MPaPressure208Service.Self-Study Programme 208Air Conditioner in the Motor VehicleFundamentals1,6 1,4 1,2 1,0 0,8 0,6 0,4 0,2 0 -30 -20Temperature-10o0 C10203040506070air dition conAir conditioning systems have long ceased to be regarded as luxury equipment. Air conditioners have become a factor in active safety, and today can almost be considered as an integral part of a vehicle's safety specification. 10 years ago, only about 10 percent of all newly registered vehicles were fitted with an air conditioning system. By 1996, air conditioners were being installed as standard in more than one in four newly registered vehicles. Customer demand for air conditioning is rising continually.The design of the refrigerant circuit of an air conditioner is identical in all vehicles. Air conditioner refrigerant circuits only vary in respect of how they are adapted to meet refrigeration requirements. In this Self-Study Programme, you will familiarise yourself with the basic purpose and design of an air conditioner. You will learn the functions of the component parts in the refrigeration process, the special characteristics of the refrigerant and why air conditioners require special service specifications. The component parts shown in the following SSP are common to most air conditioners.Please note that the figures specified are given by way of example only. Depending on refrigeration requirements, the absolute values vary from vehicle to vehicle.New Important NoteThe Self-Study Programme is not a Workshop Manual!Please always refer to the relevant Service Literature for all inspection, adjustment and repair instructions. Service literature.2Table of ContentsThe in-car climate . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4Why air conditioning?Applied physicsMPaThe physics of the cooling system . . . . . . . . . . . . . . . . . . . . . . . . 6oCThe refrigerant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 The cooling system . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12The principle of the refrigerant circuit Refrigerant circuit with expansion valve The compressor The mode of operation of the compressor Magnetic clutch The condenser The fluid container and drier Expansion valve Expansion valve – new generation The evaporator Refrigerant circuit with restrictor The restrictor The collecting tank134aRSystem control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32Components of the safety systemCooling fan circuit . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 40Fan circuit for engine/condenser cooling Radiator fan control unit J293t° pTemperature control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 42Manual control Automatic control System overview Control unit with operating and display unit The main temperature sensors Auxiliary signals for temperature control Positioning motor Air ducting Air distribution Air recirculation modeTechnical service . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 64Safety precautions General information on function influencing factors Fault diagnosis through pressure testing Fault diagnosis through self-diagnosisInformation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 72Key cooling system terminology3The in-car climateWhy air conditioning?People feel comfortable at a certain ambient temperature and atmospheric humidity. As a component part of active safety, the driver's well-being is a key factor in driving ability. The “in-car climate“ has a direct bearing on the driver, fatigue-free driving and driving safety. A comfortable interior temperature is dependent upon the prevailing ambient temperature and upon sufficient air flow: Low ambient temperature, e.g. –20 oC Higher interior temperature 28 oC High air flow rate: 8 kg per min.Interior temperature– In strong sunlight in particular, the heated cabin air can only be exchanged for air with ambient temperature. – In addition, the air temperature usually rises en route from the intake point to the air outlet. – Opening a window or sliding roof or setting a higher fan speed for greater comfort will usually result in a draught and expose the occupants to other nuisances such as noise, exhaust gases and pollen.Comfort curves°C kg/minHigh ambient temperature, e.g. 40 oC Low interior temperature 23 oC High air flow rate: 10 kg per min. Moderate ambient temperature, e.g. 10 oC Low interior temperature 21.5 oC Low air flow rate: 4 kg per min. Even modern heating and ventilation systems have difficulty maintaining a pleasant climate inside a vehicle at high ambient temperatures. Why?28826624422220 -20 -10 0 10 20 30 40 °C0Air flow rate208_043Ambient temperatureHigh levels of atmospheric humidity put the body under considerably greater physical strain.Temperatures in a mid-range passenger car where: driving time 1 h ambient temperature 30oC sunlight penetration into car Area Head Chest with air conditioning without air conditioning23 °C 24 °C42 °C 40 °CFeet28 °C35 °C208_0014Effects of an unfavourable vehicle interior temperature on humansComfort rangeScientific studies conducted by the WHO (World Health Organization) have shown that one's ability to concentrate and reactions are impaired when under stress. Heat puts a strain on the body. The best temperature for the driver is between 20 and 22 oC. This is equivalent to climatic load A, the "comfort range". Strong sunlight can increase the interior temperature by more than 15 oC above the ambient temperature– particularly in the head area. This is where the effects of heat are most dangerous. The body temperature rises and the heart rate increases. Heavier perspiration will typically occur, too. The brain is not receiving enough oxygen. Also refer to "climatic load range B". Climatic loads in range C put an excessive strain on the body. Physicians specialising in traffic-related illnesses refer to this condition as “climatic stress“. Studies have shown that an increase in temperature from 25 to 35 oC reduces one's sensory perception and powers of reasoning by 20%. It has been estimated that this figure is equivalent to a blood alcohol concentration of 0.5 millilitres alcohol level.ABTranspirationCStrainHeart rateBody temperature Climatic load moderatelowhigh208_042The air conditioner - a system which keeps the air temperature at a level comfortable to humans, as well as purifying and dehumidifying the air -– was created in order to reduce or eliminate completely such stress. With the help of an air conditioner it is possible to produce at the air outlets a temperature which is much lower than high outside air temperatures. This is possible both when the vehicle is at a standstill and when it is in operation. A technical side-effect of air conditioning is that the air is dehumidified and cleaned at the same time. However, this is just as important as the reduction in temperature. The pollen filter and activated charcoal filter also help to clean the air entering the vehicle. People with allergic illnesses benefit greatly from being able to breathe clean air.- a real safety element In-vehicle air conditioning is - a functional accessory not only for expensive tastes5Physics of the cooling systemApplied physicsMPaLawsoCMany substances are known to exist in three aggregate states. Take water for example: solid – liquid – vapour. The principle of cooling follows this law. Even in ancient times there was a need for cooling. One of the first methods used to cool foodstuffs was to store them in an “icebox“. The ice (water in a solid aggregate state) absorbs the heat of the foodstuffs, thereby cooling them down. The ice melts as a result, assuming another aggregate state, namely that of a liquid (water). If the water is heated further, it will boil and evaporate. The water is now in the gaseous state. The gaseous substance can be converted back to a liquid by cooling it and will become a solid again if cooled further. This principle is applicable to almost all substances: – A substance absorbs heat when it is converted from a liquid to a gas.Ice – solid208_039Ice – becomes a liquid when it absorbs heat208_040Water – becomes a gas when it absorbs heatAES208_041Law– A substance gives off heat when it is converted from a gas to a liquid.