SiUS12-928_B
Function of Thermistor
Function and Control
52
(1) Outdoor Heat
Exchanger
Thermistor
1. The outdoor 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 outdoor electronic expansion valve
opening so that the target discharge pipe temperature can be obtained.
2. In cooling operation, the outdoor heat exchanger thermistor is used for detecting the
disconnection of the discharge pipe thermistor. When the discharge pipe temperature becomes
lower than the outdoor heat exchanger temperature, the discharge pipe thermistor is judged as
disconnected.
3. In cooling operation, the outdoor heat exchanger thermistor is used for high pressure protection.
(2) Discharge
Pipe Thermistor
1. The discharge pipe thermistor is used for controlling discharge pipe temperature. If the
discharge pipe temperature (used in place of the inner temperature of the compressor) rises
abnormally, the operating frequency becomes lower or the operation halts.
2. The discharge pipe thermistor is used for detecting disconnection of the discharge pipe
thermistor.
(3) Gas Pipe
Thermistor
1. In cooling operation, the gas pipe thermistor is used for gas pipe isothermal control. The system
controls outdoor electronic expansion valve opening so that the gas pipe temperature in each
room becomes equal.
(4) Indoor Heat
Exchanger
Thermistor
1. 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 outdoor electronic expansion valve
opening so that the target discharge pipe temperature can be obtained.
2. 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.
3. 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
– 30.2°F (– 1° C)
Ta – Tc
18° F (10° C)
where Ta is the room temperature and Tc is the indoor heat exchanger temperature.
4. 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.
5. In heating operation, the indoor heat exchanger thermistor is used for detecting the
disconnection of the discharge pipe thermistor. When the discharge pipe temperature becomes
lower than the maximum indoor heat exchanger temperature, the discharge pipe thermistor is
judged as disconnected.
6. When only one indoor unit is operating, 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 outdoor electronic expansion
valve openings to obtain the target subcool.
7. 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.
