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SiUS121827E Control Specification
Part 4 Functions and Control 103
Note(s)
In case of low outdoor temperature operation, the system compares the indoor heat exchanger
temperature with the liquid pipe temperature to detect disturbances in the refrigerant flow. If
any, the system adjusts the opening of the electronic expansion valve to control the refrigerant
flow.
When only one indoor unit is in heating operation, the liquid pipe thermistor is used for
subcooling control. The actual subcool is calculated with the liquid pipe temperature and the
maximum indoor heat exchanger temperature. The system controls the electronic expansion
valve openings to obtain the target subcool.
In heating operation, the liquid pipe thermistor is used for liquid pipe isothermal control. The
system controls the electronic expansion valve opening so that the liquid pipe temperatures in
each room becomes equal.
(6) Indoor Heat
Exchanger
Thermistor
The indoor heat exchanger thermistor is used for controlling the target discharge pipe
temperature. The system sets the target discharge pipe temperature according to the outdoor
and indoor heat exchanger temperature, and controls the electronic expansion valve opening so
that the target discharge pipe temperature can be obtained.
In cooling operation, the indoor heat exchanger thermistor is used for freeze-up protection
control. If the indoor heat exchanger temperature drops abnormally, the operating frequency
becomes lower or the operation halts.
In cooling operation, the indoor heat exchanger thermistor is used for anti-icing function. If any
of the following conditions are met in the room where operation halts, it is assumed as icing.
The conditions are
Tc ≤ – 1°C (30.2°F)
Ta – Tc ≥ 10°C (18°F)
where Ta is the room temperature and Tc is the indoor heat exchanger temperature.
The indoor heat exchanger thermistor is used for wiring error check function. The refrigerant
flows in order from the port A to detect the indoor heat exchanger temperature one by one, and
then wiring and piping can be checked.
In heating operation, the indoor heat exchanger thermistor is used for heating peak-cut control.
If the indoor heat exchanger temperature rises abnormally, the operating frequency becomes
lower or the operation halts.
In heating operation, the indoor heat exchanger thermistor is used for detecting the
disconnection of the discharge pipe thermistor. When the discharge pipe temperature drops
below the highest indoor heat exchanger temperature by more than a certain value, the
discharge pipe thermistor is judged as disconnected.
Excluding the case that all the indoor units are in heating operation, the indoor heat exchanger
thermistor is used for subcooling control. The actual subcool is calculated with the liquid pipe
temperature and the indoor heat exchanger temperature. The system controls the electronic
expansion valve openings to obtain the target subcool.
(7) Room
Temperature
Thermistor
The room temperature thermistor detects the room air temperature and is used for controlling
the room air temperature.
The refrigerant circuit has a fusible plug.
In order to prevent the increase of pressure when abnormal heating is caused by fire or others, the
fusible part of the plug is molten at a temperature of 70 - 75°C (158 - 167°F) to release the pressure
into the atmosphere.
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