– Heat always flows from the warmer substance to the colder substance. Air conditioners utilise the effects of heat exchange, a process in which a substance changes state at certain points.Freezing point, e.g. water becomes ice, Boiling point e.g. water becomes steam6Pressure and boiling point If the pressure is changed using a liquid, the boiling point changes. All liquids behave similarly. Boiling point H2O/water Machine oil = = 100 C 380 - 400 oCoThe evaporation process is also used in vehicle air conditioners. A substance with a low boiling point is used for this purpose. This substance is known as a refrigerant. Boiling point Refrigerant R12 –29.8 oC Refrigerant R134a –26.5 oC (The boiling points specified for liquids in the table always refer to an atmospheric pressure of 0.1 MPa = 1 bar.)Vapour pressure curveR134a R12 40MPaoCThe lower the pressure, the lower the temperature at which water boils (evaporates).Vapour pressure curveH2O 1,7 17 4,01,5153,5351,3 MPa13 MPa bar3,030 bar1,1112,525Liquid0,9 9 2,0Liquid20Pressure0,77Pressure1,5150,551,010Gaseous0,3 3 0,5Gaseous50,1 100 110 120 130 140 150 160 170 180 190 20010 -40 -20 0 20 40 60 °C 80 1000Temperature°CTemperature208_006208_005What does a vapour pressure curve tell us?We can draw the following conclusions from the vapour pressure curve for the two refrigerants R134a and R12 (R12 is no longer used) and water: – At a constant pressure, the vapours become a liquid through temperature reduction (in the air conditioner circuit, this process takes place in the condenser = liquefier), – The refrigerant goes from a liquid state to a vapour state through pressure reduction (in the air conditioner circuit, this process takes place in the evaporator).7The refrigerantThe refrigerant with a low boiling point used for vehicle air conditioners is a gas. As a gas, it is invisible. As a vapour and as a liquid, it is colourless like water. Refrigerant R 1 2 – Dichlordifluormethane chem. formula CCl2F2 a chlorinated hydrocarbon (C F C ) harmful to the environment! Refrigerant R 1 3 4 a – Tetrafluorethane chem. formula CH2F-CF3 a fluorocarbon (F C ) environmentally friendly!134aRRefrigerants may not be combined with each other. Only the refrigerant specified for the system in question may be used.With regard to vehicle air conditioners, the sale and filling of refrigerant R12 were banned in Germany with effect from 1995 and July 1998 respectively. In current automotive air conditioners, only refrigerant R134a is used. – R134a – a fluorocarbon contains no chlorine atoms - unlike refrigerant R12 - which cause depletion of the ozone layer in the earth's atmosphere when they split. – The vapour pressure curves of R134a and R12 are very similar. R134a has the same refrigeration capacity as R12. It is possible to adapt air conditioners which now may no longer be filled with R12 to R134a with a special conversion kit (Retrofit method). The systems converted in this way are no longer able to match their original refrigeration capacity.Ordinance banning halogensR134a16 bar 14 12 10Liquid ExpansionPressure8 6 4 2 0 -30 -20 -10 0 10 20 30 40 50 60 70oEvaporation Gaseous TemperatureDepending on the pressure and temperature conditions in the refrigerant circuit, the refrigerant will either be a gas or a liquid.CVapour pressure curve of R134a208_0508State of refrigerant R134a in the cycle in an air conditioner In addition to the vapour pressure curve, the cycle shows the change of state of the refrigerant under pressure and temperature in addition to the energy balance at which the refrigerant returns to its original state. The diagram is an excerpt from the state diagram of refrigerant R134a for a vehicle air conditioner. Different absolute values are possible in dependence upon the demand of a vehicle type for refrigeration capacity.Temperature curve Saturated liquid4,0The energy content is a key factor in the design of an air conditioner. It shows what energy is required (evaporator heat, condenser heat) to achieve the intended refrigeration capacity. Physical data of R134a: Boiling point: Freezing point: Critical temperature: Critical pressure: –26.5 –101.6 100.6 4.056 (40.56 °C °C °C MPa bar)134aRCritical point (pressure/temperature)Temperature curve Saturated vapour4090MPa2,0 1,67070 60 50 40 30C502060B161,040 30 20 2010 8Pressure0,80,660,4101040,30 C0 CD0,2 200 240 280 320 360 400A44032Energy contentkJ/kg208_053ABCompression in the compressor, pressure and temperature rise, gaseous, high pressure, high temperature Condensation process in the condenser, high pressure, temperature reduction, the liquid leaves the condenser slightly cooled Expansion = sudden pressure relief, results in evaporation Evaporation process (heat absorption) in the evaporator. Transition path from vapour state to gaseous state (low pressure) Temperature curve at point BFor a glossary refer to page 72.BCC DD APressurebar8090 85 809The refrigerantRefrigerants and ozone layer Ozone protects the earth's surface against UV radiation by absorbing a large proportion of these rays. UV rays split ozone (O3) into an oxygen molecule (O2) and in an oxygen atom (O). Oxygen atoms and oxygen molecules from other reactions combine again to form ozone. This process takes place in the ozonosphere, a part of the stratosphere at an altitude of between 20 and 50 km.kmUVUVUVUVUV200 100 80 60134aRSTRATOSPHÄRE40+Cl=O3 20 O2 10Cl ClOOLike R12, chlorine (Cl) is a constituent of a CFC refrigerant . If handled improperly, the R12 molecule will rise up to the ozone layer– since it is lighter than air–. UV radiation liberates a chlorine atom in the CFC, and this atom reacts with the ozone. In the process, the ozone decomposes leaving an oxygen molecule (O2) and chlorine monoxide (ClO), which then reacts again with oxygen and liberates chlorine (Cl). This cycle can repeat itself as many as 100,000 times. However, free oxygen molecules (O2) cannot absorb UV radiation. Refrigerants and global warming The sunlight impinging upon the earth's surface is reflected in the form of infrared radiation. However, trace gases – most importantly CO2 – reflect these waves in the troposphere. This causes the earth's atmosphere to heat up,– a phenomenon which is commonly referred to as "global warming". CFCs are heavily responsible for the increasing trace gas concentration. 1 kg of R12 has the same greenhouse effect as 4000 tons of CO2. R134a only makes a small contribution to global warming. Its ozone depletion potential is nil.TROPOSPHÄRE5FCKWGlobal warmingFCKW1208_051Reaction between CFC and ozone in the atmosphere (CFC = FCKW)Ozone depletion potentialFCKW R12 1FKW R134a 0 0 1 2 3 4Greenhouse potential208_05210Refrigerant oil A special oil – the refrigerant oil – free of impurities such as sulphur, wax and moisture is required to lubricate all the movable parts in the air conditioner. The refrigerant oil must be compatible with the refrigerant itself, because some of the refrigerant oil mixes with the refrigerant in the refrigerant circuit. In addition, the refrigerant oil must not attack the seals used in the system. No other oils may be used, as they lead to copper plating, the build-up of carbon deposits and the formation of residues which can cause premature wear and irreparable damage to movable parts. A special synthetic oil is used for the R134a refrigerant circuit. This oil may only be used for this particular refrigerant, since it does not mix with other refrigerants. Also, the refrigerant oil can only be adapted to a specific compressor type. The refrigerant for R134a Designation: P A G = Polyalkylene glycol Important notes: Properties: - high solubility in combination with refrigerant - good lubrication properties - acid free - highly hygroscopic (water-attracting) - cannot be mixed with other oils N.B.: - must not in be used in older refrigeration systems filled with refrigerant R12, since it is incompatible with R12 – Do not store in the open (highly hygroscopic). – Always