Mitsubishi Electric R410A, Service Handbook

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[8-10 Troubleshooting Inverter Problems (YLMU) ]
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8-10 Troubleshooting Inverter Problems (YLMU)
8-10-1 Inverter-Related Problems and Solutions
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Replace only the compressor if only the compressor is found to be defective. (Overcurrent will flow through the inverter if the
compressor is damaged, however, the power supply is automatically cut when overcurrent is detected, protecting the inverter
from damage. Make sure that the model selection switches on the outdoor unit (Dip switches SW5-3 through 5-6 on the out-
door unit control board) are set correctly. For switch settings, refer to the following page(s). [7-8-2 Error Code [7101]](page
227)
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Replace only the fan motor if only the fan motor is found to be defective. (Overcurrent will flow through the inverter if the fan
motor is damaged, however, the power supply is automatically cut when overcurrrent is detected, protecting the inverter from
damage.)
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Replace the defective components if the inverter is found to be defective.
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If both the compressor and the inverter are found to be defective, replace the defective component(s) of both devices.
(1) Inverter-related problems: Troubleshooting and remedies
1) The inverter contains a large-capacity electrolytic capacitor in which voltage remains even after the main power is turned off,
so it is dangerous as there is the risk of electric shock . Therefore, before carrying out checks related to the inverter, turn
off the main power, wait a sufficient length of time (5 to 10 minutes), and then check that the voltage for both ends of the elec-
trolytic capacitor has dropped.
2) Before beginning service work, disconnect the fan board connector (CNINV) and the INV board connector (CN1 or CNFAN)
for the outdoor fan. Before disconnecting and connecting a connector, check that the outdoor fan is not rotating and that the
voltage of the main circuit capacitor has decreased to 20 V DC or less. If the outdoor fan rotates due to a strong wind, there
is a
risk of an electric shock because the main circuit capacitor will be charged. Refer to the wiring nameplate for details.
3) To connect wiring to TB7, check that the voltage is 20 VDC or below.
4) Reconnect the connector (CNINV) back to the fan board and reconnect the connector (CN1 or CNFAN) back to the inverter
board after servicing.
5) The IPM on the inverter becomes damaged if there are loose screws are connectors. If a problem occurs after replacing some
of the parts, mixed up wiring is often the cause of the problem. Check for proper connection of the wiring, screws, connectors,
and Faston terminals.
6) To avoid damage to the circuit board, do not connect or disconnect the inverter-related connectors with the main power turned
on.
7) Faston terminals have a locking function. Make sure the terminals are securely locked in place after insertion.
8) When the IPM or IGBT is replaced, apply a thin layer of heat radiation grease that is supplied evenly to these parts. Wipe off
any grease that may get on the wiring terminal to avoid terminal contact failure.
9) Faulty wiring to the compressor damages the compressor. Connect the wiring in the correct phase sequence.
10) When the power is turned on, the compressor is energized even while it is not operating. Before turning on the power, dis-
connect all power supply wires from the compressor terminal block, and measure the insulation resistance of the compressor.
Check the compressor for a graound fault. If the insulation resistance is 1.0 M
ȍ
or below, connect all power supply wires to
the compressor and turn on the power to the outdoor unit. (The liquid refrigerant in the compressor will evaporate by energiz-
ing the compressor.)
11) When tightening the screws, take care that the screws are not loose or overtightened. A contact fault resulting from screw
looseness may cause the generation of heat and fire. Refer to the following page(s). [1-4 Precautions for Wiring](page 13)
12) The control box contains high-temperature parts. Be careful even after shutting down the power.
Press the tab on the terminals to remove them.