Carrier TRANSICOLD Vector 8500, Operation & Service Manual

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2.3.6 Compressor Switches, Transducers and
Sensors
a. Compressor Discharge Pressure Transducer
(CDP)
The CDP provides a signal to the control system equiv-
alent to pressure leaving the compressor. The reading
is displayed, recorded in the DataLink data recorder
and used to control the refrigeration system. It is
located in the discharge line leaving the compressor.
b. Compressor Suction Pressure Transducer
(CSP)
The CSP provides a signal to the control system equiv-
alent to pressure entering the compressor. The reading
is displayed, recorded in the DataLink data recorder
and used to control the refrigeration system. It is
located in the suction service valve.
c. High Pressure Switch (HPS)
The HPS is normally closed and opens on pressure
rise to signal the control system to shutdown the refrig-
eration system if the discharge pressure rises above
the switch setting. It is located in the discharge service
valve.
d. Compressor Discharge Temperature Sensor
(CDT)
The CDT is a thermistor type sensor that provides a
signal to the control system equivalent to the tempera-
ture of the gas leaving the compressor. The reading is
displayed, recorded in the DataLink data recorder and
used to control the refrigeration system. It is located on
the compressor head.
e. Compressor Suction Temperature Sensor (CST)
The CST is a thermistor type sensor that provides a
signal to the control system equivalent to the tempera-
ture of the gas entering the compressor suction service
valve. The reading is displayed, recorded in the Data-
Link data recorder and used to control the refrigeration
system. It is located on the line entering the service
valve.
2.3.7 Liquid Injection Solenoid Valve (LIV)
The LIV is opened during periods of high compressor
discharge temperature to inject refrigerant into the
economizer connection to cool the compressor. It is
located at the front of the economizer.
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
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 con-
denser, subcooler & radiator is provided by the con-
denser fans.
2.3.9 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 liq-
uid 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 con-
trols the flow of liquid from the main liquid line through
the economizer according to changes in superheat of
the refrigerant leaving the economizer.
2.3.10 Economizer Transducer and Sensor
a. 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 dis-
played, recorded in DataLink data, and used to deter-
mine the required position of the economizer
expansion valve.
b. 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 DataLink
data recorder and used to determine the required posi-
tion of the economizer expansion valve.
2.3.11 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 dis-
played, recorded in the DataLink data recorder and
used to control the refrigeration system. The sensor is
located behind the front grill.
2.3.12 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.
2.3.13 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.