62-12259 2–10
2.4 Evaporator Section
The evaporator (Figure 2.3) fits into a rectangular opening in the upper portion of the front wall of the refrigerated
compartment. When the unit is 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, evaporator expansion valve, evaporator
outlet pressure transducer, evaporator outlet temperature sensor, defrost termination temperature sensor, supply
temperature sensor and return air temperature sensor.
Heating and defrost is accomplished by electric heaters mounted on the coil.
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. Air movement over the coil is provided by the evaporator fan and motor (EVM) assembly.
The electric heaters (HTR1 and HTR2) are mounted on the inlet side of the coil and in the drain pan. Automatic
evaporator coil defrosting is initiated by either a defrost air switch (DAS - which senses the pressure drop across
the coil) or by the control system defrost timer. During defrost the refrigeration system is shut down and the evapo-
rator fan and heaters operated as required by the defrost mode.
2.4.2 Evaporator Expansion Valve (EVXV)
The EVXV is an automatic device which controls the flow of liquid to the evaporator according to changes in super-
heat of the refrigerant leaving the evaporator. The expansion valve maintains a relatively constant degree of super-
heat in the gas leaving the evaporator regardless of suction pressure. The valve has a dual function - automatic
expansion control and prevention of liquid return to the compressor.
2.4.3 Evaporator Switches, Transducers and Sensors
2.4.3.1 Evaporator Outlet Pressure Transducer (EVOP)
The EVOP is located in the suction line near the evaporator expansion valve. It provides the control system
with evaporator outlet pressure information to be displayed, recorded in the data recorder and used to
determine the required position of the evaporator expansion valve.
2.4.3.2 Evaporator Outlet Temperature Sensor (EVOT)
The EVOT is a thermistor type sensor located on the suction line near the evaporator expansion valve. It
provides the control system with evaporator outlet temperature information to be displayed, recorded in the
data recorder and used to determine the required position of the evaporator expansion valve.
2.4.3.3 Evaporator High Temperature Switch (EVHTS)
EVHTS is a safety switch which opens on a temperature rise to de-energize the electric heaters if the tem-
perature reaches the cutout point. It is located on the curbside tube sheet of the evaporator coil.
2.4.3.4 Defrost Termination Temperature Sensor (1DTT)
The defrost termination temperature sensor is located on the roadside tube sheet of the evaporator coil. It
provides the control system with evaporator temperature information to be displayed, recorded in the data
recorder and used to determine termination of defrost.
2.4.3.5 Return Air Temperature Sensor (1RAT / RAT2)
1RAT and RAT2 (if equipped) are thermistor type temperature control probe which provides the control
system with information on the temperature of the air entering the evaporator section. The reading is dis-
played, recorded in the data recorder and used to control the refrigeration system. It is located on a bracket
behind the center of the return air grille.
2.4.3.6 Supply Air Temperature Sensor (1SAT)
The 1SAT is a thermistor type temperature control probe which provides the control system with informa-
tion on the temperature of the air leaving the evaporator section. The reading is displayed, recorded in the
data recorder and used to control the refrigeration system. It is located in the supply air outlet housing.
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