Renault APV Training on AC Cold Loop

Air conditioning - Cold loop

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1

CONTENTSIntroduction 4

Environment and Safety 6Creating a cold loop 10RENAULT cold loops 18

Maintenance of the cold loop 38Questionnaire 67

3

INTRODUCTIONAir conditioning - Cold loop 5

4

Introduction

Air conditioning - Cold loop

NOTEThe information and specifications detailed in this document are a generalreference to a specific configuration. As this rule does not apply to allvehicles, it is essential to refer to the documentation corresponding tothe vehicle before carrying out any maintenance operations.

5

ENVIRONMENT ANDSAFETY

Environmental impact 7Safety instructions 9

6

Environment and Safety

Environmental impactEnvironmental impact of R134a hydrofluorocarbon (HFC) emissions

A vehicle emits an average of 30 tons of CO2 during its life.

When 700 grams of HFCs (R134a) are released into the atmosphere, this is theequivalent of 1 ton of CO2, in other words an environmental impact 1300 timesgreater than that of the CO2.

Although it is a greenhouse gas, CO2 is much less potent than HFCs.

The prospect of a growth in the number of vehicles (according to current assump-tions) has another direct consequence: a significant increase in the number ofair-conditioned vehicles.

Figure 1. Protection of the environment.

HFCs have a high potential for atmospheric warming and the significant growthin the number of air-conditioned vehicles indicate that there is a major risk of in-creasing the greenhouse effect.

These excess emissions of pollutants resulting from vehicle air-conditioning aremaking a serious contribution to global warming.

This alarming fact means that we must be aware of the environmental conse-quences of any kind of HFC emissions.

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In order to limit the possibility of releasing refrigerant gases into the atmosphereas far as possible, it is essential to strictly adhere to the procedures contained inthe technical documentation.

Working on a vehicle air-conditioning system

Operations on a cold loop means that the following rules must be observed:

• You must be trained in operations on the cold loop.

• You must be trained in using and maintaining the charging station.

• You must be informed regarding refrigerant handling and storage conditions.

• You must never release refrigerant into the atmosphere.

• You must never open a circuit whose pressure is not equal to or less than 0 bar.

• You must observe the refrigerant recovery and recycling procedures.

• You must always carry out a search for leaks after any cold loop maintenanceoperation.

8


Safety instructionsIt is essential to follow the safety instructions (figure 2) when working on an air-conditioning circuit.

Figure 2. Safety instructions

The safety instructions are as follows:

• Wear gloves.

• Wear protective glasses.

• Work in a well ventilated area.

• Do not weld or heat to more than 100 degrees Celsius.

• Do not smoke.

• Do not leave the circuit open to the air or you will have to replace the dehydrat-ing canister.

IMPORTANT

Before any operation, refer to the technical documentation and follow thesafety instructions contained in it.

9

CREATING A COLDLOOP

The method of producing cold air 11Making a cold loop 14

10

Creating a cold loop

The method of producing cold airRole of air conditioning

The role of air-conditioning in a vehicle is to maintain the comfort of the occupants(figure 3).

Figure 3. Comfort inside a vehicle.

Comfort depends principally on the following parameters:

• noise level,

• absence of odours,

• temperature,

• the level of humidity,

• the speed of air circulation in the passenger compartment.

In cold weather, the air conditioning lowers the level of humidity in the passengercompartment and helps to demist the windows.

In warm weather, the air conditioning cools the passenger compartment.

11


Physical attributes

Matter appears in three states: solid, liquid and gas.

Cold production exploits the two physical attributes accompanying a change instate of matter.

• The change from the liquid state to the gaseous state is evaporation.

• The return from the gaseous state to the liquid state is condensation.

Illustration of how pressure affects a liquid

Rapid expansion of a fluid under pressure produces cold. The greater the pressuredifference, the greater the cold production.

As an example, pressing the trigger of a fire extinguisher releases carbon dioxideunder pressure. The pressure changes suddenly from 50 to 1 bar.

This rapid fall in pressure creates carbon dioxide foam and produces cold (fig-ure 4).

Figure 4. Expansion.

12


Illustration of the effect of the evaporation of a liquid

The faster the evaporation, the greater the sensation of cold. Evaporation of afluid absorbs heat.

If you pour water, petrol or ether in turn on to your hand (figure 5), the ether evap-orates fastest and gives the greatest sensation of cold.

Figure 5. Evaporation of liquids.

The cold loop therefore uses a highly volatile fluid.

13


Making a cold loopTheoretical cold loop.

The expansion phenomenon in a cold loop is produced using a reservoir of fluidunder pressure, fitted with an outlet expansion valve (figure 6).

The greater the expansion, the greater the cold production.

Figure 6. Reservoir of fluid with expansion valve.

A liquid-gas mixture coming from the expansion valve passes through an evapo-rator (figure 7) to absorb the heat from the surrounding environment.

Figure 7. Reservoir with expansion valve and evaporator.

A gas is produced at the evaporator outlet. This gas must be recovered and recir-culated to complete the cold loop.

14


The gas enters the compressor then liquefies in the condenser before returning tothe reservoir (figure 8).

Figure 8. Complete theoretical cold loop.

The cold loop circuit is now complete.

15


Cold loop components

The main components of the cold loop in the vehicle (figure 9) are as follows:

• a compressor (1),

• a condenser (2),

• a reservoir (3),

• an expansion valve or a fixed orifice tube (4),

• an evaporator (5).

Figure 9. Components of the cold loop.

Cold loop temperatures and pressures

Knowing the outlet temperatures and pressures of the components is useful whensearching for cold loop malfunctions.