keep oil tanks closed to protect them against the ingress of moisture. Close opened drums immediately. – Do not use old refrigerant. – Dispose of as toxic waste. Refrigerant may not be disposed of together with engine oil or gear oil because of its chemical properties.Compressor50%10% 10%Condenser Fluid container Evaporator10% 20%Suction hose134aRDistribution of oil quantity in the refrigerant circuit (roughly) The filling quantity of refrigerant varies according to the design of the units used in a particular type of vehicle.11The cooling systemThe principle of the refrigerant circuitThe cooling process and the technical conditions We know that: Too cool down an object, heat must be given off. A compression refrigeration system is used in motor vehicles for this purpose. A refrigerant circulates in the closed circuit, continually alternating changing from a liquid to a gas and vice versa. The refrigerant is: – compressed in the gaseous state, – condensed through heat dissipation – and evaporated through pressure reduction and heat absorption. Cool air is not produced, heat is extracted from the air flow in the vehicle.Low-pressure sideHigh-pressure sideHow does this process work?Compressor208_071The c o m p r e s s o r induces cold, gaseous refrigerant at a low pressure. The refrigerant is compressed in the compressor, causing it to heat up. The refrigerant is pumped into the circuit on the high-pressure side. In this phase, the refrigerant is in a gaseous state, has a high pressure and a high temperature.Cooling airCondenser12208_073Valve Cooled fresh airThe compressed liquid refrigerant continues to flow up to a narrowing. This narrowing can be in the form of a restrictor or an expansion valve. Once the refrigerant reaches the narrowing, it is injected into the evaporator causing its pressure to drop (low-pressure side). Inside the e v a p o r a t o r, the injected liquid refrigerant expands and evaporates. The evaporation heat required for this purpose is extracted from warm fresh air which cools down when it passes through the evaporator fins. The temperature inside the vehicle is reduced to a pleasant level. In this phase, the refrigerant is in a vapour state, under low pressure and at low temperature.Evaporator Warm fresh air208_004208_072208_074The refrigerant follows the short path to the c o n d e n s e r (liquefier). Heat is now extracted from the compressed, hot gas in the condenser by the air flowing through (headwind and fresh air blower). The refrigerant condenses and becomes a liquid when it reaches its melting point (pressuredependent). In this phase, the refrigerant is therefore in a liquid state, has a high pressure and a medium temperature.Now in the gaseous state again, the refrigerant emerges from the evaporator. The refrigerant is again drawn in by the compressor and passes through the cycle once again. Thus, the circuit is closed.In this phase, the refrigerant is again gaseous, has a low pressure and a low temperature.13The cooling systemRefrigerant circuit with expansion valveI H GWorking pressure HD = High-pressure ND = Low pressure In technical documents such as Workshop Manuals, the components are represented in a diagrammatic form.ND HDND HDABCD EF 208_032I 1HEDA BThe refrigerant circuit is activated when the vehicle engine is running. For this purpose, the compressor has a magnetic clutch. 1 MPa = 10 bar The absolute values are always vehiclespecific. Please observe the Workshop Manual.2C 2Condensation Pressure approx. 1.4 MPa (14 bar) Temperature reduction: 10 oC114Pressures and temperature in the circuit (example) Compression ratio at approx. 1.4 MPa (14 bar) Temperature approx. 65 oCLegend High pressure Low pressureThe components: A B C D E F G H I Compressor with magnetic clutch Condenser Fluid container with drier High-pressure switch High-pressure service connection Expansion valve Evaporator Low-pressure service connection Damper (vehicle-specific)FGThe refrigerant circuit may not be opened for safety reasons. If it is necessary to open the refrigerant circuit in order to perform repair work on the vehicle, the refrigerant must be drawn off beforehand using a suitable service station.3 4208_031The refrigeration capacity of a vehicle air conditioner is dependent upon the car-specific installation conditions and the vehicle category (passenger cars, vans). The components A to H exist in every circuit. Additional connections can be provided for service work, temperature sensors, pressure switches in the high- and low-pressure circuit and oil drain screws depending on the circuit design and requirements. The layout of components within the circuit also differs from one vehicle type to another. Some systems have a damper before the compressor in order to dampen refrigerant vibrations.The pressures and temperatures in the circuit are always dependent on momentary operating state. The specified values are intended as a rough guideline only. They are reached after 20 min. at an ambient temperature of 20 oC and at engine speeds of between 1500 and 2000 rpm. At 20 oC and when the engine is at a standstill, a pressure of 0.47 MPa (4.7 bar) will build up inside the refrigerant circuit. The components of the refrigerant circuit with expansion valve will now be examined more closely (for details of the refrigerant circuit with restrictor refer to page 28).341208_033Evaporation Expansion from approx. 1.4 MPa (14 bar) to approx. 0.12 MPa Pressure: approx. 0.12 MPa (1.2 bar) (1.2 bar), Temperature: from approx. 55 oC to –7 oC Temperature: approx. –7 oC15The cooling systemThe compressorThe compressors used in vehicle air conditioners are oil-lubricated displacement compressors. They operate only when the air conditioner is switched on, and this is controlled by means of a magnetic clutch. The compressor increases the pressure of the refrigerant. The temperature of the refrigerant rises at the same time. Were there to be no pressure increase, it would not be possible for the refrigerant in the air conditioner to expand and therefore cool down subsequently. A special refrigerant oil is used for lubricating the compressor. About half of it remains in the compressor while the other half is circulated with the refrigerant. A pressure shut-off valve, which is usually attached to the compressor, protects the system against excessively high pressures.208_028The compression process The compressor draws in cold, gaseous refrigerant through the evaporator under low pressure . It is "vital" for the compressor that the refrigerant be in a gaseous state, because liquid refrigerant cannot be compressed and would destroy the compressor (in much the same way as a water shock can damage an engine). The compressor compresses the refrigerant and forces it towards the condenser as a hot gas on the high-pressure side of refrigerant circuit.208_045CompressorMagnetic clutchThe compressor therefore represents the interface between the low-pressure and highpressure sides of the refrigerant circuit.16Mode of operation of compressorCompressors for air conditioners operate according to various principles: – – – – Reciprocating compressors Coiled tube compressors Vane-cell compressors Wobbleplate compressorsWobbleplate compressors will now be examined in more detail. The turning motion of the input shaft is converted to an axial motion (= piston stroke) by means of the wobbleplate. Depending on compressor type, between 3 and 10 pistons can be centred around the input shaft. A suction/pressure valve is assigned to each piston. These valves open/close automatically in rhythm with the working stroke. An air conditioner is rated for the max. speed of the compressor. However, the compressor output is dependent on engine rpm. Compressor rpm differences of between 0 and 6000 rpm can occur. This affects evaporator filling as well as the cooling capacity of the air conditioner. Controlled-output compressors with a variable displacement were developed in order to adapt compressor output to different engine speeds, ambient temperatures or driver-selected interior temperatures.208_027Input shaft Wobbleplate Wobbleplate compressor (non-self-regulating) Angle of wobbleplate constant Displacement constantSuction/ pressure valve PistonCompressor output is adapted by adjusting the angle of the wobbleplate. In constant-displacement compressors, compressor output is adapted to the demand for refrigeration by switching the compressor on and off periodically via the magnetic clutch.Piston Wobbleplate208_046Wobbleplate compressor (self-regulating) Angle of wobbleplate variable Displacement variable17The cooling systemThe self-regulating compressor runs continously in air condition mode Control range of compressor All control positions between upper stop (100 %) and the lower stop (approx. 