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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.
Liquid
Diphasic
Gaseous
Refrigerant storage
(receiver drier)
Hp
Lp
Evaporator
Compressor
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).
Expansion
valve
Refrigerant storage
(receiver drier)
Hp
Lp
Evaporator
Compressor
°C
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.
Expansion valve -
closed
Expansion valve -
open
High
pressure fluid
High
pressure fluid
Evaporator
Evaporator
Expansion valve -
closed
High
pressure fluid
Evaporator
E
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