The cold loop pressures and temperature statuses are as follows:

Zone of low pressure system:

– very hot state (pipework in red),

– hot state (pipework in orange).

Zone of low pressure:

– very cold state (pipework in dark blue),

– cold state (pipework in light blue),

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A check of the pipework temperature is used to perform an initial diagnosis of circuitoperation (refer to maintenance of the cold loop, “Diagnosis by touch” section).

Summary of pressures and temperature by component

The compressorWhen leaving the compressor, the fluid is gaseous, very hot and under high pres-sure.

The condenserWhen leaving the condenser, the fluid is hot and under high pressure.

The dehydration canisterWhen leaving the canister, the fluid is liquid, hot and under high pressure.

The accumulator (depending on the type of cold loop)On leaving the accumulator, the fluid is gaseous, cold and under low pressure.

The thermostatic expansion valveOn leaving the thermostatic expansion valve, the fluid is gaseous, cold and underlow pressure.

The fixed orifice tube (depending on the type of cold loop)On leaving the fixed orifice tube, the fluid is very cold and under low pressure.

The evaporatorOn leaving the evaporator, the fluid is cold and under low pressure.

IMPORTANT

Certain parts of the pipework can become very hot. Risk of burns!

17

RENAULT COLDLOOPS

Air conditioning fluid 19The two types of cold loop used by RENAULT 20The components common to the two cold loops 22

The components specific to each cold loop 34

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RENAULT cold loops

Air conditioning fluidToday R134a refrigerant is used in all RENAULT vehicles for the production of coldair. R134a refrigerant replaced R12 refrigerant in 1993 for environmental reasons.

R134a is a hydrofluorocarbon with thefollowing properties (figure 10):

• ODOURLESS

• COLOURLESS

• NON-FLAMMABLE

Figure 10. Properties of the R134a fluid.

IMPORTANT

You must never mix R12 and R134a (figure 11).

Figure 11. Incompatibility of the R12 and R134a fluids.

It is only possible to convert a vehicle from R12 to R134a if the refrigerant circuitis converted.

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RENAULT cold loops

The two types of cold loop used by RENAULTRENAULT uses two types of cold loop for air-conditioning purposes (figure 12).

Figure 12. The two types of cold loop used by RENAULT.

The components and their function are similiar in both types of loop:

• Compression is provided by the compressor (1),

• Condensation is produced in the condenser (2),

• Expansion is provided by a thermostatic expansion valve (4a) or a fixed orificetube (4b),

• Evaporation is produced inside the evaporator (5),

• Filtration and a fluid reserve are provided by the dehydration canister (3a) orthe accumulator (3b).

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RENAULT cold loops

Cold loop using fixed orifice tube and accumulator

The configuration of the first type of cold loop (figure 13).

A fixed orifice tube (1) is locatedbetween the condenser outlet and theevaporator inlet.

The accumulator (2) is fitted to thelow-pressure circuit between theevaporator outlet and the compressorinlet.

Figure 13. Cold loop using fixed orifice tube.

Cold loop using thermostatic expansion valve and dehydration canis-ter

The second type of cold loop (figure 14) differs from the first one in two ways.

Figure 14. Cold loop using thermostaticexpansion valve.

1. The expansion valve (1) is of thethermostatic type and controlsthe expansion in relation to theevaporation.

2. The dehydration canister (2) isfitted in series in the high pressurecircuit between the condenser andthe thermostatic expansion valve.

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RENAULT cold loops

The components common to the two cold loopsThe role and the operation of components common to both cold loops.

Compressor

The compressor (figure 15) is the driving component in the circuit. It is driven byan accessories belt.

Figure 15. Compressor.

Role of the compressor

The compressor functions are as follows:

1. The compressor sucks in the gas.

2. The compressor delivers the gas to the condenser.

3. The compressor raises the pressure.

4. The compressor ensures the fluid circulates in the circuit.

IMPORTANT

Certain parts of the pipework can become very hot. Risk of burns!

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RENAULT cold loops

The compressor clutch

The compressor must not be driven continuously. An electromagnetic clutchmounted on the pulley of the compressor ensures circulation.

Figure 16. Compressor clutch.

The electromagnetic clutch (figure 16) consists mainly of the following compo-nents:

• a free turning pulley (1),

• a shaft (2),

• a moveable plate (3),

• an electromagnet (4).

The electrically operated electromagnet pulls the clutch plate against the free turn-ing pulley.

The free pulley engages with the compressor shaft.

All the internal components of the compressor are now driven.

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RENAULT cold loops

Two types of compressor

There are two types of compressor:fixed capacity and variable capacity.

Fixed capacity compressor

The fixed capacity compressor (figure 17) compresses a constant volume of gason each rotation.

Figure 17. Fixed capacity compressor

The level of refrigeration is regulated by alternately releasing or engaging the elec-tromagnetic clutch.

The fixed capacity compressor consists of the following main components: a shaft(1), a cam (2), an oscillating plate (3) and pistons (4).

Operation of the fixed capacity compressor

The compressor shaft, driven in rotation, turns the cam lobe. The cam lobe trans-fers its movement to the oscillating plate. At each rotation of the plate, the pistonsoscillate with a fixed movement, allowing intake and delivery of the fluid.

A set of valves synchronize the intake and outlet of the fluid allowing it to becomepressurized.

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RENAULT cold loops

Variable capacity compressor

The variable capacity compressor (figure 18) constantly adjusts the volume of gascompressed.

Figure 18. Variable capacity compressor

The variable capacity compressor consists of the following main components: ashaft (1), an oscillating plate (3) operated by a lever (2) and pistons (4).

