Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 62

5106 (U4): Ambient temperature thermistor (TH7) open/short
Abnormal points and detection methods
TH7 is found to be open/short
Open:
−40°F (−40°C) or less
Short:
194°F (90°C) or more
TH7:
Thermistor <Ambient>
Diagnosis of failure
Check the wiring and connector connection of
TH7.
Is there any abnormality such as
disconnection, looseness or break-
age?
Disconnect the connector to check the resis-
tance of TH7 using a multimeter.
Is the detected resistance normal?
Check the temperature of TH7.
Is the detected temperature normal?
OCH800A_62
Yes
No
No
Yes
The detected temperature of TH7 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.)