5 %) are adapted to the required delivery rate by altering the chamber pressure. The compressor is on continuous duty during the control cycle!Calibrated restrictor bore Regulating valve Wobbleplate Slide railInput shaft High pressureLow pressureUpper side PistonLower sideSprings Chamber pressure Drive hub208_047The turning motion of the input shaft is transmitted to the drive hub and converted to axial motion of the piston via the wobbleplate. The wobbleplate is located longitudinally in a slide rail. The piston stroke and the delivery rate are defined by the inclination of the wobbleplate. I n c l i n a t i o n – dependent on the chamber pressure and hence the pressure conditions at the base and top of the piston. The inclination is supported by springs located before and after the wobbleplate.C h a m b e r p r e s s u r e – is dependent upon the high and low pressures acting upon the regulating valve and by the calibrated restrictor bore. High pressure, low pressure and chamber pressure are equal when the air conditioner is off. The springs before and after the wobbleplate set it to a delivery rate of about 40%. The advantage of output control is that it eliminates compressor cut-in shock, which often manifests itself in a jolt while driving.18High delivery rate for high cooling capacity - low chamber pressureRegulating valveBellows 2Bellows 1Chamber pressureRestrictor boreChamber pressure208_048Spring 1Spring 2High pressureLow pressureThe high and low pressures are relatively high. – Bellows 2 is compressed by the high pressure . – Bellows 1 is also compressed by the relatively high low pressure. – Regulating valve opens. Chamber pressure is reduced via the low-pressure side.– The combined force resulting from the low pressure acting upon the upper sides of the piston and the force of spring 1 is greater than the combined force resulting from the chamber pressure acting upon the lower sides of the piston and the force of spring 2. Inclination of wobbleplate increases = large stroke with high delivery rate19The cooling systemLow delivery rate and low cooling capacity - high chamber pressureRegulating valveBellows 2Bellows 1Chamber pressureChamber pressureRestrictor boreSpring 1Spring 2208_049High pressureLow pressureThe high and low pressures are relatively low. – Bellows 2 opens out. – Bellows 1 also opens out as a result of the relatively low pressure. – Regulating valve closes. The low-pressure side is closed against the chamber pressure. – Chamber pressure rises via the calibrated restrictor bore.– The combined force resulting from the low pressure acting upon the upper side of the piston and the force of spring is greater than the combined force resulting from the chamber pressure acting upon the lower sides of the piston plus the force of spring 2. Inclination of wobbleplate decreases = small stroke with low delivery rate.20Magnetic clutchThe drivetrain is connected between the compressor and vehicle engine while the engine is running by means of the magnetic clutch. Design The clutch comprises – Belt pulley with bearing – Spring plate with hub – Magnetic coilSchematic diagram of clutch switched offABelt pulley with bearingCompressor Input shaftSpring plate with hubThe hub of the spring plate is permanently mounted the compressor input shaft. The belt pulley is mounted in a pivot bearing on the housing of the compressor at the shaft output. The magnetic coil is permanently connected to the compressor housing. There is an open space “A“ between the spring plate and the belt pulley. Function The vehicle engine drives the belt pulley (Arrow) by means of the ribbed V-belt. The belt pulley follows on freely when the compressor is switched off. When the compressor is connected, voltage is present at the magnetic coil. A magnetic force field is created. This force field draws the spring plate towards the rotating belt pulley (the open space “A“ is bridged) and makes a positive connection between the belt pulley and the input shaft of the compressor. The compressor runs on. The compressor runs on until the electrical circuit to the magnetic coil is opened. The spring plate is then retracted by the belt pulley by means of springs. The belt pulley again runs without driving the compressor shaft.Magnetic coilCompressor housing,208_002Schematic diagram of clutch switched onForce flow208_003For compressor switch-on and switch-off conditions– refer to Air conditioning function control.21The cooling systemThe condenserThe condenser is the “cooler“ of the air conditioner. Design of condenser The condenser comprises a tube coil which is securely attached to fins creating a large cooling surface which facilitates heat transfer. The condenser cooled by the cooling fan after the air conditioner is switched on in order to ensure that the refrigerant is circulated. The condenser is always installed upstream of the cooler. This increases the efficiency of the condenser. Heat is exchanged in the condenser through air cooling. The air is cooled by the headwind and by the cooling fan – an auxiliary fan may still be in use depending on type. The fan usually starts up when the air conditioner is switched on. This is not the case if pressure sender G65 is fitted; in this case, fan switch-on will then be delayed until a specific pressure is reached. Impurities in the condenser reduce air flow and can also impair condenser capacity and engine cooling. Function of condenser Hot, gaseous refrigerant coming from the compressor at a temperature of approx. 50 70 oC is injected into the compressor. The tubes and fins of the condenser absorb heat. Cool ambient air is ducted over the condenser, absorbing heat in the process and thereby cooling down the refrigerant. When the refrigerant cools down, it condenses at a specific temperature and pressure and becomes a liquid. At the bottom of the compressor, the refrigerant emerges from the condenser as a liquid.208_023Condenser CoolerAmbient air, heatedHot, gaseous refrigerantAmbient air, cool Cooling fanLiquid refrigerant208_024The condenser is often referred to as “liquefier“ in regard to its working method.22The fluid container and drierIn the refrigerant circuit with expansion valve, the fluid container serves as a refrigerant expansion tank and reservoir. Different amounts of refrigerant are pumped through the circuit when operating conditions such as the thermal load on the evaporator and condenser and compressor rpm are variable. The fluid container is integrated in the circuit in order to compensate for these fluctuations. The drier binds chemically moisture which has entered the refrigerant circuit during installation. The drier can absorb between 6 and 12 g of water, depending on type. The amount of water that can be absorbed is temperature-dependent. The amount of water absorbed increases as the temperature drops. Abraded material from the compressor, dirt arising from installation work and similar is also deposited. Function The liquid refrigerant coming from the condenser enters the container at the side. The refrigerant is collected in the container, then it flows through the drier and along the riser to the expansion valve in an uninterrupted flow containing no bubbles.208_026To expansion valveDrierThe fluid container is replaced every time the refrigerant circuit is opened. The fluid container must be kept closed as long as possible prior to installation in order to minimise absorption of moisture from the ambient air in the drier.208_025From condenserFilter strainer23The cooling systemExpansion valveThe expansion valve is the point where the refrigerant in the evaporator expands and cools down. It forms the interface between the highpressure side and low-pressure side of the refrigerant circuit. The expansion valve is used to regulate the refrigerant flow to the evaporator – in dependence upon the temperature of the refrigerant vapour at the evaporator outlet.