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2.3.9 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 liquid. A portion of the condenser coil is occupied by the subcooler,
which removes heat from the refrigerant liquid leaving the receiver. Air movement over the condenser, subcooler
and radiator is provided by the condenser fans.
2.3.10 Economizer Circuit
The economizer circuit consists of a compact brazed plate heat exchanger (Figure 2.1) and the economizer
expansion valve (ECXV). Both are located above the compressor.
In the economized mode, the frozen and pull down capacity of the unit is increased by subcooling the liquid
refrigerant entering the evaporator expansion valve. Overall efficiency is increased because the gas leaving the
economizer enters the compressor at a higher pressure, therefore requiring less energy to compress it to the
required condensing conditions.
To place the unit in the economized mode, the control system energizes (opens) the ECXV. The ECXV controls the
flow of liquid from the main liquid line through the economizer according to changes in superheat of the refrigerant
leaving the economizer.
2.3.11 Economizer Transducer and Sensor
2.3.11.1 Economizer Outlet Pressure Transducer (ECOP)
The ECOP is located in the vapor injection line leaving the economizer. It provides the control system with
economizer outlet pressure information to be displayed, recorded in the data recorder, and used to deter-
mine the required position of the economizer expansion valve.
2.3.11.2 Economizer Outlet Temperature Sensor (ECOT)
The ECOT is a thermistor type sensor located on the suction line leaving the economizer. It provides the
control system with economizer outlet temperature information to be displayed, recorded in the data
recorder and used to determine the required position of the economizer expansion valve.
2.3.12 Ambient Air Temperature Sensor (AAT)
The AAT is a thermistor type sensor that provides the control system with the temperature of the air entering the
condenser. This temperature information is displayed, recorded in the data recorder and used to control the refrig-
eration system. The sensor is located behind the front grill.
2.3.13 Compressor Suction Modulation Valve (CSMV)
The CSMV opens and closes as required for capacity control of the refrigeration system cooling cycle. It is located
in the suction line just above the compressor.
2.3.14 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 moisture from the refrigerant.
2.3.15 Receiver
Liquid refrigerant from the condenser flows into the receiver. 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 bulls-eye sight
glasses, for the observation of liquid level and moisture content, and a fusible plug.
2.3.16 AutoFresh Air Exchange
As perishable products respire, they consume oxygen (O
2
) and give off carbon dioxide (CO
2
). This will eventually
cause the atmosphere in a refrigerated compartment to have higher levels of CO
2
and lower levels of O
2
. This may
adversely affect shelf life of some sensitive perishable products. When transporting these products, it may be desir-
able to maintain normal atmospheric conditions (prevent build up of CO
2
and depletion of O
2
) by using fresh air
exchange, in addition to accurate temperature control. AutoFresh Air Exchange (Figure 2.2) controls the amount of
fresh air entering the refrigerated compartment without manual intervention while in transit. AutoFresh Air Exchange
can also be used to lower humidity level in a refrigerated compartment if ambient air has a lower humidity level.
AutoFresh Air Exchange is a factory-installed option, as it requires a modified evaporator pod. When air is being
exchanged, two air ports open. The upper port allows fresh ambient air to enter while stale air exits through the
lower port.
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