MXZ-SM36NAMHZ Service Manual

72
OCH789
Check code
Abnormal points and detection methods Causes and checkpoints
When the thermistor temperature of -24°F[-31.1°C] or below has
continuously been detected for 3 minutes during heating operation
(during compressor operation), the unit makes an error stop and "3121"
appears on the LED1 and LED2.
The compressor restarts when the thermistor temperature is -14°F
[-25.6°C] or above.
If the unit is turned OFF, the outdoor temperature error will be canceled.
Outdoor air temperature
Thermistor failure
Wire failure
Defective outdoor controller board
●Diagnosis of defects
Make sure to turn the power OFF before connecting/disconnecting any connectors, or replacing boards.
Diagnosis Remedy
3121
Out-of-range outside air temperature
Yes
Yes
Yes
No
No
No
Is the outdoor air temperature
-24°F [-31.1°C] or higher?
Is the resistance normal?
Is wire condition normal?
Use in operation range, which is -14°F
[-25.6°C] or more in heating mode.
Replace the TH7.
Remove the abnormal point.
Check the outdoor air temperature.
Check the resistance of TH7.
Check for pinched lead wire, condition of
wire coating and disconnected wire.
Replace the outdoor controller board.