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U1

U1 - Reverse phase, open phase (Outdoor Unit)

Daikin · Simple Self Diagnosis by Malfunction Code | Daikin

What does U1 mean?

The unit has detected an incorrect phase sequence in the power supply or an open phase, which can damage the system.

Common Causes

  • Incorrect electrical wiring
  • Problem with the main power supply
  • Faulty electrical components

Repair Steps & Checklist

Click steps to track your progress.

  1. 1

    Turn off the power to the unit at the breaker.

  2. 2

    Verify the electrical connections and ensure they are correct for your region.

  3. 3

    Restore power and check if the error clears.

  4. 4

    If the error persists, consult a qualified electrician or HVAC technician.

Browse all codes in this manual (60)
Verified technical data. Last updated: April 2026

Related Faults

6-06-0 - External protection device activated (Heat reclaim ventilator)6-16-1 - Malfunction of PCB (Heat reclaim ventilator)6-26-2 - Ozone density abnormal (Heat reclaim ventilator)
Source: Simple Self Diagnosis by Malfunction Code | Daikin
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