![background image](http://html1.mh-extra.com/html/carrier/30xav/30xav_control-manual_2564187007.webp)
7
Liquid pressure sensors (high pressure type)
These sensors measure the liquid pressure after the coils in
each circuit.They are used for EXV control.
Water pressure sensors (low pressure type)
These sensors measure the water pressure before the pump
and after the evaporator. Only units fitted with the optional
hydronic kit have these sensors included.
3.6 - Temperature sensors
Temperature sensors constantly measure the temperature
of various components of the unit, ensuring the correct
operation of the system.
Evaporator entering and leaving water temperature sensors
The evaporator entering and leaving water temperature
sensors are installed in the entering and leaving side water
box. They are used for capacity control and safety purposes.
Outdoor air temperature sensor
This sensor is mounted on the control box of air-cooled
units. Outdoor temperature sensor is used for start-up,
setpoint temperature reset and freeze protection control.
Suction gas temperature sensor
This sensor is used to control the suction gas temperature.
It is located at the suction side of each compressor.
Discharge gas temperature sensor
This sensor is used to control the discharge gas temperature,
and permits control of the discharge superheat temperature.
It is located at the discharge side of each compressor.
Liquid line temperature sensors
These sensors are used to control the liquid line
temperature in each circuit. They are used for EXV
control to maintain the subcooling setpoint.
Economizer gas temperature sensors
These sensors measure the economizer line temperature
in each circuit.
Compressor motor temperature sensors
These sensors are used to control the motor temperature
of each compressor.
Temperature setpoint reset sensor (optional)
This sensor measures the space (room) temperature for
the purpose of setpoint reset. Only units with the optional
energy management module are fitted with this sensor.
Master/slave common fluid temperature sensor (optional)
This sensor is used to control the operation of chillers in
the master/slave assembly. This sensor is located on the
common chilled leaving piping. Only units in the master/
slave configuration are fitted with this sensor.
3.7 - Actuators
Evaporator pumps
The controller can regulate one or two evaporator pumps
and takes care of the automatic changeover between these
pumps (see also section 6.3).
Electronic expansion valve
The electronic expansion valve (EXV) is used to adjust the
refrigerant flow to changes in the operating conditions of
the machine. To adjust the refrigerant flow, a piston moves
constantly up or down to vary the cross-section of the
refrigerant path. This piston is driven by an electronically
controlled linear stepper motor. The high degree of
accuracy with which the piston is positioned provides
precise control of the refrigerant flow.
Water flow switch
For units without internal pumps, the water flow switch
configuration allows for the automatic control of the
minimum water flow setpoint of the water flow switch.
The configuration depends on the unit size and is made
automatically at the start-up. If the measured water flow
rate in the water loop is lower than the configured flow
rate, the alarm condition shuts off the unit.