Mitsubishi Electric MXZ-2B20NA Service Manual page 29

• When thermistor is abnormal.
Check of outdoor thermistors
Disconnect the connector in the following table and
measure the resistance of the thermistor to check
whether the thermistor is normal or not. (Refer to 11-7.)
Normal
Reconnect the connector in the following table and
disconnect the lead wire leading to the compressor.
3 minutes after turning ON the power supply,
start EMERGENCY OPERATION.
Does the unit operate 10 minutes or more without
showing thermistor abnormality ?
Yes
Normal
Thermistor
Defrost
Discharge temperature
Outdoor heat exchanger temperature
Ambient temperature
Fin temperature
• Fan motor does not operate or stops operating shortly after starting the operation.
Check of outdoor fan motor
Disconnect CN932 from the outdoor
electronic control P.C. board, and measure
the resistance of the outdoor fan motor.
Is the resistance of outdoor fan motor
normal? (Refer to 11-5.)
No
(Fixed to either 5 V or 0 V DC)
Replace the outdoor fan motor.
Abnormal
No
Replace the outdoor electronic control
P.C. board or the outdoor power board.
Symbol Connector, Pin No.
RT61 Between CN661 pin1 and pin2
Between CN661 pin3 and pin4
RT62
RT68 Between CN661 pin7 and pin8
RT65 Between CN663 pin1 and pin2
Between CN3 pin1 and pin2
RT64
Yes
Turn ON the power supply.
Rotate the outdoor fan motor manually and measure the voltage of
CN931.
Between (+) and
Between (+) and
Between (+) and
No
Does the voltage between each terminal become 5 V DC and 0 V DC
repeatedly ?
No
Does the outdoor fan motor rotate smoothly ?
Replace the outdoor electronic control P.C. board.
29
Replace the thermistor except RT64.
In case that RT64 is abnormal, replace the
outdoor power board since RT64 is combined
with the outdoor power board.
Outdoor electronic control P.C. board
Outdoor power board
(-)
(-)
(-)
Yes
Yes
Board