MITSUBISHI ELECTRIC MUY-GE09NA - Manual (Page 31)

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Is the resistance of thermistor normal?
(Refer to 10-6.1.)
Reconnect the connector of thermistor.
Turn ON the power supply and press EMERGENCY OPERATION switch.
No
Replace the thermistor except RT64. When RT64 is
abnormal, replace the inverter P.C. board.
Does the unit operate for 10 minutes or more
without showing thermistor abnormality?
OK.
(Cause is poor contact.)
Replace the inverter P.C. board.
Thermistor Symbol Connector, Pin No. Board
Defrost (MUZ) RT61 Between CN641 pin1 and pin2
Inverter P.C. board
Discharge temperature RT62 Between CN641 pin3 and pin4
Fin temperature RT64 Between CN642 pin1 and pin2
Ambient temperature RT65 Between CN643 pin1 and pin2
Outdoor heat exchanger temperature RT68 Between CN644 pin1 and pin3
Yes
Yes
No
G Check of outdoor thermistors
H Check of R.V. coil
First of all, measure the resistance of R.V. coil to check if the coil is defective. Refer to 10-4.
In case CN721 is disconnected or R.V. coil is open, voltage is generated between the terminal pins of the connector
although no signal is being transmitted to R.V. coil.
Check if CN721 is connected.
Is there 208/230 VAC between CN721
and on the inverter P.C. board 3
minutes after the power supply is turned
ON?
No
Yes
Replace the inverter
P.C. board.
Replace the 4-way valve.
Unit operates COOL mode even if it is set to HEAT mode.
Is there 208/230 VAC between CN721
and on the inverter P.C. board 3
minutes after the power supply is turned
ON?
Yes
No
Replace the inverter
P.C. board.
Replace the 4-way valve.
Unit operates HEAT mode even if it is set to COOL mode.
Disconnect connector (CN61)
between the compressor and the
intelligent power module.
Turn ON the power supply and
press EMERGENCY OPERATION
switch twice (HEAT mode).
Disconnect connector (CN61)
between the compressor and the
intelligent power module.
Turn ON the power supply and
press EMERGENCY OPERATION
switch once (COOL mode).
Disconnect the connector of thermistor in the outdoor P.C. board (see
below table), and measure the resistance of thermistor.
(MUZ)