Operation of the variable capacity compressor

Capacity is regulated by varying the angle of the oscillating plate which increasesor reduces the piston travel.

When there is a significant demand for cold air, the plate oscillates at its maximumangle and the volume of gas compressed is at its maximum.

When there is a low demand for cold air, the plate oscillates at its minimum angleand the volume of gas compressed is at its minimum.

REMINDERWhen leaving the compressor, the fluid is gaseous, very hot and underhigh pressure.

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RENAULT cold loops

Lubricating the compressor

The compressor is lubricated by an oil which is specific to the refrigerant and thetype of compressor.

The functions provided by the oil (figure 19) are as follows:

• lubricating the moving parts,

• helping to cool the compressor,

• helping filtration,

• increasing sealing.

Figure 19. Refrigerant oil.

The specifications of the oils used for each type of compressor can be found in thetechnical documentation.

IMPORTANT

The oil differs according to the refrigerant used and the type of compres-sor.

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RENAULT cold loops

Condenser

Role of the condenser

The role of the condenser (figure 20) is to dissipate heat accumulated during com-pression of the gas.

The condenser is located downstream of the compressor close to the radiator.

Figure 20. condenser.

Operation of the condenser

The condenser is made up of many parallel pipes.

The refrigerant is cooled and condensed as it passes through the condenser’sparallel pipes.

REMINDERWhen leaving the condenser, the fluid is hot and under high pressure.

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RENAULT cold loops

Cooling fans

Role of the cooling fans

One or two cooling fans (figure 21) mounted next to the condenser assist the con-densation process.

Figure 21. Cooling fans.

Operation of the cooling fans

The blower fan is placed in front of the condenser.

The pulling fan is placed behind the condenser.

The cooling fans have several speeds.

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RENAULT cold loops

Evaporator

Role of the evaporator

The evaporator (figure 22) is located downstream of the expansion valve and isincorporated into the passenger compartment air circuit.

Figure 22. Evaporator.

The evaporator causes evaporation of the refrigerant released by the expansionvalve.

Operation of the evaporator

A pulling fan sucks air through the evaporator.

As it evaporates, the refrigerant absorbs heat from the air drawn in from the pas-senger compartment.

The air drawn in emerges cold and its moisture condenses on the walls of theevaporator.

REMINDEROn leaving the evaporator, the fluid is cold and under low pressure.

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RENAULT cold loops

Cold loop safety components

The pressure sensor and the evaporator sensor are the cold loop safety compo-nents.

Pressure sensor

The refrigerant fluid pressure sensor (figure 23) is located in the high-pressurecircuit. The role of the pressure sensor is to continuously send information to thecomputer.

Figure 23. Pressure sensor

Evaporator sensor

The evaporator sensor (figure 24) is located on the fins at the coldest point of theevaporator.

Figure 24. Evaporator sensor

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RENAULT cold loops

The sensor’s role is to measure the temperature of the air pumped through theevaporator to prevent icing.

The evaporator sensor is present on all vehicles equipped with a fixed capacitycompressor and on some vehicles equipped with variable capacity compressors.

Cold loop inter-component connections

The cold loop also comprises pipes, unions fitted with O-rings and one or two fillervalves.

Pipes

The piping (figure 25) connects the different components and allows transfer ofthe fluid.

Figure 25. Two types of piping: rigid and flexible.

The cold loop includes rigid aluminium or steel pipes and flexible rubber hoses.

The gas circuit pipes have a large diameter and the liquid circuit pipes have a smalldiameter.

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RENAULT cold loops

Unions

The unions (figures 26 and 27) guarantee sealing and allow the circuit to withstandhigh pressures.

Figure 26. clip-secured connections.

Unions with clip-secured connections.

Clamp-secured unions.

Figure 27. Clamp-secured connections.

Figure 28. O-rings.

The unions are fitted with specialO-rings (figure 28).

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RENAULT cold loops

IMPORTANT

The O-rings must always be replaced with new ones when they are re-moved and be coated with compressor oil when being refitted.

Valves

The cold loop includes one or two charging valves (figure 29) with different diam-eters.

Figure 29. Charging valves.

The charging valves allow the charging station to be connected and venting of thecircuit.

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RENAULT cold loops

The components specific to each cold loopCold loop using fixed orifice tube and accumulator

Expansion valve with fixed orifice tube

Figure 30. fixed orifice tube.

The fixed orifice tube (figure 30) consists of:

• an inlet filter (1),

• a calibrated tube (2),

• an outlet filter (3).

Fixed orifice tube expansion valve operation

The refrigerant passes through the inlet filter, is partially vaporised in the calibratedtube and reappears through the outlet filter.

REMINDEROn leaving the fixed orifice tube, the fluid is very cold and under lowpressure.

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RENAULT cold loops

Accumulator

The accumulator (figure 31) is located upstream of the compressor on the low-pressure circuit.

Figure 31. Accumulator.

On entering the accumulator (1), the fluid is made up of oil and a refrigerant liq-uid/gas mixture.

Accumulator operation

1. The liquids (2) separate from the gas (3) under the effect of gravity.

2. The oil and the refrigerant are introduced into the circuit (4) via a specific tube.

3. The accumulator also filters the impurities, dehydrates the fluid and serves asa buffer reservoir.

REMINDEROn leaving the accumulator, the fluid is gaseous, cold and under lowpressure.

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RENAULT cold loops

Cold loop using a thermostatic expansion valve and dehydration can-ister

Thermostatic expansion valve

The thermostatic expansion valve (figure 32) is crossed by both the inlet circuit (1)and the output circuit of the evaporator (2).

