Mitsubishi Electric MXZ-18TV Service Manual page 25

F F Check of outdoor unit thermistor
Start
Disconnect the connector in the outdoor electronic control P. C. board (see below table),
and measure the resistance of thermistor to check whether the thermistor is normal or not.
Normal
Reconnect the connector (CN661, CN663 and CN664) and disconnect the lead wire leading to the compressor.
Turn on power supply to the indoor and outdoor unit. Three minutes later EMERGENCY OPERATION starts.
Does thermistor operate 10 minutes or more though the
thermistor abnormality is not displayed?
Yes
Normal
Thermistor
Discharge temperature thermistor
Defrost thermistor
Evaporation temperature thermistor
Gas pipe temperature A thermistor
Gas pipe temperature B thermistor
Fin temperature thermistor
G G Check of outdoor fan motor
Start
Check the connection of connector (CN851) in the fan motor relay connector and outdoor electronic control P. C. board
at the noise filter P. C. board and connector (CN901) in the noise filter board.
Disconnect the fan motor connector, and measure the resistance of the
fan motor winding to check the winding characteristic.
Normal
1. Disconnect the lead wire leading to the compressor. Turn on power supply to the
indoor and outdoor unit. Three minutes later, EMERGENCY OPERATION starts.
2. Check the voltage between pin 1 and pin 4, pin 1 and pin 5 at the fan motor connector.
Is there voltage of 230V AC?
No
1. Turn off power supply of the indoor and outdoor unit, and disconnect the connector
(CN851).
2. Is the voltage 0V, when the voltage between CN851 pin3 (+), pin7 (-), pin6 (-) are
measured after the power supply is turned on the outdoor unit?
Yes
Is there voltage of 12V DC between CN851 pin3 (+) and pin6 (-), when power supply
turns on the indoor unit and EMERGENCY OPERATION starts in three minutes.
Yes
Replace the noise filter P. C. board
No
Replace the outdoor electronic
control P. C. board.
Symbol Connector, Pin No.
Between CN663 pin3 and pin4
RT61
RT62 Between CN663 pin1 and pin2
RT63 Between CN663 pin5 and pin6
RT65 Between CN661 pin1 and pin2
RT66 Between CN661 pin3 and pin4
RT67 Between CN664 pin1 and pin2
Yes
25
Abnormal
Replace the thermistor
Abnormal
Replace the fan motor
Replace the oudtoor
No
electronic control P. C.
board
No