. Which sensor controls the opening and closing of the recirculation flap in aregulated air conditioning system?
A Solar radiation.
B Evaporator temperature.
C Electric control valve.
D Toxicity.
18. Which tool allows a check on the toxicity sensor?
A Gas analyser.
B The opacimeter.
C The multimeter.
D The luxmeter.
19. If the evaporator sensor is not working, what fault could this cause?
A The compressor control valve is always operated at maximum.
B The coolant circuit pressure is increasing.
C No risk.
D The compressor will not be switched off if the evaporator freezes up.
53
QUESTIONNAIRE
20. What does the toxicity sensor measure?
A All toxic gases.
B Pollens and particles.
C Certain toxic gases (CO and NOx).
D Toxic gases, pollens and particles.
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