Figure 32. Thermostatic expansion valve.

The thermostatic expansion valve continuously adjusts the quantity of fluid helddepending on its temperature at the evaporator outlet.

Thermostatic expansion valve operation

When the evaporator outlet temperature is high, the fluid in the thermostatic cap-sule (3) expands.

1. The ball (4) therefore completely opens the inlet circuit in the evaporator.

2. The fluid expansion increases. The evaporator outlet temperature falls.

When the evaporator outlet temperature is low, the fluid in the thermostatic capsulecontracts.

1. The ball therefore stops the passage of the fluid.

2. The production of cold air is stopped until the temperature at the outlet in-creases.

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RENAULT cold loops

REMINDERAt the thermostatic expansion valve outlet, the fluid is gaseous, coldand under low pressure.

Dehydration canister

The dehydration canister (figure 33) is located between the condenser and thethermostatic expansion valve.

Figure 33. Dehydration canister

The canister filters, dehydrates and serves as a buffer reservoir for the refrigerant.

Operation of the dehydration canister

The fluid (1) entering the canister consists of refrigerant liquid (2) and oil (3).

The operation of the dehydration canister is as follows:

1. The fluid falls in the canister due to gravity.

2. The oil/refrigerant mixture is filtered, dehydrated then returned to the circuit (4).

REMINDERAt the dehydrating canister outlet, the fluid is liquid, hot and under highpressure.

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MAINTENANCE OFTHE COLD LOOP

Verifying the efficiency of an air conditioning system 39Diagnosis by touch 44

Leakage test on the cold loop 46Maintenance of the air-conditioning system 52

Recovery of the refrigerant 57Vacuum extraction 60Charging the circuit 62

Conversion of an R12 air-conditioning circuit into an R134a circuit 64

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Maintenance of the cold loop

Verifying the efficiency of an air conditioning systemThe verification is made by checking the temperature of air coming from an air vent(figure 34).

Figure 34. Checking the temperature at an air vent.

Verification of the efficiency of the air-conditioning system involves five checkingstages:

1. Operation of the control panel

2. Cleanliness of the passenger compartment filter.

3. Battery voltage.

4. The efficiency check.

5. System identification

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Checking the control panel selections

The distribution and recycling controlsopen and close the flaps managing theair flow in the vehicle.

Figure 35. Control panel.

Each panel control (figure 35) mustproduce the desired effect.

1. Passenger compartment ventilation speed: all the speeds must be operational.

2. Air recycling: the control operates the flap and air is no longer taken in fromoutside the passenger compartment.

3. Distribution of air in the passenger compartment: The distribution of the airflowsmust vary according to the selected positions.

4. Air temperature distribution: with the engine warm, the control must vary thetemperature of the blown air.Note. With the distribution control in the "cold" position, it should not be possi-ble to feel warm air.

5. The A/C control and indicator light: operating the control must light the A/C onindicator light.Note. On most vehicles, one of the ventilation speeds must be selected for theA/C control to switch on the A/C on indicator light.

NOTEMalfunction of any of the panel controls may affect the performance of theair-conditioning circuit.

40


Cleanliness of the passenger compartment filter.

A clogged filter makes the air conditioning circuit less effective.

There are two types of filter (figures 36 and 37).

The first type is the particle filter.

This filter retains around 90% of thedust and pollen which usually entersthe passenger compartment.

The particle filter consists of a fibrousmedium producing an electrostaticeffect which acts as a magnet for dustand pollen.

Figure 36. The particle filter.

The second type also filters odours.

Figure 37. Particle and odour filter.

This particle and odour filter containsactive carbon which absorbs theexhaust gas odours and combustionresidue.

NOTERefer to the technical documentation and the vehicle servicing bookletto find out the type of passenger compartment filter and its replacementinterval.

41


Battery voltage

Checking the voltage consists of carrying out a full check of the battery in accor-dance with the procedure described in the technical documentation for the vehicle.

The stages of a complete battery check are as follows:

1. visual inspection,

2. charge check,

3. battery test using the tester.

Performance test

The efficiency check consists of measuring the temperature of the air coming outof an air vent in accordance with the procedure described in the technical docu-mentation for the vehicle.

Figure 38. Digital display thermometer.

This measurement is made using athermometer with a digital display(figure 38).

On most systems, the temperature measured at the air vent should be less than10°C for about one minute, for an outside temperature of 20°C.

Effect of humidity on the measurement

Measuring the efficiency of the air-conditioning system may be affected by a highoutside air temperature and moisture content.

Under these conditions, the temperature measured at the air vent may be greaterthan the correct value without the system efficiency being abnormal.

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NOTEAt a steady outside temperature, the higher the moisture content, thehigher the temperature measured at the air vent.

System identification

System identification confirms the performance check by a conformity check.

Identification of the air-conditioning system and the "Statuses and Parameters"test are performed using the diagnostic tool.

43


Diagnosis by touchDiagnosis by touch is a quick way of confirming a malfunction in the cold loop andcontinuing the diagnostic check in the right direction.

The diagnostic procedure usually leads to a performance test of an air conditioningsystem whose efficiency has not been established.

The procedure is applicable every time a diagnosis is carried out on the cold loop.

The method consists of comparing, bytouch, a temperature status (taken atdifferent points of the circuit) with anormal operating temperature status.

Figure 39. touch method.

The temperature status is verifiedupstream and downstream of eachcomponent in the cold loop (figure 39).

Temperature status test conditions

Before checking the cold loop using the touch method, the air-conditioning systemmust be placed under the performance test conditions (as described in the tech-nical documentation for the vehicle).

