Mitsubishi Electric PQHY-P72ZLMU-A Service Handbook page 353

[ IX Troubleshooting ]
-6- Inverter
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 Heat source unit (Dip switches SW5-3 through 5-8 on the
heat source unit control board) are set correctly. For switch settings, refer to the following page(s). [2] Responding to Error
Display on the Remote Controller)
Replace the defective components if the inverter is found to be defective.
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 INV board has a large-capacity electrolytic capacitor, in which residual voltage remains even after the main power is
turned off, posing a risk of electric shock. Turn off the unit, leave it turned off for at least 10 minutes, and check that the
voltage across FT-P and FT-N terminals on the INV board or the terminals at both ends of the electrolytic capacitor is 20V
or below before checking inside the control box.
(It takes about 10 minutes to discharge electricity after the power supply is turn off.)
2) Control boxes house high-voltage and high-temperature electrical parts. Use caution not to come in contact with them.
3) 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.
4) To avoid damage to the circuit board, do not connect or disconnect the inverter-related connectors with the main power turned
on.
5) Faston terminals have a locking function. Make sure the terminals are securely locked in place after insertion.
6) 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.
7) Faulty wiring to the compressor damages the compressor. Connect the wiring in the correct phase sequence.
8) When the power is turned on, the compressor is energized even while it is not operating. Before turning on the power, discon-
nect 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 or below, connect all power supply wires to
the compressor and turn on the power to the heat source unit. (The liquid refrigerant in the compressor will evaporate by en-
ergizing the compressor.)
9) Read Chapter I [13] Precautions for servicing, and tighten screws to the appropriate torque.Loose screws and poor contact
can result in overheating and fire.
HWE15150
Press the tab on the terminals to remove them.
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