– No more refrigerant than is necessary to maintain a steady “refrigerating climate“ in the evaporator is expanded in the evaporator. The closed control loop The refrigerant flow is controlled by the expansion valve in dependence upon temperature.Thermostat with sensor line and refrigerant208_022P Fü– When the temperature of the refrigerant Membranes leaving the evaporator rises, the refrigerant in the thermostat expands. The flow rate of the refrigerant to the evaporator at the globe To compressor (low valve increases. pressure) – When the temperature of the refrigerant leaving the evaporator drops, the refrigerant volume in the thermostat decreases. The flow rate to the evaporator at the globe valve is reduced. There are three forces at play in the thermostatic expansion valve:Globe valveP SaFrom evaporator (low pressure)From condenser (high pressure)To evaporator (low pressure)P Fe1. The pressure in the sensor line is dependent on the temperature of the superheated refrigerant. This pressures acts upon the membrane as an opening force (P Fü). 2. The evaporator pressure (PSa) acts upon the membrane in the opposite direction. 3. The pressure exerted by the regulating spring (PFe) acts in the same direction as the evaporator pressure.Regulating spring208_015The expansion valves are set. Their settings may not be altered. Do not bend the sensor line, because it is filled with a special gas.24Expansion valve – new generationThis expansion valve is also positioned between the high-pressure side and low-pressure side of the refrigerant circuit directly upstream of the evaporator.To compressor (low pressure)Evaporator outlet (low pressure) MembranesThermal head with special gas filling Pressure-equalising hole From condenser (high pressure)Push rodTo evaporator (low pressure)208_017Regulating springGlobe valveThe expansion valve is heat-controlled. It has a control unit with a thermal head and a globe valve. The thermal head on one side of the membrane has a special gas filling. The other side is connected to the evaporator outlet (low pressure) via pressure-equalising holes. The globe valve is push rod actuated. The pressure of the special gas, and therefore also the amount of refrigerant injected, is dependent upon the temperature on the lowpressure side.The expansion valve is always fitted with thermal insulation.Fitting the valve without thermal insulation will alter the set control characteristic.25The cooling systemA increase in cooling load increases the temperature at the evaporator outlet causing the pressure (pa) of the gas filling in thermal head to risepaThe globe valve cross-section is enlarged via diaphragms and the push rod. Refrigerant flows to evaporator and absorbs heat at the transition from high pressure to low pressure Heat is extracted from the air flowing through the evaporator208_018208_019When the temperature of the refrigerant at the evaporator outlet drops, the pressure (pb) in the thermal head dropspb208_020The cross-section of the globe valve, and therefore also the flow rate to evaporator, will again be reduced.208_021The valve opening ratio is dependent upon the temperature at the evaporator outlet (low pressure). Pressure equalisation is controlled.26The evaporatorThe evaporator operates according to the same principle as a heat exchanger. It is an integral part of the air conditioner in the heater box. When the air conditioner is switched on, heat is extracted from the air which flows through the fins of the cold evaporator. This air is cooled, dried and cleaned in the process.Refrigerant return line (gaseous state) Refrigerant supply line (vapour state)208_029Tubular evaporator208_030Function The refrigerant released by the expansion valve expands in the evaporator, cooling the evaporator down considerably. The refrigerant becomes a gas (boiling point). When the refrigerant in the evaporator boils, the temperatures are well below the freezing point of water. The refrigerant extracts the heat required for evaporation from its surroundings – which is the air flowing through the evaporator in this case. This air is channeled into the passenger cabin in a “cooled" state. Moisture in the cooled air collects at the evaporator in the places where the air temperature drops below the dewpoint temperature, i.e. it condenses. Condensation water is produced. The air is “dried“. This improves the climate and air quality inside the vehicle noticeably. Deposits of matter suspended in the air build up at the evaporator in addition to moisture. The evaporator also "purifies" the air.Pools of water below a stationary vehicle (condensation) are therefore not an indication of a fault.27The cooling systemRefrigerant circuit with restrictorIH GFWorking pressure HD = high pressure ND = low pressure Schematic diagram of a refrigerant circuit with restrictorND HDEH208_034IABCD1 D BA21 MPa = 10 barCPressures and temperatures in the circuit1Compression ratio Max. pressure 2 MPa (20 bar) Max. temperature 70 oC2Condensation Max. pressure 2 MPa (20 bar) Temperature reduction: approx. 10 oC28Legend High pressure Low pressureThe component parts: A B C D E F G H I Compressor with magnetic clutch Low-pressure switch Condenser High pressure service connection Restrictor Evaporator Low-pressure switch Low-pressure service connection Collecting tankG3 4 E F208_007In contrast to the circuit with expansion valve, the liquid refrigerant is injected into the evaporator through a restrictor. In restrictor-regulated air conditioners, a collecting tank is fitted at the low-pressure side in place of the fluid container on the high-pressure side. This collecting tank serves as a reservoir and protects the compressor (fluid shock). Also refer to page 31.All other components are identical to those used in the circuit with expansion valve. Additional connections for service work or sensors for monitoring functions can be integrated in the circuit, depending on circuit design and necessity. The pressures and temperatures are dependent upon the momentary operating state of the refrigerant circuit. The specified values are achieved after a specific period depending on the ambient temperature (refer to Workshop Manual).3Expansion from 2 MPa (20 bar) to 0.15 MPa (1.5 bar) Temperature: from 60 oC to –4 oC4Evaporation Max. pressure 0.15 MPa (1.5 bar) Temperature: –4 oC1208_03329The cooling systemThe restrictorThe restrictor is a narrowing in the refrigerant circuit located directly upstream of the evaporator. This narrowing “restricts“ the flow of the refrigerant. The refrigerant is warm under high pressure upstream of the restrictor. The pressure of the refrigerant drops rapidily when it passes the restrictor.208_035The refrigerant is cold at low pressure. The restrictor is therefore the “interface“ between the high-pressure and low-pressure sides of the refrigerant circuit. A seal ensures that the refrigerant only passes the restrictor at the narrowing. Tasks – To determine the flow rate of the refrigerant by means of a calibrated bore. The amount of refrigerant which can flow through this bore is limited by the pressure in the refrigerant circuit. – To maintain the pressure on the high-pressure side of the refrigerant circuit and keep the refrigerant in a liquid state when the compressor is running. – The pressure in the restrictor drops. The refrigerant cools down before it enters the evaporator through partial evaporation. – Atomisation of the refrigerant. The restrictor has a dirt strainer upstream of the narrowing. A strainer for atomising the refrigerant before it reaches