Pointing the diagnosis in the right direction using the touch method

The three stages for determining the incorrect temperature statuses and directingthe diagnostic procedure in the right direction are as follows:

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Stage 1. The testReferring to the normal temperature statuses, check (subjectively) whether thereis a difference of temperature by proceeding as follows:

1. By touch, verify the temperature status at the expansion valve inlet and outlet.

2. Verify the temperature status of the other components in the low-pressure sys-tem.

NOTEIf the temperature statuses in the low-pressure zone are correct, it is un-necessary to carry out tests in the high-pressure zone (very hot statuses).

Stage 2. Pointing the diagnostic procedure in the right directionDepending on the fault detected at the expansion valve, the diagnosis may bedirected in the following way:

• The temperature status is abnormal at the expansion valve "inlet" and "outlet:Check the temperature statuses upstream of the expansion valve up to thosecomponents whose temperature status is correct.Note. If the temperature statuses are consistent, the malfunction is located inthe high-pressure zone.

• The temperature status is abnormal at the expansion valve "inlet" and "out-let": Check the temperature statuses downstream of the expansion valve up tothose components whose temperature status is correct.Note. If the temperature statuses are consistent, replace the expansion valve.

• The temperature statuses are normal at the expansion valve "inlet" and "outlet".Note. If the temperature statuses are consistent, check the refrigerant fluidcharge.

NOTEAn abnormal temperature status can affect the temperature status of theother components in the circuit.

Stage 3. Working out the diagnostic procedureBy logical reasoning, based on the operating principle of each component in thesystem, it is possible to correctly direct the diagnostic method using the touchmethod.

45


Leakage test on the cold loopA leak in the cold loop can also affect the efficiency of the air conditioning circuit.

Leaks are detected by means of two detectors: the electronic detector (figure 40)and the tracer detector.

• The electronic detector emits an audible signal when refrigerant is present. Theelectronic detector should be used first.

• The fluorescent reactive tracer is used if the electronic detection fails.

Figure 40. Electronic detector.

An electronic detector is a measuringinstrument which should be handledwith care and regularly serviced.

Establishing the source of leaks using the electronic detector

The electronic detector is a specially designed measuring instrument for detectingleakage of different halogen gases.

Depending on the model, the electronic detector indicates the gas concentrationby emitting a variable frequency acoustic signal plus, depending on the model, avisual indication.

NOTEThe electronic detector only detects relatively large leaks.

46


A few recommendations for using an electronic detector:

• Ensure the measurement probe is compatible with the type of refrigerant gasto be detected.

• The measurement probe is a very sensitive component and must be protectedfrom dust and moisture and must not be brought into contact with oily or greasycomponents.

• The measurement probe must not be used without its protective endpiece.

• If the sensitive component of the probe is dirty, it must be cleaned or replaceddepending on the model.

• The measurement probe has a limited life.

• The condition of the battery power supply is normally indicated by an LED.

Technique for finding leaks

Two steps to detect the source of the leaks.

Stage 1. Equipment initialisationThe initialisation (calibration) of the equipment allows themeasurement (detection)threshold in the ambient environment to be adjusted.

To calibrate the electronic detector, refer to the equipment user manual and thetechnical documentation procedures.

The presence of gas is only indicated if its concentration exceeds that of the ambi-ent environment used for initialisation. The less the ambient environment is con-taminated, the greater the sensitivity of the detector.

NOTEThe initialisation method allows a reduction in reading errors due to thepresence of pollutants in the engine compartment.

47


Stage 2. Tracing leaksBefore starting the search, refer to the leak tracing table in the technical documen-tation.

Leak tracing consists of following (as closely as possible) the route of the circuitusing the probe (figure 41). The detector reacts to variations in the refrigerantconcentration (the higher the gas concentration, the higher the frequency of thedetector signal).

To refine the search, recalibrate the detector in the contaminated air.

Following the circuit route, try to detecta stronger concentration by referringto the signal and its frequency.

Figure 41. Detection technique.

Repeat the operation as often asnecessary until the source is located.

This method allows accurate location of the source of refrigerant gas leaks.

NOTEIf there are multiple sources, the search for minor leaks will be assistedby repairing the biggest leaks first.

48


Establishing the source of leaks using the tracer detector

Searching using the tracer detector is only valid if the air-conditioning system isoperational.

This detection procedure is to be used as a last resort in the case of “untraceableleaks” which cannot be revealed by the electronic detector.

The presence of dye in the refrigerantis verified using an ultraviolet lamp(figure 42) and strictly following theprocedure described.

Figure 42. Tracer detection kit.

Dye must not be injected into the cold loop if fluorescent traces appear.

49


Tracer leakage detection technique

Two steps to detect the source of the leaks.

Stage 1. Injecting dye into the circuitTo inject dye into the circuit, refer to the procedure in the technical documentation.

Figure 43. Tracer injection gun.

The dye must only be injected usingthe specified equipment (figure 43).

After injecting the dye, place a clearly visible label next to the charging valves,indicating the presence of dye in the circuit and the date of the injection operation.

IMPORTANT


50


Stage 2. Scan the circuit with an ultraviolet lampLeaks are detected by scanning the circuit using the ultraviolet lamp (figure 44).

To scan parts of the circuit which aredifficult to access, reflect the ultravioletlight using a mirror.

Figure 44. Ultraviolet lamp.

When searching for leaks using a tracer, the results will only appear after severalminutes or even several hours of circuit operation.

NOTEA leak from the evaporator may be detected by the presence of fluorescenttraces in the condensation.

