Daikin air conditioner error codes

How Daikin Error Codes Work

• Daikin systems have alphanumeric codes (letters + numbers) like A5, U4, J3, etc.
• They show up on displays (indoor unit, remote, PCB, fault LED blink codes) when the system detects something outside normal operating range.
• The codes are grouped by indoor unit issues, outdoor unit issues, system-communication / safety / power issues, sensor and thermistor issues, etc.

Common Error Codes You Mentioned with Explanation

• U4 – Communication error between indoor and outdoor units. Signals aren’t being shared correctly; could be wiring issues or PCB failure.
• A5 – Freeze protection (in cooling) / high pressure in heating mode. Often triggered by low airflow (dirty filters), blocked air path, very low refrigerant, or sensor issues.
• J3 – Outdoor discharge pipe temperature sensor fault; could be bad thermistor or wiring.

Full/Expanded List of Daikin Error Codes & Troubleshooting Guide

Below is an extended list of error codes, their meaning, typical causes, and what to check. Use it to help diagnose and decide whether you can fix it or need a technician.

Code	What It Means / Description	Likely Causes / What to Inspect	What to Do
A-series (Indoor faults, PCB, motor, etc.)
A0	External protection device activated (indoor)	Protection device on terminal strip T1-T2 triggered; overcurrent, safety-switch tripped	Reset device if possible; check external protection wiring and components.
A1	Indoor PCB (control board) defect	Faulty control board, noise interference, defective components	PCB repair or replacement. Check power input stability.
A3	Drain level control / overflow / water level sensor fault	Blocked drain, float switch problem, mis-installation of drain line	Clear drains, check float switch, ensure proper slope of drain hoses.
A4	Freeze protection issue / water temperature too low (water unit)	Low water flow, cold inlet, thermistor bad, water supply issue	Check water supply, flow rates, thermistor readings.
A5	High pressure in heating / freeze protection (cooling)	Dirty filters, blocked airflow, refrigerant issues, heat exchanger thermistor bad	Clean filters, ensure airflow, check refrigerant levels, sensor wiring.
A6	Fan motor locked / overload / overcurrent	Motor jam, obstruction, bad bearings, wiring issue	Inspect fan motor physically, clear obstructions, check motor current.
A7	Swing flap motor fault	Flap mechanism jam, motor failure, connection problem	Test swing flap assembly, check motor and wiring.
A8	Power supply / overcurrent fault (indoor)	Voltage spikes, unstable power, input AC current too high	Check electrical supply, protection devices, stable voltage.
A9	Electronic expansion valve (EEV) fault	EEV coil issue, PCB drive failure, installation error	Check EEV, wiring, voltage, whether properly seated.
AA	Heater overheat / (for heating units)	Heat exchanger too hot, over-load, blocked airflow	Inspect heating elements, airflow, sensors.
AF	Humidifier system problem / water leakage or float switch etc.	Leak, float switch wrong, water path issues	Inspect humidifier / condensate pump, check leaks.
AH	Dust collector / filter cleaning system error	Dirty or clogged air cleaner filter, sensor not detecting properly	Clean or replace filters; test filter sensor.
AJ	Capacity setting / PCB setting error	After replacing PCB, adaptor not installed; mismatch	Confirm proper configuration, PCB matching.
C-series (Sensor / thermistor / fan / panel etc.)
C1	Failure in transmission between indoor PCB and fan PCB	Wiring or connection failure	Check connections, wires, joints.
C4	Liquid pipe thermistor for heat exchanger error	Thermistor open or bad, connector issue	Measure resistance, inspect wiring.
C5	Gas pipe thermistor error	Same as above but on gas line	Check sensor, wiring.
C6	Fan motor control driver / sensor failure	Motor sensor wrong, driver circuit bad	Check driver board, motor sensor.
C7	Front panel flap / louvre or flap motor fault / limit switch problem	Flap binding, limit switch misaligned, motor fail	Inspect flap movement, limit switch position.
C9	Suction air thermistor error	Sensor bad or dislodged, connector loose	Replace or re-connect sensor.
CA	Discharge air thermistor error	Similar to C9 but at discharge air path	Evaluate and test.
CC	Humidity sensor / moisture detection error	Humidity sensor bad, wiring issues	Inspect/replace sensor, test humidity functions.
CJ	Remote controller thermostat / temperature sensor error	Remote controller sensor failing, interference	Change battery/remote, test sensor.
E-series (Outdoor / protection / safety / boards)
E0	Protection devices activated (outdoor)	Outdoor safety device triggered (e.g. overcurrent, safety switch)	Check outdoor protection circuits; reset.
E1	Outdoor PCB defect	Board failure, maybe due to spikes/water damage	Inspect outdoor PCB, replace if needed.
