Mitsubishi Electric MXZ-SM72TAM-U1 Service Manual page 61

5105 (U4): Outdoor liquid pipe temperature thermistor (TH3) open/
Abnormal points and detection methods
TH3 is found to be open/short.
(The open/short detection is disabled for 10 seconds to 10
minutes after compressor starts, during defrosting opera-
tion, or for 10 minutes after returning from the defrosting
operation.)
Open:
−40°F (−40°C) or less
Short:
194°F (90°C) or more
TH3:
Thermistor <Outdoor liquid pipe>
Diagnosis of failure
Check the wiring and connector connection of
TH3.
Is there any abnormality such as
disconnection, looseness or break-
age?
Disconnect the connector to check the resis-
tance of TH3 using a multimeter.
Is the detected resistance normal?
Check the temperature of TH3.
Is the detected temperature normal?
OCH800A_61
short
Yes
No
No
Yes
The detected temperature of TH3 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.)