7
3.3.3 - The evaporator pump
In appropriate cases the controller can also regulate an evapo-
rator pump. This facility does not require an additional board.
3.3.4 - The condenser pump
In appropriate cases the controller can also regulate a condenser
pump (for water-cooled units). This control does not require an
additional board.
3.3.5 - The evaporator heater
The evaporator heater can be regulated by the unit control on
air-cooled units to protect the evaporator against frost. This
control requires an additional board.
3.3.6 - Pressure sensors
These are used to measure the following pressures in each
circuit:
• Discharge gas pressure (high pressure type)
• Suction pressure (low pressure type)
• Oil pressure (high pressure type, except for the low
ambient temperature option when the sensor used is a
wide-band sensor)
• Economizer pressure (high pressure type)
These electronic sensors deliver 0 to 5 V d.c. The economizer
and oil pressure sensors are connected to the SCPM board and,
as the others, are measured by the basic board.
Discharge pressure sensors
These are on the high pressure side of each circuit. They
replace the usual discharge gas pressure gauges and are used to
control head pressure or high pressure load shedding.
Oil pressure sensors
These sensors are located at the oil pressure port of each
compressor. The economizer pressure is subtracted from this
value to arrive at the differential oil pressure.
Suction pressure sensors
They are located in the high-pressure side of the evaporator,
and measure the low-pressure side of each circuit.
Economizer pressure sensors
These sensors measure the intermediate pressure between high
and low pressure. They are used to control the oil pressure
differential. They are located at the plate heat exchanger outlet
(for units equipped with economizers) or on the motor cooling
line of each motor.
3.3.7 - Thermistors
These all have similar characteristics.
Evaporator entering and leaving water temperature sensor
The evaporator entering water temperature sensor and the
leaving water temperature sensor are installed in the entering
and leaving side water box.
Discharge gas sensor
This sensor is used to measure the discharge gas temperature,
and permits control of the discharge temperature superheat. It
is located in the discharge line of each compressor.
Motor sensor
This is used to control the motor temperature of each compressor.
The terminals of this sensor are situated on the compressor
terminal board.
Condenser entering and leaving water temperature sensors
These are used to control the heating capacity on heat pumps.
In cooling only units they have no control function. They are
installed in the common condenser entering and leaving line.
Heat reclaim condenser entering/leaving water temperatures
These sensors measure the entering and leaving water tempera-
tures of heat reclaim condensers and are used on air-cooled
units. They may be fitted as options.
Temperature setpoint reset sensor
This is an optional 0-10 V sensor which can be installed
remotely from the unit. It is used to reset the cooling and
heating setpoint on the unit as a function of either the outdoor
air temperature or ambient room temperature. The sensor is not
supplied by Carrier, and must be configured in the User Menu.
Outdoor temperature sensor
Mounted on the control box. It is used for start-up, setpoint
temperature reset and frost protection control.
Master/slave assembly temperature control
The optional water temperature sensor can be used for
master/slave assembly control.
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