51


Maintenance of the air-conditioning system

Figure 45. Maintenance of the air-conditioning system

REMINDERMaintenance operations on a cold loop require compliancewith the rulesfor environmental protection.

Servicing operations

It is recommended that certain servicing operations are carried out on the air-con-ditioning system. It is necessary to refer to the technical documentation for thevehicle to find out the servicing frequency.

As a general rule, the frequency of servicing operations is as follows:

Every year:

• Ensure that the condenser and radiator are clean.

• Ensure that air can circulate freely between the fins.

• Ensure that the cold air blower unit is not obstructed.

• Ensure that the condensation drains away correctly.

Every four years:

• Check the refrigerant charge.

52


Periodically

• To prevent possible odours, it may be necessary to treat the air-conditioningsystem after each winter or prolonged period of non-operation, .

NOTEChecking the refrigerant charge is associated with recovery of the refrig-erant.

It is only by this operation that the quantity of refrigerant in the circuit can bechecked.

Charging station

The charging station is used either for preventive maintenance or before openingthe circuit.

The charging station (figure 46) allows the following operations to be carried out:

1. Recover the oil and the refrigerantas discharging gas into theatmosphere is strictly prohibited.

2. Create a vacuum in the cold loop toeliminate maximum humidity andimpurities, check the sealing andprepare the charge.

3. Charge the circuit with oil andrefrigerant.

Figure 46. Charging station.

REMINDERBefore using the charging station, refer to its user manual.

Instructions regarding use

The charging station is a measuring instrument which uses an electronic weighingsystem. It must be handled with care (especially when being moved in the work-shop) and maintained regularly.

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Before connecting a charging station to the air-conditioning system, the followingoperations must be carried out:

• Check the quantity of refrigerant in the reservoir (must not exceed 80% of thereservoir capacity).

• Place a quantity of new oil sufficient for the operation in the topping up bottle(with internal tube).

• Drain or mark the quantity of used oil present in the oil drain bottle (withoutinternal tube).

• Verify that the two bottles are correctly connected to the charging station.

• Check that there is no error or maintenance message on the control panelscreen.

• Check the sealing of the external connections (tightness of pipes to the stationand to the quick release couplings).

• Ensure that the station is stable during the operating phases (flat surface andabsence of vibration).

• Ensure that the working area is correctly ventilated.

REMINDERDye must not be injected into the cold loop circuit using the chargingstation. Only use the specified equipment.

Connection of the charging station to the air-conditioning system

The charging station connection varies according to the number of refill valves.

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On this cold loop fitted with a singlevalve (figure 47), only the highpressure pipe of the station need beconnected.

Figure 47. Connection to a valve.

IMPORTANT

Whatever the charging station model, in the single-valve configuration(figure 47), all the operations (recovery, vacuum extraction, charging, etc.)are carried out using the high-pressure pipe of the charging station.

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Connection instructions

The instructions applicable to pipe connection are as follows:

• Verify the absence of pressure in the connection pipes.Pipes under pressure indicate that a quantity of refrigerant is present in thestation circuits. As this quantity is likely to distort the amount of refrigerantrecovered, it is essential to drain the pipes (valves closed) before making theconnection.

• Verify that the quick release connections are closed.The quick release connection (figure 48) must be in the closed position to beconnected to the charging valve. In the open position, it cannot be connectedand encourages the entry of airborne moisture into the pipe. Between eachuse, always keep the connection in the closed position.

Figure 48. Quick release connections.

• Connecting the quick release connections.Unlike the connections fitted to the R12 charging station, connection of theR134a quick release connections does not sytematically open the circuit. Con-nection and opening of the circuit are two separate operations.

• Opening the valves.Between the quick release connection and the charging station, each circuit(HP and LP) is closed by two valves: one fitted to the quick release connection,the other located on the station control panel. The essential function of thecontrol panel valve is to isolate the station circuit to allow a reading of the coldloop pressure.

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Recovery of the refrigerant

Figure 49. Recycling of the refrigerant.

IMPORTANT


Different recovery procedures

Whatever the condition of the engine and the air-conditioning system, the objectiveis to recover all the refrigerant present in the circuit before vacuum extraction oropening the circuit.

Three scenarios should be considered:

Scenario A. The engine and air-conditioning are operational.In this scenario, when the operating temperature is normal, the liquid is fully mixedand expanded. This is the ideal condition for carrying out a rapid and completerecovery of the refrigerant.

The time required for recovery will be the shortest.

Scenario B. The engine is operational but not the air-conditioning.In this scenario, the warm air blown against the evaporator (the coldest part of thecircuit) and the exchange of heat between the condenser and the engine radiatorassists expansion of the fluid and recovery of the refrigerant.

The exchange of heat at different places in the cold loop allows the fluid to expandand helps recovery.

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However, the time required for recovery is longer than in scenario A.

Scenario C. Neither the engine nor the air-conditioning system are opera-tional.In this scenario, the low pressure in the system makes recovery of the refrigerantvery slow.

In all the scenarios, it is necessary to perform several draining operations sep-arated by pauses (waiting time) in order to obtain a stabilised relative pressureequal to or less than 0 bar in the circuit.

The pauses vary according to the recovery procedure. Between each recoveryphase, they are 10 minutes (scenario A), 15 minutes (scenario B) and 2 hours(scenario C).

NOTEThis alternation of recoveries and pauses is essential to allow all the fluidto expand and gradually reach the output valve(s).

Verification and confirmation of the charge

The refrigerant charge present in the circuit must be verified each time a refrigerantrecovery is made.

This is the total of the amounts of draining operations which determines the totalquantity of refrigerant contained in the system.

