Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 64

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:
−30.6°F (−34.8°C) or less
Short:
215.6°F (102°C) or more
TH8:
Thermistor <Heat sink>
Diagnosis of failure
Yes
Is it a model with internal thermistor?
Check the wiring and connector connection of
TH8.
Is there any abnormality such as
disconnection, looseness or break-
age?
Disconnect the connector to check the resis-
tance of TH8 using a multimeter.
Is the detected resistance normal?
Check the temperature of TH8.
Is the detected temperature normal?
OCH800A_64
No
Yes
No
No
Yes
The detected temperature of TH8 can be displayed by an
operation of SW1 on the outdoor multi controller circuit board.
SW1 Setting
ON
OFF
1 2 3 4 5 6 7 8
No
Yes
Causes and checkpoints
• Disconnection or contact failure of connectors
• Faulty thermistor
• Defective outdoor multi controller circuit board
The black square (■) indicates a switch position.
Connect the wiring/connector properly.
Replace it in the case of breakage.
Replace the thermistor.
Display on LED1,2
Unit
-99.9–999.9 °F
Replace the outdoor multi controller circuit board
(Malfunction of thermistor circuit).
No abnormality
(A connector contact failure is suspected.)