Mitsubishi Electric MXZ-3C24NA Service Manual page 70

• When heating, room does not get warm.
• When cooling, room does not get cool.
How to check inverter/compressor
Disconnect the terminal of the compressor or the connector (CNMC) between the compressor
and the outdoor power P.C. board. 3 minutes after the power supply is turned ON,
start EMERGENCY OPERATION.
Measure the voltage between each
lead wire leading to the compressor.
U (BLK) - V (WHT)
V (WHT) - W (RED)
W (RED) - U (BLK)
Output voltage:
Is proper output voltage detected?
Yes
Is output balanced?
Yes
Is the input voltage to the outdoor control
P.C. board 370 V or more?
Yes
Turn OFF the power supply of indoor and
outdoor unit, and measure the compressor
winding resistance between the compressor
terminals.
Is the resistance between each terminal normal?
(Refer to 11-5.)
Yes
Reconnect the lead wire of compressor, and turn ON
the power supply to indoor and outdoor unit.
3 minutes later, start EMERGENCY OPERATION.
Clarify the causes by counting time until the inverter stops.
0 to 10 seconds: compressor layer short
10 to 60 seconds: compressor lock
60 seconds to 5minutes: refrigerant circuit defective
5 minutes or more: normal
OBH702A
or more before measuring the voltage.
number of indoor units to be operated.
No
No
No
Replace the outdoor power P.C. board.
No
Replace the compressor.
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