the evaporator is located downstream the narrowing.To evaporatorStrainer for atomising the refrigerantCalibrated boreDirt strainer 0-ring, seals the high-pressure side off from the low-pressure side208_016Please note the installation position! The arrow on the restrictor points to the evaporator.30The collecting tankThere is a collecting tank in the low-pressure part of air conditioners with restrictor. This tank is installed in a warm location in the engine compartment (post-evaporation). It serves as an equalising vessel and reservoir for the refrigerant and refrigerant oil and also protects the compressor. The gaseous refrigerant coming from the evaporator enters the tank. If there are traces of moisture in the refrigerant, they are bound in the integrated drier. The refrigerant collects in the upper part of the plastic cap and is certain to be in a gaseous state when it is drawn in by the compressor through the U-tube. As a result, the compressor draws in gaseous refrigerant only, and no liquid droplets. Protection of the compressor against damage is thereby ensured. The refrigerant collects at the base of the collecting tank. The refrigerant drawn in by the compressor absorbs refrigerant through a hole in the U-tube. A filter strainer prevents the ingress of impure refrigerant through this hole.208_036Intake point for gaseous refrigerant Plastic capFrom evaporatorTo compressorDrierThe collecting tank must be kept closed as long as possible prior to installation (leave the sealing plugs on the connections) in order to minimise moisture absorption from the ambient air in the drier.U-tube Filter strainer Hole for refrigerant208_03731System control11097 68 2 45 3 t° pAn air conditioner will only function if all system components are working properly. Failure of one of these components could cause the working pressures to change. In this case, it is not possible to rule out consequential damage to the system and the engine. To avoid this, there are monitoring devices in the refrigerant circuit. A control unit processes the signals from the monitoring devices and controls the periodic switch-off and switch-on of the compressor and the speed of the fan. This ensures that the pressure level in the refrigerant circuit always adapts itself to the normal values. In systems equipped with an open-loop compressor, the signals from the monitoring device are also used for adaptation to demand for cooling. (switch-on and switch-off the air conditioner in accordance with demand for refrigeration. Icing of the evaporator is avoided at the same time.) The diagram shows the basic layout of the air conditioner. 32208_054The air conditioner does not necessarily have to have all the components shown in the diagram. Neither do these components have to be connected in this way. The diagram shows the system control of a simple manual air conditioner. 1 2 3 4 5 6 7 8 9 10 Air conditioner switch Pressure relief valve at compressor Radiator fan Air conditioner pressure switch Coolant temperature sender Radiator fan thermo switch Evaporator temperature sender Fresh air blower Engine control unit Magnetic clutch Air conditioner control unit (and/or radiator fan control unit, depending on system type)30 15 X 3130 15 X 31SJ 257 E 35J 257J 301 J 32 A F 18-t°t1t2G 153G 62 N 25p2p1F 129MV7 J 1013131208_055t° pBattery Air conditioner switch Radiator fan thermo switch t1 = 95 oC t2 = 103 oC F129 Pressure switch for air conditioner P1 = 0.2 MPa (2 bar)/3.2 MPa (32 bar) P2 = 1.6 MPa (16 bar) G62 Coolant temperature sender G153 Evaporator temperature sender J32 Air conditioner relay J101 Radiator fan 2nd speed relay J257 Mono-Motronic control unit J301 Air conditioner control unit N25 Air conditioner magnetic clutch V7 Radiator fan S Fuse A E35 F18Simple functional example showing how the compressor (via magnetic clutch N25) and radiator fan are switched on and off.Colour codes: Positive Negative Input signal Output signal Bidirectional signalIn the new-generation air conditioners, there is a high pressure sender in place of the pressure switch for air conditioner (refer to page 36).33System controlComponents of the safety systemsAir conditioner switch E35 Switch for switching on the air conditioner – the magnetic clutch makes the connection to the compressor. In automatically controlled systems, the radiator fan and the fresh air blower start simultaneously. In manual air conditioners, the fresh air blower must be switched to the 1st speed. A signal indicating that the air conditioner has been switched on is transmitted to the engine control unit, and engine idling speed is increased (to compensate for load resulting from compressor work). The switch may be located downstream of an ambient temperature switch. This ensures that the air conditioner cannot start when the temperature is below 5 °C. The valve (previously: bursting seal) is attached directly to the compressor or fluid container. The valve opens at a pressure of approx. 3.8 MPa (38 bar) and closes when the pressure drops (approx. 3.0 - 3.5 MPa/30 - 35 bar). Depending on type, a plastic disc which ruptures as soon as the valve lifts can be attached. In this case, the cause of the excess pressure in the system must be determined. The bursting seal should only be replaced when the system is empty.208_056208_068Pressure relief valvet° pEvaporator temperature sender G153The evaporator temperature sender measures the temperature between the cooling fins of the evaporator. The sender signal is transmitted to the air conditioner control unit. When the evaporator temperature drops too low, the compressor is switched off. The compressor is switched off at approx. –1 °C to 0 °C and switched on at approx. +3 °C Icing of the evaporator by freezing condensation water is prevented. In some systems, evaporator temperature switch E33 is used in place of this sender. The power supply to the magnetic clutch is opened directly by means of this switch. Other systems control this function by means of an ambient temperature switch.208_06134Pressure switch F129To monitor and/or limit the pressure conditions in the closed refrigerant circuit, high-pressure and low-pressure switches are installed on the high pressure side. If unacceptable pressures build up inside the system, the compressor will be switched off via the magnetic clutch. The pressure switch can be directly integrated in the line or attached to the fluid container. Pressure switch F129 is a 3-way combination switch for: – safeguarding the cooling air flow (fan circuit) – safeguarding the pressure conditions.208_057The pressure switch operates in the following conditions: – it switches off the magnetic clutch via the air conditioner control unit at an excess pressure of approx. 2.4 to 3.2 MPa (24 to 32 bar). This excess pressure can be caused by a dirty condenser, for example.p 3,2 MPa =208_058t° pp 0,2 MPa =208_059– it switches off the magnetic clutch via the air conditioner control unit when the pressure drops below a minimum value (0.2 MPa/ 2bar) . This can be caused by loss of refrigerant, for example.p 1,6 MPa =208_060– it switches the fan one speed higher at 1.6 MPa (16 bar) excess pressure. As a result, condenser performance is optimised.35System controlHigh pressure sender G65 – A new generation of senders for monitoring the refrigerant circuit. – Air conditioner pressure switch F129 has been replaced by an electronic pressure sensor. The evaluation electronics in the air conditioner and engine control units have been adapted accordingly. – Like pressure switch F129, the high pressure sender is integrated in the high pressure line. It registers the refrigerant pressure and converts the physical quantity of pressure to an electrical signal. Unlike the air conditioner pressure switch, the sender registers not only the defined pressure thresholds, it also monitors the refrigerant pressure throughout the working cycle. These signals indicate the load being exerted on the engine by the air conditioner and the pressure conditions in the refrigerant circuit. The next higher stage of the cooling fan and