Daikin Mini Split U1 Error Code

Updated 2026-08-29 · review status: manual-verified · reviewed by MiniSplitDecoder Editorial Team Last verified: 2026-08-29

Check your model first

The source record does not specify an exact model family.

Match the model on your equipment label to the linked manufacturer documentation. The same code can mean different things across model families.

Quick answer

U1 means reverse phase or open phase on the outdoor power supply - the three-phase (or detected phase) wiring is wrong or a phase is missing, so the unit refuses to start Clean filters and outdoor clearance, power cycle once, and call a technician if the code returns..

Severity: high · DIY difficulty: intermediate

Safety

Stop at filters, outdoor clearance, and one reset. Do not open panels, measure current, or check refrigerant charge - inverter and refrigerant diagnosis is technician-only.

What U1 means

U1 means reverse phase or open phase on the outdoor power supply - the three-phase (or detected phase) wiring is wrong or a phase is missing, so the unit refuses to start.

Causes, ranked

  1. 1. Power supply wiring fault - reversed or open phase common pro only

    Check: Phase verification requires opening the electrical box and measuring.

    Fix: Technician/electrician: verify phase order and continuity at the disconnect and unit.

  2. 2. Loose power terminal at the disconnect or unit occasional pro only

    Check: Terminal inspection is inside the electrical box.

    Fix: Technician/electrician: retermine the power connections.

  3. 3. Utility-side phase loss after storm or line work occasional DIY

    Check: Check whether other three-phase equipment in the building also fails.

    Fix: If building-wide, call the utility; otherwise schedule HVAC service.

  4. 4. Outdoor PCB phase-detection fault rare pro only

    Check: Board-level diagnosis only.

    Fix: Technician: diagnose the outdoor PCB.

Related codes

Cross-references for the same fault family, by brand:

Daikin U2 · Daikin L6

Commonly searched as: "daikin u1" · "daikin error code u1" · "daikin air conditioner u1"

Sources

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