Figure 13-5.Expansion valve and expansion tube.
3. The diaphragm overcomes the pressure
One type of expansion system used on modem
vehicles is the expansion valve (view A, fig. 13-5). The
valve action is controlled by the valve spring, suction
manifold, and pressure exerted on the diaphragm from
the thermal bulb. Operation of the valve is as follows:
1. High-pressure liquid refrigerant flows into the
valve and is stopped at the needle seat.
2. If the evaporator is warm, pressure is developed
in the thermal bulb and transferred to the diaphragm
through the capillary tube.
developed in the equalizer tube and valve spring
pressure, causing it to move downward.
4. This movement forces the valve-actuating pin
downward to open the valve.
As the refrigerant flows, it cools the evaporator and
therefore reduces pressure in the thermal bulb. This
allows the valve to close and stop refrigerant from
flowing into the evaporator. By carefully metering the
amount of refrigerant with the expansion valve, the
evaporator cooling efficiency is increased greatly.