Service Manual

Control Specification SiUS121502E
60 Function and Control
3. Control Specification
3.1 Function of Thermistor
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The illustration is for the 4-room models as representative and have 4 lines
of indoor unit system (A ~ D). The 3-room models have 3 lines (A ~ C) and 2-room models have 2 lines (A ~ B).
(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 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 drops
below the outdoor heat exchanger temperature by more than a certain value, 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
In cooling operation, the gas pipe thermistor is used for gas pipe isothermal control. The system
controls electronic expansion valve opening so that the gas pipe temperature in each room
becomes equal.
Four way valve
Compressor
EVC
EVD
EVB
EVA
(1)
(2)
(3)
(4)
(5)
(R17360)
DCBA
Electronic
expansion valve