What It Means
Open phase on L2 power leg or 51CM overcurrent relay connector.
Mitsubishi Electric All Systems
Mitsubishi Electric Error Code FA
Troubleshooting guide for the Mitsubishi Electric system fault FA.
Possible Causes
- Loose or corroded L2 terminal connection at contactor or breaker.
- Blown fuse or tripped breaker on L2 supply leg.
- Damaged or disconnected 51CM current-sensor connector.
- Failed 51CM compressor overcurrent relay or sensor.
- Incoming utility power supply phase loss or imbalance.
Not sure which one it is — or if it's none of these? Try ACLogics today.
Disclaimer: This information is for general reference. Error codes can vary by model and production year. Always refer to your machine's specific manual and the information printed on the unit itself.
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Full Diagnosis
Error detail: the outdoor control board detects an open condition on the L2 power leg or on the 51CM current-sensor connector feeding the compressor overcurrent relay. Because L2 supplies part of the three-phase compressor drive, the outdoor unit locks out the compressor immediately to prevent single-phasing damage to the windings, and a manual reset is required after the wiring fault is cleared. Unlike F2, which flags a lost L3 leg, or F7, which points to a fault in the reverse-phase detection circuit board itself, FA isolates the problem to either the L2 supply conductor or the 51CM sensor loop rather than the control logic.
All Recorded Causes
Loose or corroded L2 terminal connection at the disconnect, breaker, or compressor contactor. Blown fuse or tripped breaker on the L2 leg. Damaged or disconnected 51CM current-sensor connector or wiring harness. Failed 51CM overcurrent relay/sensor. Loose crimp or corrosion at the terminal block on the outdoor unit main board. Incoming utility power imbalance or a missing leg from the electrical panel.
Verify Before Replacing Parts
- Confirm the exact Mitsubishi Electric model family and default context before acting on a generic code description.
- Confirm filter condition, blower operation, and coil cleanliness before replacing any controls — start by ruling out whether loose or corroded L2 terminal connection at the disconnect, breaker, or compressor contact….
- Measure airflow-related readings that match the symptom, such as temperature split or static pressure, and check whether blown fuse or tripped breaker on the L2 leg.
- After the correction, run the system long enough to confirm the default fault does not return under normal load.
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ACLogics has guided diagnostics for 73 Mitsubishi Electric fault codes and asks the right questions to narrow it down.
