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d. Compressor Suction Temperature Sensor (CST)
The CST provides a signal to the microprocessor
equivalent to to the temperature of the gas entering the
compressor suction service valve. It is located on the
line entering the valve.
e. High Pressure Switch (HP1)
The HP1 is normally closed and opens on pressure rise
to signal to the microprocessor to shutdown the engine,
or shutdown the system if operating on standby power. It
is located on the compressor center head.
2.3.8 Condenser Coil
The condenser coil is a microchannel type and acts as a
heat exchanger in which the compressed refrigerant
gas is lowered in temperature and condensed into a li-
quid. Air movement over the condenser is provided by
two electric motor driven fans mounted in the condens-
ing section.
2.3.9 Ambient Air Temperature Sensor (AAT)
The AAT provides microprocessor with condenser
entering air temperature information to be displayed,
recorded in the DataLink data recorder and used to
control the refrigeration system. The sensor is located
behind the front grill.
2.3.10 Filter-Drier
The filter-drier is a cylindrical shell containing a drying
agent and filter screen. It is installed in the liquid line and
functions to keep the system clean and remove mois-
ture from the refrigerant.
2.3.11 Receiver
Liquid refrigerant from the condenser flows into the re-
ceiver. The receiver serves as a liquid reservoir when
there are surges due to load changes in the system; as a
storage space when pumping down the system and as a
liquid seal against the entrance of refrigerant gas into
the liquid line.
The receiver is provided with two bull's-eye sight
glasses, for the observation of liquid level & moisture
content, and a fusible plug.
2.4 EVAPORATOR SECTION
The evaporator (See Figure 2−4) fits into a rectangular
opening in the upper portion of the front wall of the refri-
gerated compartment. When installed, the evaporator
section is located inside the compartment, and the con-
densing section is outside.
The evaporator assembly consists of an evaporator coil,
evaporator fan motor, electronic expansion valve, coil
heaters, heat exchanger, defrost termination temperat-
ure sensor the supply and return air sensors and a high
temperature switch.
Heating and defrost is accomplished by electric heaters
mounted on the coil.
Automatic evaporator coil defrosting is initiated by either
a differential air switch (which senses the pressure drop
across the coil) or by the defrost timer in the micropro-
cessor.
62-11389
2.4.1 Evaporator Coil
The evaporator is a tube in fin type. The operation of the
compressor maintains a reduced pressure within the
coil. At this reduced pressure, the liquid refrigerant
evaporates at a temperature sufficiently low enough to
absorb heat from the air. The electric heaters (HTR1 &
HTR2) are mounted on the inlet side of the coil.
2.4.2 Electronic Expansion Valve (EVXV)
The EVXV is an electronic device which controls the
flow of liquid to the evaporator according to changes in
superheat of the refrigerant leaving the evaporator. The
expansion valve maintains a relatively constant degree
of superheat in the gas leaving the evaporator regard-
less of suction pressure. The valve has a dual function -
automatic expansion control and prevention of liquid
return to the compressor.
2.4.3 Heat Exchanger
The heat exchanger is the tube in tube type and is in-
stalled in the main suction line and liquid line. The suc-
tion gas is used to cool the warm liquid refrigerant within
the heat exchanger. This results in greater system effi-
ciency.
2.4.4 Compressor
(CSMV)
The CSMV opens and closes as required for capacity
control of the refrigeration system cooling cycle. It is
located in the suction line at the exit of the evaporator
assembly.
2.4.5 Evaporator Switches, Transducers and Sen-
sors
a. Evaporator Outlet Pressure Transducer (EVOP)
The
EVOP
provides
evaporator outlet pressure information to be displayed,
recorded in the DataLink data recorder and used to
control the refrigeration system. It is located in the
suction line near the electronic expansion valve.
b. Evaporator High Temperature Switch (1EVHTS)
1EVHTS is a safety switch which opens on a temperat-
ure rise to de-energize the electric heaters if the temper-
ature reaches the cut-out point. It is located on the road-
side tube sheet of the evaporator coil
c. Evaporator Outlet Temperature Sensor (EVOT)
The
EVOT
provides
evaporator outlet temperature information to be
displayed, recorded in the DataLink data recorder and
used to control the refrigeration system. It is located on
the suction line near the electronic expansion valve.
d. Defrost Termination Temperature Sensor (1DTT)
The 1DTT is located on the curbside tube sheet of the
evaporator coil. It provides the microprocessor with
evaporator temperature information to be displayed, re-
corded in the DataLink data recorder and used to de-
termine termination of defrost.
e. Return Air Temperature Sensor (1RAT)
The 1RAT is a temperature control probe which pro-
vides the microprocessor with information on the tem-
perature of the air entering the evaporator section. The
2−10
Suction
Modulation
the
microprocessor
the
microprocessor
Valve
with
with
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