1. Fundamentals of refrigerant circuitsTT
Fundamentals of refrigerant circuits

2. Contents Refrigerant circuit with expansion valve
Refrigerant circuit with restrictor
Refrigerant circuit with second evaporator
Components in refrigerant circuit
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3. Refrigerant circuit with expansion valve
System overview
A – Compressor
B – Condenser
C – Receiver with dryer
D – Pressure switch
E – Extraction and charge valve, high pressure
F – Expansion valve
G – Evaporator
H – Extraction and charge valve, low pressure
I – Pressure and vibration damper
F208_004
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4. Refrigerant circuit with restrictor
System overview
A – Compressor
B – Pressure switch, high pressure
C – Condenser
D – Extraction and charge valve, high pressure
E – Restrictor
F – Evaporator
G – Pressure switch, low pressure
H – Extraction and charge valve, low pressure
I – Reservoir with dryer
F208_007
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5. Refrigerant circuit with second evaporator
System overview D C B A
A – Refrigerant temperature sensor
B – Temperature sensor after evaporator
C – Evaporator in rear
D – Expansion valve II
The remaining components are the same.
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6. Components in refrigerant circuit
Condenser
Condenser
Radiator
Radiator fan
The condenser shown here is a so-called round pipe condenser. More frequently, so-called parallel flow condensers are used in today's vehicles. This new construction feature optimises the degree of efficiency of the condenser.
The radiator need not have a direct connection to the condenser! Look for contamination between components and clean if necessary.
In the event problems, check the direction of rotation of the radiator fan/s.
F208_024
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7. Components in refrigerant circuit
Receiver with dryer
To expansion valve
Dryer
This receiver with dryer is used in the refrigerant circuit with an expansion valve.
This component serves as a reservoir tank for the expansion valve.
Depending on its type, the dryer can only chemically bind a certain amount of water!
With new vehicle models, a dryer is coupled directly to the condenser as a replaceable cartridge.
When replacing/changing, always follow the instructions in the current workshop manual!
F208_025
From condenser
Filter strainer
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8. Components in refrigerant circuit
Reservoir with dryer
Plastic cap
Suction point for gaseous refrigerant
To compressor
From evaporator
Dryer
This reservoir with dryer is used in the refrigerant circuit with restrictor.
This reservoir has an extra large volume so that refrigerant which has only evaporated in part can evaporate here completely. This component is also often referred to as an after-evaporator.
The U-pipe in the reservoir prevents the compressor from drawing in fluid refrigerant. The plastic cap prevents refrigerant from reaching the suction point in unvaporised state (!!!).
When replacing/changing, always follow the instructions in the current workshop manual!
U-pipe
Filter strainer
Hole for refrigerant oil
F208_037
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9. Components in refrigerant circuit
Expansion valve with external diaphragm unit
Thermostat with sensor lead
Diaphragm
To compressor
Out of evaporator (low pressure)
Into evaporator (low pressure)
From condenser (high pressure)
The characteristic of the expansion valve is matched to the evaporator. The characteristic is determined by the type of gas in the sensor line and by the screw adjustment on the regulating spring.
The diaphragm unit must be insulated if located in hot spots!
Ball valve
F208_015
Regulating spring
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10. Components in refrigerant circuit
Expansion valve with internal diaphragm unit
To compressor (low pressure)
Out of evaporator (low pressure)
Diaphragm
Thermal head with special gas filling
Plunger rod
Pressure compensation holes
Into evaporator (low pressure)
From condenser (high pressure)
If heat insulation is missing from the valve, a change in the selected control characteristic will be the result!
Video "Expansion valve"
F208_017
Regulating spring
Ball valve
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11. Components in refrigerant circuit
Restrictor
To evaporator
Strainer for atomisation
Calibrated drilling
F208_016
Dirt strainer
O-ring, seals high pressure side against low pressure side.
Caution! Note installation position. Arrow on restrictor points to evaporator
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12. Components in refrigerant circuit
Evaporator
Refrigerant return (gaseous)
Refrigerant supply (gaseous)
Round pipe evaporator
Function:
The refrigerant released by the expansion valve or restrictor expands in the evaporator, which thereby cools down rapidly. From droplet state, it is then changed to vapourous state.
At boiling point in the evaporator, the temperatures are way below the freezing point of water. The heat required for evaporation is drawn in by the refrigerant from the surrounding air – in this case, the air flowing through the evaporator. This air is channelled as cooling air into the passenger compartment.
The humidity of the cooled air is dispersed in the evaporator at the points where it is below the dew point temperature, i.e. it condenses. The result is condensation. The air is "dried". Suspended matter present in the air is dispersed in the evaporator. The evaporator thus also "cleans" the air.
F208_030
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13. Components in refrigerant circuit
Evaporator
Pressure relief valve
The valve (previously dump valve) is attached directly to the compressor or the receiver.
It opens at approx. 3.8 MPa (38 bar) and closes when pressure has been released (approx MPa).
Depending on the type installed, there may be a plastic washer that breaks out as soon as the valve responds. In this case, the cause of overpressure in the system must be determined.
Renew dump valve only when the refrigerant circuit is empty!
F208_056
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14. Components in refrigerant circuit
Extraction and charge valves
Caution! Always use O-rings with sealing caps.
Car valve insert installed. Use matching tool T10364 to loosen and tighten.
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15. Thank you
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16. Break
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