Mitsubishi Electric R410A Service Handbook page 184

[7-5 Error Code Definitions and Solutions: Codes [4000 - 4999] ]
For 4226 (For P120, P144 and P168 the fan board is applicable.)
When the inverter is stopped, check the fan board ( CNVDC )
1) Check CN72C voltage
2) Check coil (L1 - L3) connection condition and for connection failure
3) Check wire connections, noise filter, inverter board, connector board, fan board. If there are no problems, change
the noise filter board.
Replace the noise filter board, if no problems are found.
If the problem recurs after replacing the noise filter, replace the Fan board.
Check the following items if the voltage is below 253V.
4) Check the CNVDC connector connection.
(3) Control board failure
Confirm that a voltage of 12 VDC is applied to the connector CN72C on the control board during inverter operation.
If voltage is absent, check the fuse F01. If no problems are found, replace the control board.
For inverter-related error codes, refer to the following page(s). [8-9 Troubleshooting Inverter Problems (TLMU)](page 264)
HWE14080
If above 253V, then check as below.
Go to (3).
- 175 - GB