Air Conditioning Fundamentals
TC070-05-01S
5 – AIR CONDITIONING
COMPONENTS
34
EXPANSION VALVE / ORIFICE TUBE
An expansion valve or orifice tube regulates the flow of refrigerant to the
evaporator. To get maximum cooling potential, the pressure of the liquid
refrigerant must be lowered before it enters the evaporator. At lower
pressure, the refrigerant’s temperature and boiling point drop, allowing it
to absorb more heat as it passes through the evaporator.
Expansion Valve
Although they perform the same function, expansion valves and orifice
tubes operate differently. Figure 17 shows a typical expansion valve.
A bulb on the evaporator sends information about evaporator
temperature through a capillary tube . This tube is attached to the
diaphragm on the expansion valve.
If the evaporator becomes too cold, the diaphragm pulls the
needle-shaped pintle , closing the valve and restricting refrigerant
flow. As the evaporator temperature rises, the diaphragm presses down
on the pintle, opening the valve and letting more refrigerant through.
FIGURE 17. The
expansion valve
restricts the flow
of refrigerant to
the evaporator.
Lowering the
pressure of the
refrigerant allows
it to absorb more
heat as it passes
through the
evaporator.
Diaphragm
Capillary tube
Temperature-
sensing bulb
Valve
Pintle
Pressure
spring