Refrigerant flow to the evaporator must be
controlled to obtain maximum cooling,
while ensuring that complete evaporation
of the liquid refrigerant takes place. This is
accomplished by the thermal expansion
valve (TXV).
Pressures in control
As shown in the illustration, the TXV
controls the refrigerant flow by using a
system of opposing pressures which will
call:
F1 - Temperature sensing capillary tube
Sealed tube filled with refrigerant. This
refrigerant is also filled above the
diaphragm (7). The capillary tube sensing
bulb (3) is attached to the evaporator
outlet tube surface.
F2 - Pressure compensation tube
This is a hollow tube connected to the
evaporator outlet tube and senses the
pressure of the R134a refrigerant leaving
the evaporator coil. (Other TX valves may
not use this tube as pressure is provided
internally within the valve).
F3 - Pressure spring
This spring (6) is located under the ball
valve (5).