The charge is correct if the quantity of refrigerant recovered is within the specifiedtolerance values.

If the quantity of refrigerant recovered is outside the tolerance values, proceed asfollows:

1. Ensure that the procedure used corresponds to the required conditions.

2. Ensure that all the stages of the recovery procedure have been performed.

3. If in doubt, repeat the procedure, adapted to the system conditions, taking careto note the quantity of refrigerant recovered previously.

4. When the quantity of refrigerant recovered is insufficient, a search for leaksmay be necessary.

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NOTEBefore carrying out a (partial) charge of refrigerant to locate a possibleleak, it is first necessary to carry out a sealing test of the circuit (undervacuum).

The recovered oil

During the recovery phase, the oil present in the refrigerant will be recovered bythe charging station, separated from the refrigerant and stored in the graduatedbottle provided for used oil (figure 50).

Figure 50. Measuring the recovered oil.

It is therefore essential to know the quantity of oil recovered to be able to inject anequal volume of new oil.

IMPORTANT

The oil extracted from the circuit cannot be reused and must be disposedof (or stored) using the procedure applicable to used oils. Refrigerant oil,however, must not be mixed with other used oils.

Refrigerant oil is hygroscopic and can easily be contaminated by the presence ofmoisture in the air. The contaminated oil then becomes acidic and attacks thecomponents of the air-conditioning circuit.

The oil can must always be closed after use to prevent contamination by moistureand oil in a can which has been open for a long time (viscous appearance) mustnever be used.

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Vacuum extraction

Figure 51. Vacuum extraction

Duration of vacuum extraction

The duration of the vacuum extraction depends on the time elapsed between drain-ing the refrigerant and the time when the vacuum extraction is performed.

Whenever the circuit is opened, the maximum recommended time must be takeninto account.

Purpose of vacuum extraction

The aims of vacuum extraction are as follows:

1. To remove any trace of moisture in the circuit.

2. Carry out a sealing test.

3. To assist the topping up of oil and transfer of refrigerant.

Vacuum extraction is an important stage which must not be cut short. The pres-ence (even slight) of moisture in the circuit may cause rapid deterioration of thecomponents.

NOTESubjecting the circuit to a vacuum lowers the boiling point of water, whichchanges from a liquid to a gas. This change of state helps to extract themoisture present in the circuit.

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Sealing test

The sealing test (under vacuum) verifies the performance of the circuit under vac-uum when it is only subject to ambient atmospheric pressure.

The sealing test under vacuum and the vacuum extraction are two associated op-erations.

With most charging stations, the two operations are automated. On these models,any sealing fault (poor vacuum performance over time) is indicated by an errormessage.

IMPORTANT

This test demonstrates the sealing of the circuit under vacuum, but doesnot guarantee sealing under pressure under normal operating conditions.

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Charging the circuit

Figure 52. Charging with refrigerant and oil.

Instructions applicable to charging operations

The instructions concern the following points:

The quantity of refrigerant to be transferredThe refrigerant capacity of vehicles depends on their engine and various specificcharacteristics.

IMPORTANT

It is essential to fill with the specified quantity. Failure to do this can affectperformance, even if a larger quantity than that specified is injected intothe system.

Topping up oilThe volume of new oil to be injected must be equal to the volume measured duringrecovery (figure 53).

When the refrigerant circuit is drained, it is never completely emptied: some oilremains in the various components of the system.

If a component is replaced, the quantity of oil recovered during the associateddraining operation must be replaced by topping up to the correct level.

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Figure 53. Topping up with new oil.

NOTEIt may be necessary to drain the compressor oil in the event of a rapid leak(broken component) or if the circuit is open for a long period.

There are different oils for the R134a refrigerant. Each oil is specific to the type ofcompressor and the use of another type of oil may cause serious damage to thecold loop.

In order to limit the risk of mixing oils, it is recommended that different top-up bottlesare provided on the charging station.

Confirming the chargeTo confirm the charge or any other operation requiring a conformity check, twooperations must be carried out:

1. Check that the system is operating correctly.The operational test consists of carrying out a performance test (See Verifica-tion of the efficiency of an air-conditioning system section).

2. Carry out a search for leaks.The search for leaks consists of performing a leak test with an electronic de-tector (See Leak test section).

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Conversion of an R12 air-conditioning circuit intoan R134a circuitConversion of the air-conditioning circuit

Following prohibition of R12 refrigerant production after 31 December 1995, vehi-cles whose air-conditioning circuits use R12 refrigerant (figure 51) must undergoconversion to R134a since R12 refrigerant is no longer available.

Figure 54. Conversion of a vehicle using R12 to R134a.

Conversion involves the following constraints:

• the operation is irreversible,

• the cost of conversion (R12 to R134a),

• unforeseen technical constraints resulting in additional cost.

REMINDERMaintenance operations on a cold loop require compliancewith the rulesfor environmental protection.

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Stages of the conversion procedure

It is essential to refer to the detailed conversion procedure in the technical docu-mentation.

1. Recover the R12 refrigerant fluid contained in the air-conditioning circuit of thevehicle using the special charging station, then extract under vacuum.

2. Disconnect the R12 charging station.

3. Replace the dehydration canister and the seals (the parts delivered are R12and R134a compatible).

4. Fit the adaptor and identification components to the charging valves on thevehicle and connect the charging station for R134a refrigerant.

5. Inject the recommended quantity of oil.

6. Carry out charging of the circuit.

7. Check that the system is operating correctly.

8. Around the pipes, as close as possible to the charging valves, attach a pro-tected information label (date of conversion, type and quantity of the new re-frigerant and oil, etc.).

