Case 580SR, Service Manual

Page: 784 / 1068

24 SECTION 50 - CAB HEATING AND AIR CONDITIONING
When the system is started, the pressure on the bot-
tom of the diaphragm lowers rapidly, allowing the or-
ifice to open and metre atomized liquid refrigerant to
the evaporator where it begins to vaporize.
Suction from the compressor draws the vaporized
refrigerant out of the evaporator and back through a
gallery in the top of the valve which asses the tem-
perature sensor.
The temperature sensor reacts to variations in refrig-
erant gas pressure returning from the evaporator.
When heat from the passenger compartment is ab-
sorbed by the refrigerant the pressure of the gas in-
creases causing a differential pressure above and
below the temperature sensor diaphragm. The dia-
phragm reacts to this pressure differential and a
push rod forces the ball in the expansion valve orifice
further off its seat. This reaction allows an increase
in the atomized refrigerant to flow through the valve,
to the evaporator, so that more heat can be absorbed
by the air conditioning system.
Similarly when the temperature of the gas returning
from the evaporator decreases the pressure of the
gas decreases. This causes the diaphragm to react
accordingly and allow the ball in the orifice to move
closer towards its seat thus reducing the flow of re-
frigerant through the valve to the evaporator.
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