Mitsubishi Error Code 4102: Power Phase Detection Failure / Supply Error

Quick Answer — Mitsubishi Error Code 4102

Error code 4102 on Mitsubishi CITY MULTI outdoor units indicates a power phase detection error — the inverter has sensed an open, reversed, or unstable three-phase supply.

Most common causes: voltage imbalance or missing phase (40 %), reversed wiring after service (35 %), and loose terminal connections (20 %).

The system shuts down instantly to protect the compressor and inverter transistors.

Turn off power, confirm all fuses and breakers are intact, and measure line-to-line voltage balance.

Average repair cost: $300 – $700; complex inverter or contactor faults can reach $1 200 – $1 500.

Fixair technicians provide rapid phase-detection and voltage-balance correction.

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What 4102 Means

Error 4102 occurs when the outdoor unit’s power detection circuit identifies irregular voltage between L1, L2, and L3.

CITY MULTI inverters require stable three-phase power within ±10 % tolerance.

Any imbalance or phase loss can overheat compressors and blow inverter fuses, so the controller halts operation immediately.

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Main Causes of 4102

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1. Open or Missing Phase (≈ 40 %) — One power leg is not energized due to fuse or breaker failure.
2. Reversed Phase Connection (≈ 35 %) — Wires reconnected incorrectly after service.
3. Loose or Corroded Terminal (≈ 20 %) — Poor contact causes voltage drop.
4. Voltage Imbalance (> 10 % deviation) (≈ 5 %) — Unequal power input between phases.

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Immediate Safety Steps

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1. Turn off power to the outdoor unit.
2. Measure voltage between all three legs (L1-L2, L2-L3, L3-L1).
3. Confirm all readings are within 400–440 V AC for 400 V systems.
4. Check for reversed phase order using a phase-rotation meter.
5. Tighten all terminal screws and inspect for discoloration.
6. If power readings fluctuate, contact Fixair immediately for phase testing.

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Repair Costs and Timeframes (2025)

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• Tightening / re-terminating supply wiring — $300 – $400 (1–2 h)
• Replacing fuse, breaker, or contactor — $450 – $700 (2–3 h)
• Inverter or PCB repair due to surge — $1 200 – $1 500 (3–5 h)
• Most cases are resolved the same day after voltage stabilization and polarity verification.

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Prevention Tips

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• Use phase monitors or voltage relays to detect imbalance early.
• Retorque main power terminals every 12 months.
• Verify phase rotation after electrical work or new installations.
• Avoid running multiple large motors on the same circuit.
• Schedule Fixair preventive inspections annually.

Proper maintenance prevents ≈ 95 % of phase-related faults.

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Frequently Asked Questions

Is error 4102 dangerous?

Yes. It indicates unstable or missing power that can destroy compressors or inverters if not fixed.

Can I reset it myself?

Only after verifying voltage and phase order are correct. Resetting without testing risks further damage.

How much does it cost to fix?

$300 – $700 for wiring or fuse repair; $1 200 – $1 500 for inverter or contactor replacement.

How long does it take?

1 – 3 hours for minor issues, up to 5 hours for inverter board replacement.

Will it return?

Not if voltage monitoring and terminal retorquing are performed during maintenance.

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Summary

Error code 4102 signals a power phase detection failure in Mitsubishi CITY MULTI systems.

It protects the compressor from voltage imbalance, open phase, or reversed wiring.

Shut off power and test supply voltage before restarting.

Most issues cost under $700 to fix and are resolved within hours.

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