Mitsubishi Electric HP120TNU-A Service Handbook page 215

[7-8 Error Code Definitions and Solutions: Codes [6000 - 6999] ]
(2) Troubleshooting problems for indoor units (B)
(1) When the power supply unit for transmission lines is used
and the male power supply connector is connected to the
female power supply switch connector (CN40) for the
transmission line for centralized control
(2) Disconnection or shutdown of the power source of the
power supply unit for transmission line
(3) System controller (MELANS) malfunction
52
- chapter 7
Cause Check method and remedy
1) Check voltage of the transmission line for central-
ized control.
20 V or more: Check (1) on the left.
Less than 20 V: Check (2) on the left.
2) Check the causes of the error in items (1) through
(3) in the "Cause" column.
HWE18220_GB