moisture-sensitive element built into the sight glass. If
pressure exerted on the diaphragm from the thermal
excessive moisture is present, the element turns pink. If
bulb. Operation of the valve is as follows.
the system moisture content is within limits, the element
(1) High-pressure liquid refrigerant flows into the
valve and is stopped at the needle seat.
(2) If the evaporator is warm, pressure is
37-5. Refrigerant Expansion Systems. The
developed in the thermal bulb and transferred to the
refrigerant expansion systems are designed to regulate
diaphragm through the capillary tube.
the amount of refrigerant entering the evaporator and
also reduce its pressure.
(3) The diaphragm overcomes the pressure
developed in the equalizer tube and valve spring
pressure, causing it to move downward.
a. Expansion Valve. One type of expansion
system used on modern vehicles is the expansion valve
(4) This movement forces the valve actuating
(A, fig. 37-4). The valve action is controlled by the valve
pin downward to open the valve.
spring, suction manifold, and
Figure 37-4. Expansion Valve and Expansion Tube.