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

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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.

• Loss of power on phase L2.
• Open circuit at the 51CM connector.
• General input circuit fault impacting power supply.

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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.