What causes Daikin Mini Split U2?

A drop in supply voltage, such as a brownout, an overloaded circuit, or a long or undersized supply run. ESIE05-03 names a drop to 180 V or less. An instantaneous power failure, for example a flicker during a storm or when the utility switches lines. Daikin lists this as its own cause. An open phase or a phase imbalance on three-phase systems. Daikin's VRV manual checks for an open phase and keeps imbalance within 12 V, and ESIE17-08 flags imbalance over 10%. Faulty main circuit wiring, such as loose or burned connections at the breaker, disconnect or outdoor terminal block. A faulty outdoor unit or inverter control board, including its DC voltage or over-voltage detection circuit, or damaged main circuit parts. On some models, a defective compressor, outdoor fan motor, signal cable connection, or indoor unit board. Daikin's newer manuals check these after the power supply.

How do I fix Daikin Mini Split U2?

Think about what just happened. If U2 appeared right after a storm, a power flicker or a breaker trip, a momentary power failure is the listed cause and a reset often clears it. Do a full power reset: switch off the breakers or disconnect for the outdoor and indoor units, wait a few minutes, then switch them back on. Daikin's R32 Sky Air manual resets U2 by power-resetting the outdoor unit, and notes the indoor unit may need a power reset too. After the reset, give it a few minutes. Daikin's manual notes the compressor restarts on its own after a 3-minute standby when the voltage returns to normal. Notice whether lights dim or other equipment struggles when the system starts. That points at low household or utility voltage rather than the unit itself. Avoid running other heavy loads on the same circuit, and check that the breaker feeding the outdoor unit isn't warm, buzzing or tripping. Don't open the outdoor unit or the disconnect to measure voltage yourself. The inverter capacitors carry high DC voltage that can stay charged after the power is off.

When should I call a pro for Daikin Mini Split U2?

U2 returns after a full power reset. An electrician or HVAC technician measures the supply voltage at the outdoor unit, which is Daikin's first check, along with open phases and wrong wiring. The supply voltage sags or is unbalanced. Daikin's remedy is to fix the power supply first; on three-phase systems the VRV manual wants 380-415 V and imbalance within 12 V. The supply checks out. The technician inspects the main circuit wiring, then tests the outdoor or inverter board, which Daikin says to replace when its DC voltage or over-voltage detection circuit is faulty. On VRV systems, the technician checks compressor insulation resistance, since Daikin's flow replaces the compressor when it reads 100 kΩ or less. Newer models still show U2 after those checks. Daikin's manuals go on to the outdoor fan motor, the indoor unit board and the indoor/outdoor wiring before contacting the helpdesk. The code follows utility problems in your area. Ask the power company to check the voltage at your meter, since a utility-side issue can't be fixed at the unit.

Code: U2🔧 Daikin Mini Split

Daikin Error Code U2: Power Supply Voltage Problem (Meaning, Causes, Fixes)

Q: What does Daikin Mini Split U2 mean?

U2 on a Daikin system means the outdoor unit saw abnormal power: the supply voltage dropped too low (or, on some models, rose too high), power was lost for a moment, or a phase went missing. Daikin's service manuals list low or unstable supply voltage, an instantaneous power failure, an open phase, faulty main circuit wiring, and a faulty outdoor inverter board or damaged main circuit parts, with the compressor and fan motor also checked on newer models. A full power reset and a check for brownouts or storm-related outages are the owner steps; measuring voltage and testing boards need an electrician or HVAC technician. Daikin's service manuals call U2 "Abnormal Power Supply Voltage" (Sky Air and split manuals ESIE05-03 and ESIE13-02) or "Power Supply Insufficient or Instantaneous Abnormality" (VRV manual SiME341909EA). The outdoor unit watches the voltage of the main circuit capacitor inside the inverter along with the incoming supply voltage, and sets U2 when that voltage drops below its range or the power cuts out for even a fraction of a second. The exact limits depend on the model: ESIE13-02 gives about 150-170 VAC (or DC outside 305-380 VDC) for single-phase V3 units, and the VRV manual uses a DC circuit voltage below 380 VDC. Newer R32 Sky Air units (ESIE17-08) show it as U2-00 and also trigger it on an abnormal voltage rise or when the indoor board sees no zero-cross signal for about 10 seconds. Daikin's simple self-diagnosis chart sums U2 up as a malfunction of power supply or instantaneous power failure. It points at the electrical supply first, not at refrigerant.