Recovery of the oil

Recovery of the oil requires the greatest care in order to minimise the residualquantity of oil.

To improve oil recovery, it is necessary to follow the steps contained in the technicaldocumentation.

If it is not possible to follow the recommended method, it is essential to removethe compressor and drain its oil.

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Modification of the charging valves

As the charging valves in the R12 circuit are not compatible with the connectionsfor the R134a station, it is necessary to fit two adapters to the existing valves.

The conversion kit is available as a spare part.

Type of oil

During the conversion, only use the recommended type of oil.

Oil can be topped up using a charging station. If this is not possible, remove thecompressor in order to add oil to it.

After the R12/R134a conversion, if the compressor has to be replaced, it will benecessary to extract the oil contained in it and replace it with the oil recommendedfor the R134a refrigerant.

Identification label

Conversion of an R12 air-conditioning circuit into an R134a circuit is irreversible.The vehicle can no longer accept R12 refrigerant.

To avoid any risk of charging using R12 refrigerant, it is essential to place an in-formation and identification label as near as possible to the charging valves.

NOTEThe identification label is available as a spare part.

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Questionnaire

QUESTIONNAIRE1. What is the function of air-conditioning in a vehicle?

A To condense mist on the windows.

B To reduce the level of humidity in the passenger compartment.

C To Purify the air in the passenger compartment.

D To Recycle the air in the passenger compartment.

2. What is the condition of the refrigerant fluid when it leaves the compressor?

A Liquid and very hot.

B Gaseous and cold.

C Liquid and cold.

D Gaseous and very hot.

3. What is the function of the fixed orifice tube?

A To filter impurities contained in the fluid.

B To allow expansion of the fluid to produce cold.

C To reduce the volume of fluid in the circuit.

D To allow compression of the fluid to produce cold.

4. Where is the accumulator located on a fixed orifice tube circuit?

A Between the condenser and the evaporator, in the high-pressure section.

B At the condenser outlet.

C At the compressor outlet.

D Between the evaporator and the compressor, in the low-pressure section.

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Questionnaire

5. Which tool is used to validate an efficiency test?

A The tracer detector.

B The electronic detector.

C The digital multimeter.

D The digital thermometer.

6. Which control on the air-conditioning panel has no effect on the efficiency test?

A The rear screen demisting control.

B The fan speed control.

C The air distribution control.

D The recirculation control.

7. How can a clogged filter adversely affect the efficiency of the air-conditioningsystem?

A By causing excess pressure in the condenser.

B By reducing the volume and speed of the blown air.

C By increasing the temperature of the air drawn in.

D By preventing cycling of the compressor.

8. During a diagnostic procedure using the touchmethod, which component is hotat the inlet and cold at the outlet?

A The compressor.

B The evaporator.

C The expansion valve.

D The condenser.

9. What safety instructions must be followed when carrying out work on the cir-cuit?

A Work on a cold engine and in a well-ventilated area.

B Wear gloves and safety glasses.

C Disconnect the battery and lower the pressure in the circuit.

D Wear a mask, gloves and safety glasses.

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Questionnaire

10. According to the documentation, which method allows untraceable leaks to bedetected?

A Electronic detection.

B Vacuum performance at the end of vacuum extraction.

C Pressure performance when charging refrigerant.

D Detection by tracer.

11. Where must the electronic leakage detector be initialised?

A It is not necessary to initialise it.

B In the engine compartment.

C Near to the charging valve(s)

D In the glove compartment, if it is air-conditioned.

12. What is the first step when carrying out a service using a charging station?

A Recovery of the refrigerant and oil.

B Vacuum extraction.

C Measuring the recovered oil.

D The addition of 200 grams of refrigerant.

13. What is the main reason for vacuum extraction?

A To perform a circuit test under pressure.

B To assist the transfer of fluid during recovery.

C To extract a maximum of moisture and impurities from the circuit.

D To add oil to the circuit.

14. Why is it necessary to perform several drainage operations when recoveringrefrigerant?

A To avoid the emission of gas when opening the refrigerant circuit.

B To recover as much moisture as possible.

C To recover as many impurities as possible.

D To validate the sealing of the system.

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Questionnaire

15. During a servicing operation, what quantity of oil must be injected if no compo-nent needs replacing?

A It is not necessary to inject oil.

B The quantity of new oil to be injected must be identical to the quantity recovered.

C The quantity contained in the compressor.

D All the recovered oil must be reinjected.

16. How must the fluid contained in the circuit be drained?

A By venting the circuit to the open air.

B By using a special station.

C Via the compressor drain plug.

D Impossible, the circuit is sealed in the factory.

17. What is the special feature of the oil in the refrigerant circuit?

A The oil dissolves moisture.

B The oil solidifies at high temperature.

C The oil can be mixed with the other oils.

D The oil quickly absorbs moisture.

18. Why is the refrigerant fluid recovered using a charging station?

A To reduce the cost of servicing.

B To recover the refrigerant more quickly.

C To prevent gas emissions into the atmosphere.

D To assist the transfer of fluid during the filling process.

19. What operation must be carried out between the recovery and charging of thefluid?

A No operation is necessary.

B Pressurise the circuit.

C Check the dehydration reservoir filter.

D Perform vacuum extraction.

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Questionnaire

20. When converting the system from R12 to R134a, which components must bereplaced?

A The fluid, the oil, the compressor, the condenser.

B Only the fluid and the oil.

C The fluid, the oil, the dehydration canister, the seals, the valves.

D The whole circuit.

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Renault APV Training on AC Cold Loop

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Transcript of Renault APV Training on AC Cold Loop