OCH791 _52
5110 (U4): Heat sink temperature thermistor (TH8) open/short
Abnormal points and detection methods
TH8 (Internal thermistor) is found to be open/short.
• Y model
Open:
−34.8°C [−30.6°F] or less
Short:
102°C [215.6°F] or more
TH8:
Thermistor <Heat sink>
Causes and checkpoints
• Disconnection or contact failure of connectors
• Faulty thermistor
• Defective outdoor multi controller circuit board
The black square (■) indicates a switch position.
Diagnosis of failure
Connect the wiring/connector properly.
Replace it in the case of breakage.
Replace the thermistor.
Replace the outdoor multi controller circuit board
(Malfunction of thermistor circuit).
No abnormality
(A connector contact failure is suspected.)
Check the wiring and connector connection of
TH8.
Disconnect the connector to check the resis
-
tance of TH8 using a multimeter.
Check the temperature of TH8.
The detected temperature of TH8 can be displayed by an
operation of SW1 on the outdoor multi controller circuit board.
ON
OFF
1 2 3 4 5 6 7 8
SW1 Setting
Display on LED1, 2
Unit
–99.9–999.9
°C
Is it a model with internal thermistor?
Is there any abnormality such as
disconnection, looseness or break
-
age?
Is the detected resistance normal?
Is the detected temperature normal?
Yes
Yes
No
No
No
No
Yes
Yes