E5	Compressor overheat / heat protection engaged	Compressor is overheating, maybe due to overwork, low refrigerant, blocked airflow around condensing coil	Check refrigerant, airflow, clean condenser.
E6	Compressor start-up error / lock / overcurrent	Compressor can’t start; could be mechanical seize, voltage issue	Listen for noisy attempt to start, check power, inspect compressor.
E7	Outdoor fan motor fault	Fan not spinning, motor issue, wiring	Inspect fan blades, motor wiring, bearings.
E8	Overcurrent input (outdoor)	Voltage surge or too much load, improper wiring	Check mains voltage, supply wiring.
F-series (Pipes / pipe-temperature / pressure etc.)
F3	Discharge pipe temperature abnormal	Sensor error, overheating, blocked airflow, refrigerant issue	Measure actual discharge temp; compare sensor reading.
F6	High pressure control in cooling / refrigerant overcharge	Pressure too high; safety switch trips	Check pressures, ensure correct refrigerant charge.
H-series (Sensors, pressure, detection)
H0	Sensor system malfunction (general)	One or more sensors failing, connectors loose, mismatch	Identify which sensor isn’t working; test.
H6	Position detection sensor error / operation halt due to sensor at the compressor etc.	Bad position sensor, or detection mechanism stuck or miswired	Check detection sensors, wiring.
H8	DC current sensor fault / input current sensor issue	Measurement issue, sensor damaged	Test sensor or current transformer.
H9	Air thermistor / suction air/temp sensor error (outdoor or indoor depending)	Sensor failure or disconnection	Replace or re-connect sensor.
J-series (Pipe / sensor / pressure / thermistor)
J3	Discharge pipe thermistor error / discharge pipe temperature sensor fault	Sensor bad, wiring short/open, misreading	Check the thermistor physically; compare with correct resistance/reading.
J6	Heat exchanger (gas pipe) thermistor sensor error / overheat protection via sensor	Sensor possible failure, heat exchanger issue	Test or replace sensor, check for overheating.
J1 / J2 etc	Pressure sensors / current sensors / remote temperature sensors faults	Loose wires, bad sensor, moisture damage	Inspect sensors and connections.
L-series (Inverter, power transistor, overcurrent, temperature rises)
L3	Temperature rise in electrical parts / switch-box etc.	High ambient temp, obstructed ventilation, overcurrent, PCB overheating	Check for blockage, ensure ventilation, check currents.
L4	High temperature of inverter heatsink (“power transistor temp rise”)	Overload, poor cooling of heatsink, dust buildup	Clean, ensure cooling fans/coil are good.
L5	Output overcurrent / instantaneous current too high	Faulty motors, short circuit, overload	Check circuit, motors, possible short.
System / U-series (Communication, refrigerant, power)
U0	Refrigerant shortage / low pressure drop / or EEV failure in some models	Leaks, under-charge, EEV stuck	Pressure test, refrigerant top-up, EEV inspection.
U1	Reverse phase / open phase / improper power phase (for 3-phase systems)	Wiring mistake at install; phase sequence wrong	Correct the wiring.
U2	Power voltage problem / drop / overvoltage / instability	Poor power supply, voltage dips or surges	Use proper power source, surge protector, check supply.
U4	Communication error indoor-outdoor	Wiring, communication line broken / interfered / PCBs not responding	Inspect communication wiring; replace PCB if needed.
UA	Combination error of indoor/ outdoor / model mismatch	Mismatched units, wrong adaptor, spare parts mismatch	Ensure correct compatible units; reconfigure settings.

What to Check First (Troubleshooting Steps)

1. Power Supply / Wiring
   • Ensure correct voltage, stable supply.
   • Check wiring between indoor and outdoor units especially communication wires.
2. Filters, Airflow & Cleanliness
   • Dirty filters, blocked grilles reduce airflow which can cause freeze errors, high pressure, overheating.
3. Sensors / Thermistors
   • Many codes are sensor related; check if sensors are physically clean, properly connected, no damage.
4. Refrigerant Levels / Pressure
   • Low refrigerant can trigger multiple errors: freeze protection, low pressure, etc. Overcharge or blocked pipes can lead to high pressure or discharge temp errors.
5. PCB / Control Boards
   • If multiple unrelated errors or communication fails, PCB or control module may have failed, or firmware issues.
6. Outdoor Unit Conditions
   • Is the condenser clean? Is fan working? Are there obstructions?
7. Model-Specific Checks
   • Some features like humidifier, dust collector, or optional units require specific sensors/components; if those are installed, check those.

When to Call a Technician

• If error persists after basic checks (clean filters, ensuring power, etc.)
• Errors relating to refrigerant leaks (U0 etc.) need licensed technician.
• Compressor starts-up errors or locking, fan motor faults.
• PCB or inverter module faults.