Mitsubishi Electric R410A Service Handbook page 186

[7-5 Error Code Definitions and Solutions: Codes [4000 - 4999] ]
In case of 4226 (For P120, P144, and P168 type units, the fan box's fan board is applicable)
Check the voltage at CNVDC on the Fan board while the inverter is stopped and if it is 420 V or above, check the following
items.
1) Check the voltage at CN72 on the control board.
2) Check the noise filter coil connections and for coil burnout.
3) Check the wiring connections between the following sections
Between the noise filter board INV board and the Fan board.
4) Check contents 4220
Replace the Fan board if no problems are found.
Check the voltage at CNVDC on the Fan board while the inverter is stopped and if it is less than 420 V, check the following
items.
1) Check between noise filter board, inverter board, connector board, and fan board.
2) Check contents 4220
Replace the Fan board if no problems are found.
(3) Control board failure
Check that 12VDC is applied to connector CN72 on the control board while the inverter is operating. If voltage is absent or
the wrong voltage is applied, check the fuse F01. Replace the control board if no problems are found with the fuse.
For inverter-related error codes, refer to the following page(s). [8-10 Troubleshooting Inverter Problems (YLMU)](page 276)
HWE14080
Go to 3).
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