Impreza 2.5 RS Sedan AWD F4-2.5L SOHC (2002)
Expansion Valve: Description and Operation
COOLING UNIT
The heater unit and cooling unit are integrated into a single "heater and cooling unit".
The cooling section components of this unit include an evaporator, expansion valve, and case.
EXPANSION VALVE
The expansion valve regulates the flow of refrigerant such that heat exchange takes place optimally.
The expansion valve performs two functions; it sprays the high-pressure refrigerant from the condenser using a throttle valve, and it regulates the amount
of the spray by changing opening of the throttle valve.
The expansion valve consists of such main components as a heat sensing cylinder, diaphragm, ball valve, spring, and adjusting screw.
The heat (temperature) sensing cylinder is held in contact with the evaporator outlet pipe so that a pressure corresponding to the sensed temperature may
be applied to the chamber above the diaphragm. There is a pressure equalizing hole which communicates with the chamber below the diaphragm to
transmit changes in the refrigerant pressure to the chamber. The ball valve is linked with the diaphragm and moves according to changes in the balance
between the force applied to the diaphragm and the tension of the spring.