the magnetic clutch of the compressor are activated and deactivated via the radiator fan control unit.208_062Signal utilisation in the engine control unit in the radiator fan control unitt° pSubstitute functionIf the radiator fan control unit fails to detect any signals, then the compressor will be switched off for safety reasons. – The idling speed of the engine can be adapted exactly to the power consumption of a specific compressor. – The radiator fan speed activation and deactivation cycles are staggered with a short time delay. As a result, changes in the speed of the cooling fan are barely perceptible at idling speed. This enhances comfort especially in vehicles with engines with low power outputs. The fault in the high pressure sender is stored to the fault memory of the e n g i n e e l e c t r o n i c s .AdvantagesSelf-diagnosis “fault message“e.g.: 00819 high pressure sender G65 “Signal too low“36Function of high pressure sender2V/Div 5ms/DThe refrigerant pressure is applied to a silicon crystal. Depending on the pressure level, the crystal will be more or less “deformed“. The silicon crystal, together with a microprocessor, is integrated in the sensor and supplied with voltage. One of the properties of the silicon crystal is that its electrical resistance changes when it is deformed. Depending on the pressure characteristic, a test voltage picked off at the silicon crystal also changes as a result. The test voltage is conducted to the microprocessor and converted to a pulse-width modulated signal (A = pulse width, B = signal distance). At a low pressure, the crystal undergoes minimal “deformation". The voltage applied is therefore only opposed to a low electrical resistance. The voltage change is small.A0 B208_109At low pressurePulse-width modulated signal Microprocessor Voltage Test voltage Silicon crystal (resistance)208_063t° pPulse width signalThe microprocessor of the high pressure sender outputs a small pulse width at low pressures. Pulse width signals are generated at a frequency of 50 Hz per second. This is equivalent to a period duration of 20 ms = 100%. At a low pressure of 0.14 MPa (1.4 bar), the pulse width is 2.6 ms. This is equivalent to 13% of the period duration.208_064Period duration 20 msPulse width 2.6 ms37System controlAt high (increasing) pressure At high (increasing) pressure, the crystal is “deformed“ more, so the change of resistance is larger. The test voltage decreases proportionately.Pulse-width modulated signal Microprocessor Voltage Test voltage Silicon crystal (resistor)208_065t° pPulse width signalThe pulse width increases in proportion to the increasing pressure. At a high pressure of 3.7 MPa (37 bar), the pulse width is 18 ms. This is equivalent to 90% of the period duration.Pulse width 18 msPeriod duration 20 ms208_066Using the digital memory oscilloscope of the new vehicle diagnosis system VAS 5051, it is possible to visualise the pulse width signal.38Disconnected safety switch in the refrigerant circuit with restrictorIn the refrigerant circuit with restrictor, the low pressure and the high pressure are often monitored by two separate safety switches. Low pressure Air conditioner low-pressure switch F73 switches off the compressor when the pressure drops below approx. 0.17 MPa (1.7 bar) in the refrigerant circuit, for example. (This pressure drop can occur if the refrigerant level in the circuit is too low. The compressor is protected.) High pressure Magnetic clutch high-pressure switch F118 switches off the compressor when the pressure exceeds approx. 3.0 MPa (30 bar) for example. The absolute values should always be regarded as being system-specific.F73F118208_067Coolant temperature switch with pilot lampThe compressor constitutes an additional load for the engine. To avoid overheating the coolant when the engine is under heavy load, e.g. when travelling uphill, the additional compressor load is switched off. For this purpose, the coolant temperature is monitored additionally by a coolant temperature switch with a pilot lamp. (The primary monitoring device is the coolant temperature sender with indicator lamp in the dash panel insert.) The compressor cuts out at approx. 119 °C and cuts in at approx. 112 °C. Various switches with pilot lamp are used depending on vehicle type, e.g. F18 - Radiator fan thermo switch F163 - Air conditioner cut-off thermo switch.t° p208_069In vehicles with extended electronic sensor evaluation via the control unit combination of the vehicle, this additional check is no longer necessary. The signal generated by the primary monitoring device is utilized.39Cooling fan circuitCircuit connecting fan to engine/ condenser cooling systemshown using the VW Golf/Audi A3 as an example Fan operation is a basic condition for proper functioning of an air conditioner (refrigerant circuit) and the engine (coolant circuit). Condenser performance will be impaired if there is no cooling. Proper functioning of the air conditioner is no longer assured. In air conditioning, a second or third fan is often also used. These fans provide the necessary fresh air flow through the radiator and condenser. The fan control regulates radiator fan control unit J293 depending on the temperature of the coolant and the pressure in the refrigerant circuit. The absolute values are always vehicle-specific!Cooling fan1st auxiliary fan2nd auxiliary fanRadiator fan control unit J293Thermo switch F18Air conditioner pressure switch F129Example: Check functionsExample: 2-fan combination – The air conditioner is switched on, therefore the compressor is switched on and the pressure in the refrigerant circuit is greater than 0.2 MPa (2 bar). = both fans run at speed 1 – High pressure in the refrigerant circuit is greater than 1.6 MPa (16 bar) and/or coolant temperature is above 99 oC = both fans run at speed 2 – If the pressure in the refrigerant circuit drops below 1.6 MPa (16 bar) and the coolant temperature is below 99 oC = both fans will again run at speed 1 – When the engine is being operated without the air conditioner, only the cooling fan will be running. The fan will be running at speed 1 or 2 depending on coolant temperature.Coolant temperature The signal generator is radiator fan thermo switch F18. The thermo switch is located in the vehicle radiator. Speed 1 ON 92 .. 97 oC OFF 84 .. 91 oC Speed 2 ON 99 .. 105 oC OFF 91 .. 98 oCPressure in refrigerant circuit The signal generator is air conditioner pressure switch F129 or the high pressure sender G65. F129 switches the fan(s) to speed 2at a pressure of approx. 1.6 MPa (16 bar) (also refer to page 35).40Radiator fan control unit J293The radiator fan control unit is integrated in the vehicle control system. Incoming signals in the basic version: – from thermo switch F18 – from pressure switch F129 – from operating and display unit E87 (with automatic air conditioner) Tasks To convert the incoming signals – To switch the cooling fan on and off – To switch the compressor magnetic clutch on and off. Expanded functions of a new generation: Radiator fan control unit J293 has been developed technically and adapted functionally to the new high pressure sender G65. New generation It is fitted together with the high pressure sender and, as a distinguishing feature, has modified plug connections. The control unit evaluates the pulse-width modulated signal from the high pressure sender. The overall pressure range of the refrigerant pressure is monitored continously in this way. Functions There are also circuit variants where the functions of the control units are assumed by an air conditioner control unit. Integration in their control system is always vehicle-specific. For details, please refer to the current flow diagram. – To switch the radiator fan speeds and the magnetic clutch of the air conditioner compressor on and off – Bidirectional signal interchange with the engine and gearbox control unit – Monitoring the coolant temperature – with timer module for activating coolant runon pump V51 (e.g. 1.8-ltr. 5 V engine 165 kW)208_07041Temperature controlManual controlEvaporator Fresh-air flow