L2 Open Phase, 51CM Connector Open, or Input Circuit Fault

What does FA mean?

The L2 phase of the power supply is open, or the 51CM connector on the outdoor unit is disconnected. Alternatively, a general fault has occurred in the outdoor unit's input power circuit, potentially due to issues with rectifiers, filters, or other input components.

1. 1

   Measure voltage between L1-L2, L2-L3, and L3-L1 at the outdoor unit main power terminals — expect balanced 3-phase voltage.

2. 2

   Inspect the 51CM connector on the outdoor unit PCB — verify it is securely seated.

3. 3

   Check continuity of the wiring connected to the 51CM connector using a multimeter.

4. 4

   Measure the incoming AC voltage at the outdoor unit's main power terminals.

5. 5

   Check the fuses or circuit breakers in the input power path to the outdoor unit.