Reviewed 2026-10-24 · Based on 6 manufacturer & service sources

What the code means

Daikin's service manuals call U2 "Abnormal Power Supply Voltage" (Sky Air and split manuals ESIE05-03 and ESIE13-02) or "Power Supply Insufficient or Instantaneous Abnormality" (VRV manual SiME341909EA). The outdoor unit watches the voltage of the main circuit capacitor inside the inverter along with the incoming supply voltage, and sets U2 when that voltage drops below its range or the power cuts out for even a fraction of a second. The exact limits depend on the model: ESIE13-02 gives about 150-170 VAC (or DC outside 305-380 VDC) for single-phase V3 units, and the VRV manual uses a DC circuit voltage below 380 VDC. Newer R32 Sky Air units (ESIE17-08) show it as U2-00 and also trigger it on an abnormal voltage rise or when the indoor board sees no zero-cross signal for about 10 seconds. Daikin's simple self-diagnosis chart sums U2 up as a malfunction of power supply or instantaneous power failure. It points at the electrical supply first, not at refrigerant.

Likely causes

A drop in supply voltage, such as a brownout, an overloaded circuit, or a long or undersized supply run. ESIE05-03 names a drop to 180 V or less.
An instantaneous power failure, for example a flicker during a storm or when the utility switches lines. Daikin lists this as its own cause.
An open phase or a phase imbalance on three-phase systems. Daikin's VRV manual checks for an open phase and keeps imbalance within 12 V, and ESIE17-08 flags imbalance over 10%.
Faulty main circuit wiring, such as loose or burned connections at the breaker, disconnect or outdoor terminal block.
A faulty outdoor unit or inverter control board, including its DC voltage or over-voltage detection circuit, or damaged main circuit parts.
On some models, a defective compressor, outdoor fan motor, signal cable connection, or indoor unit board. Daikin's newer manuals check these after the power supply.

Safe DIY checks

⚠ Before you start

Turn off the breakers for both the indoor and outdoor units before any inspection. Daikin's manuals warn to turn off the power switch before connecting or disconnecting connectors, or parts may be damaged. The outdoor inverter board holds main circuit capacitors at several hundred volts DC that can stay charged after power is off, so leave voltage measurements and board work to a licensed electrician or HVAC technician.

Think about what just happened. If U2 appeared right after a storm, a power flicker or a breaker trip, a momentary power failure is the listed cause and a reset often clears it.
Do a full power reset: switch off the breakers or disconnect for the outdoor and indoor units, wait a few minutes, then switch them back on. Daikin's R32 Sky Air manual resets U2 by power-resetting the outdoor unit, and notes the indoor unit may need a power reset too.
After the reset, give it a few minutes. Daikin's manual notes the compressor restarts on its own after a 3-minute standby when the voltage returns to normal.
Notice whether lights dim or other equipment struggles when the system starts. That points at low household or utility voltage rather than the unit itself.
Avoid running other heavy loads on the same circuit, and check that the breaker feeding the outdoor unit isn't warm, buzzing or tripping.
Don't open the outdoor unit or the disconnect to measure voltage yourself. The inverter capacitors carry high DC voltage that can stay charged after the power is off.

🛠 When to call a pro

U2 returns after a full power reset. An electrician or HVAC technician measures the supply voltage at the outdoor unit, which is Daikin's first check, along with open phases and wrong wiring.
The supply voltage sags or is unbalanced. Daikin's remedy is to fix the power supply first; on three-phase systems the VRV manual wants 380-415 V and imbalance within 12 V.
The supply checks out. The technician inspects the main circuit wiring, then tests the outdoor or inverter board, which Daikin says to replace when its DC voltage or over-voltage detection circuit is faulty.
On VRV systems, the technician checks compressor insulation resistance, since Daikin's flow replaces the compressor when it reads 100 kΩ or less.
Newer models still show U2 after those checks. Daikin's manuals go on to the outdoor fan motor, the indoor unit board and the indoor/outdoor wiring before contacting the helpdesk.
The code follows utility problems in your area. Ask the power company to check the voltage at your meter, since a utility-side issue can't be fixed at the unit.

Parts that commonly fix it

Always match the part number to your exact model.

⚙

Outdoor unit inverter control board

Replaced when Daikin's diagnosis points at the inverter or main PCB; match the exact outdoor model number before ordering.

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⚙

Multimeter

Used by the technician to check supply voltage and phase balance at the outdoor unit.

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⚙

Main circuit wiring and connections

Loose or burned supply connections are a listed U2 cause; a technician should match wire size to the installation manual.

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Sources

Last reviewed 2026-10-24. Always confirm against the manual for your exact model number.

Daikin Error Code U2: Power Supply Voltage Problem (Meaning, Causes, Fixes)

What the code means

Likely causes

Safe DIY checks

🛠 When to call a pro

Parts that commonly fix it

Outdoor unit inverter control board

Multimeter

Main circuit wiring and connections

Related codes

Sources