Fresh air blower Refrigerant circuit Temperatureadjusted interior airCondenserHeat exchanger208_075Why temperature control? – The fresh-air flow cooled down at the evaporator is pumped into the passenger cabin by means of the fresh air blower. – This air is usually cooler than necessary (blower capacity is designed for maximum cooling, however the prevailing ambient temperatures are usually moderate). – To attain a pleasant interior temperature, a portion of the cold fresh air flow is therefore ducted over the heat exchanger the heating system and heated up. – Temperature fluctuations can also be caused by different ambient temperatures, road speeds, coolant temperatures, fresh air supplies etc. – In the case of simple manual air conditioners, the driver has to regulate the temperature.What is regulated? – Registration of actual values, i.e. temperature sensing. – Setpoint/actual value comparison, i.e. the driver performs an individual evaluation. The driver defines the comfort temperature, i.e. whether too warm or too cold. – Based on the evaluation, the driver decides whether • the temperature needs to be adjusted • in what direction • by how much and makes this adjustment manually. The driver is, in the figurative sense, both the controller and the actuator. The driver adjusts the temperature flap.42Automatic controlFresh air intake duct temperature sensorSunlight penetration senderDash panel temperature sensorControl unitAmbient temperature sensorFootwell vent temperature sender208_076Automatic air conditioners relieve the driver of this task. They have the advantage that they can include many more parameters in the control system and calculate the thermal result of your adjustment in advance. Various names are used to describe electronic air conditioner controls: – Digital temperature control – Climatronic – Air conditioner with automatic control What they all have in common is: – a control unit – ambient temperature sensor (one or two) – interior temperature sensor – additional senders (not in every system), e.g. sunlight penetration sender – Positioning motors on the heater/air conditionerThe diagram shows the positions of the sensors. The digital control unit is the master station. It processes all input signals from the sensors (information sender), interference-suppresses them and feeds them to the microcomputer in the control unit. The microcomputer calculates the output signals in accordance with the pre-programmed setpoints. The output signals are fed to the actuators via output stages. The actuators are the positioning motors on the heater/air conditioner. Suitable positioning motors are assigned to the flaps. Air conditioners of the current generation are linked to other vehicle control units either directly or via the CAN-BUS. Information on road speed, on engine speed and on ´time parked´ are also included in the evaluation of the air conditioner control unit in this way. 43Temperature controlSystem overview of an electronically controlled air conditioner(the temperature is regulated evenly at the left- and right-hand sides of the passenger cabin as shown using the Golf as an example. An identical system is used in the Audi A3) Sensors (for system control and temperature control)Sunlight penetration photo sensor G107 Temperature sensor Dash panel Temperature sensor G56 Blower V42CLIMAtronicAUTOECONCLIMATAmbient temperature sensor G17Temperature sensor Fresh air intake duct temperature sensor G89Footwell vent temperature sender G192Air conditioner pressure switch F129Auxiliary signals: road speed signal engine speed signal 'time parked' signalv n thCoolant temperature warning switch (overheating) F14Radiator fan thermo switch F1844Actuators (for system control and temperature control)Footwell/defroster flap positioning motor V85 with potentiometer G114 Climatronic control unit J255 and Air conditioner/Climatronic operating and display unit E87 Central flap positioning motor V70 with potentiometer G112IMATRONICAUTOECOTemperature flap positioning motor V68 with potentiometer G92NAir flow flap positioning motor V71 and air recirculation flap with potentiometer G113Fresh air blower Control unit J126 and fresh air blower V2Auxiliary signals: engine control unit control unit with display unit in dash panel insertDiagnosis plug connection T16Magnetic clutch N25Radiator fan control unit J293208_077Radiator fan, right V7 and auxiliary fan V3545Temperature controlControl unit with operating and display unitControl unit208_078O AUTCLIMO ATRNICECONECONAUTOFFO208_102208_101Dash panel temperature sensor G56 Climatronic control unit with operating and display unitOperating and display unit E87Dash panel temperature sensor G56 Control unit with operating and display unit of Audi TT CoupéDesign The control unit is combined with the operating and display unit which is adapted to the design of the vehicle in question. A vehicle interior temperature sensor is also integrated in the control unit. Function The control unit receives information from the electrical and electronic components (sensors). These signals are processed by the control unit in accordance with the setpoints. The output signals of the control unit then control the electrical actuators. The control unit is equipped with a fault memory. Failure of a component or an open circuit can be detected quickly via the self-diagnosis. No matter what fault occurs, the control unit will remain in operation and maintain the temperature settings in emergency mode.46Actuators/sensors on a heater/ air conditionerFresh air intake duct temperature sensor Footwell/defroster flap positioning motorAir flow flap positioning motor and air recirculation flapFresh air blowerFresh air blower control unitFootwell vent temperature senderTemperature flap positioning motor (concealed)Central flap positioning motor208_079A positioning motor is assigned to each flap for air ducting in the heater/air conditioner. The air flow flap and air recirculation flap are driven by a positioning motor. These flaps are adjusted separately by a driving pulley with two guide rails. In other systems, the air recirculation flap can also be adjusted by means of vacuum and solenoid valves.In this case, the fresh air blower and fresh air blower control unit are separate components. However, they can also be combined to a unit.47Temperature controlThe main temperature sensorsAmbient temperature sensor G17 The temperature sensor is positioned in the vehicle front section. It registers the actual ambient temperature. Signal utilisation The control unit controls the temperature flap and the fresh air blower in dependence upon the temperature. Effects of signal failure If the signal fails, the measured value of the second temperature sensor (temperature sensor in fresh air intake duct) is utilised. If this signal also fails, the system continues to operate by assuming a substitute value of +10 oC. Air recirculation is not possible. The temperature sensor has self-diagnostic capability. Fresh air intake duct temperature sensor G89 The temperature sensor is located directly inside the fresh air intake duct. It is the second actual ambient temperature measuring point. Signal utilisation The control unit controls the temperature flap and the fresh air blower in dependence upon the temperature. Effects of signal failure If the signal fails, the measured value of the first temperature sensor (ambient temperature sensor) located in the vehicle front section is utilised. The temperature sensor has selfdiagnostic capability. Both temperature sensors always process the lowest value.208_082208_08148Dash panel temperature sensor G56 with temperature sensor blower V42 The temperature sensor is usually integrated directly in the control unit and transfers the actual interior temperature to the control unit. It is located in the air stream of a fresh air blower which is used to draw off interior air. The fresh air blower is activated by the operating and display unit. It draws off the interior air in order to avoid measurement errors at the temperature sensor. Signal utilisation