Valeooscope - Air Conditioning System Thermal comfort loop

11.5.1 Simplified description

Operation: The expansion valve reduces the pressure of the refrigerant fluid upstream of the evaporator. This drop in pressure produces cold. It also transforms the fluid from the liquid to the diphasic state. The diphasic fluid is then sprayed into the evaporator. The expansion valve is always attached to the eva- porator.

Based on the temperature information, the expansion valve adjusts the volume of fluid injected into the eva- porator, therefore, according to the thermal require- ments of the system (thermal load of the evaporator). The expansion valve is designed specifically for each new application of the A/C loop. The expansion valve is a precision component that is complex and sensitive to the residue and acid flowing through the air conditioning loop. A blocked expansion valve can result in either a signi- ficant loss of cold or the destruction of the compressor (frozen evaporator). Regular system maintenance is essential to guarantee the longevity of the expansion valve, therefore, it is essential to replace the receiver drie r. Refrigerant flow in the expansion valve In hot summer weather, the expansion valve lets more fluid enter the evaporator in order to produce a greater heat exchange. The expansion valve permanently checks that the change in the state of the fluid in the evaporator occurs properly.

Liquid

Diphasic

Gaseous

Hp

Lp

Compressor

Evaporator

Refrigerant storage (receiver drier)

11.5.2 Real description

The expansion valve is a regulation device. It is controlled according to the temperature of the refri- gerant at the evaporator outlet. The expansion valve measures the temperature of the fluid at the evaporator outlet. This temperature is determined by the heat exchanges taking place inside the evaporator and varies according to the conditions inside and outside the cold loop (volume of fluid, temperature, pressure).

High pressure fluid

E

Evaporator

Expansion valve - closed

Expansion valve

Hp

Lp

High pressure fluid

Evaporator

High pressure fluid

Evaporator

Evaporator

Compressor

Expansion valve - closed

Expansion valve - open

°C

Refrigerant storage (receiver drier)

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