Fundamentals of refrigerant circuits TT-011-0808 Fundamentals of refrigerant circuits

Contents Refrigerant circuit with expansion valve Refrigerant circuit with restrictor Refrigerant circuit with second evaporator Components in refrigerant circuit 08.2008 • VSQ/TT • 2/14

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 08.2008 • VSQ/TT • 3/14

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 08.2008 • VSQ/TT • 4/14

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. 08.2008 • VSQ/TT • 5/14

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 08.2008 • VSQ/TT • 6/14

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 08.2008 • VSQ/TT • 7/14

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 08.2008 • VSQ/TT • 8/14

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 08.2008 • VSQ/TT • 9/14

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 08.2008 • VSQ/TT • 10/14

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 08.2008 • VSQ/TT • 11/14

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 08.2008 • VSQ/TT • 12/14

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. 3.0 - 3.5 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 08.2008 • VSQ/TT • 13/14

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. 08.2008 • VSQ/TT • 14/14

Thank you 08.2008 • VSQ/TT • 15/14

Break 08.2008 • VSQ/TT • 16/14