ErrorCodeDoctor
Daikin · Air Conditioner

Daikin Air Conditioner U1 error code

Difficulty: Medium · Cost: $0–$200 · Duration: 5–10m

The U1 error means your Daikin air conditioner detected a reverse phase or open phase in the three-phase power supply. For single-phase residential units this typically indicates an open phase — one leg of the power supply is missing. Check the circuit breaker and power supply to the outdoor unit. Contact an electrician if the wiring needs inspection.

Common causes

  • Power supply wiring is connected in reverse phase order
  • One phase of the power supply (T phase) is open or disconnected
  • Outdoor unit PCB has a fault

How to fix it

  1. 1

    Check the circuit breaker for the outdoor unit and make sure it is fully on

  2. 2

    Check that the power supply wiring to the outdoor unit is correct and not reversed

  3. 3

    If wiring is correct and the error persists contact a qualified technician or a licensed electrician

Related Daikin Air Conditioner error codes

1

A0

An external protection device connected to the indoor unit has been activated

hard
2

A1

A fault was detected in the indoor unit PCB (control board)

hard
3

A3

The drain level control system has detected an abnormality — drain may be clogged

medium
4

A5

Freeze-up protection (cooling) or high pressure control (heating) has activated — check the air filter

easy

U1 error — frequently asked questions

What does the U1 error mean on a Daikin air conditioner?

Reverse phase or open phase detected in the power supply

What causes the U1 error?

The U1 error is usually caused by: Power supply wiring is connected in reverse phase order; One phase of the power supply (T phase) is open or disconnected; Outdoor unit PCB has a fault.

Can I fix the U1 error myself?

It's possible for a moderately handy person, but budget 5–10m and expect some disassembly.

How much does it cost to fix the U1 error?

Fixing the U1 error on a Daikin air conditioner typically costs $0–$200, depending on parts and whether you do it yourself or hire a technician.

Is it safe to keep using my air conditioner with the U1 error?

In most cases yes, but it's best to address the U1 error soon — see the fix steps below to resolve it.