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12-5. If a sensor is defective.
12-5-1.Indoor coil temp. thermistor (TH1) is defective.
Alarm Signal (*)
Operation lamp on the front side of the indoor unit will flash on and off when the indoor coil thermistor is defective.
(That is, sensor is SHORT). At the same time the outdoor unit will stop. Indoor unit will operate only for ventilation.
12-5-2.Room temp. thermistor (TH2) is defective.
A. Open
When thermistor opens, the air conditioner will be in the following conditions as the controller tries to detect
extremely low room temperature.
a) In Cooling mode: The air conditioner soon stops and will not start again. (Thermo.OFF)
Neither outdoor fan nor compressor runs.
b) In Heating mode: The air conditioner continues to operate. (Thermo.ON)
Both the outdoor fan and compressor do not stop.
As a result, the room becomes too warm.
B. Short
When thermistor is short, the air conditioner will be in the following conditions as
the controller tries to detect extremely high room temperature.
a) In Cooling mode: The air conditioner continues to operate. (Thermo.ON)
Both the outdoor fan and compressor do not stop.
As a result, the room becomes too cold.
b) In Heating mode: The air conditioner soon stops and will not start again. (Thermo.OFF)
Neither outdoor fan nor compressor runs.
Definition of Open or Short Circuit of Sensor (Thermistor)
Open... A lead wire is broken or disconnected or the circuit inside the temperature sensor is open .
Short... The protective cover of a lead wire has been damaged, and the exposed wire is touching another metal
part, or both lead wires have become exposed and are touching each other. Alternatively, the circuit inside
the temperature sensor is closed.
• Operation lamp on front side of
indoor unit is flashing on and off. (*)
YES
• Replace thermistor.
• Thermistor (TH1 ) is defective.
(That is, sensor is SHORT.)
No
• Function of freeze prevention
continues to work in cooling mode.
YES
• Replace thermistor.
• Thermistor (TH1 ) is not connected
to indoor PCB Ass'y, or its
temperature sensor is defective.
(That is, sensor is OPEN.)
No
Refer to 5-4 "Freeze Prevention"
NOTE
NOTE
Temperature
sensor
Lead
wires
Thermistor Structure
