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9-5. If a sensor is defective.
9-5-1. Indoor coil temp. thermistor (TH1) 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.
In cooling mode: Function of freeze prevention continues to work. That is, the controller turns both compres-
sor and outdoor fan motor periodically ON and OFF for several minutes. (Refer to “8-3.
Freeze Prevention”)
B. Short
When thermistor is shorted, the air conditioner will be in the following conditions as the controller tries to detect
extremely high coil temperature.
In cooling mode: Function of freeze prevention will not work even when the frost builds up on indoor heat
exchanger coil.
9-5-2. 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.
In cooling mode: The air conditioner soon stops and will not start again.
(Thermo. OFF) Neither outdoor fan nor compressor runs.
B. Short
When thermistor is shorted, the air conditioner will be in the following conditions as
the controller tries to detect extremely high coil temperature.
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.
Definition of Open or Short Circuit of Sensor (Thermistor)
When thermistor is shorted, the air conditioner will be in the following conditions as the controller tries to detect
extremely high coil temperature.
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.
NOTE
Temperature
sensor
Lead
wires
Thermistor Structure
000-215 SM (1-56) 7/5/00 2:49 PM Page 52