Daikin fault codes

Likely causes, most common first

1. No fault stored in the control
2. The problem is intermittent and cleared itself
3. The complaint is a comfort or airflow issue rather than a control fault

What you can safely check yourself

• Check the remote is in the mode and temperature you expect
• Check and replace the indoor unit air filter
• Make sure supply and return airflow at the indoor unit is not blocked by furniture or curtains
• Check the outdoor unit is clear of leaves, snow and debris

Likely causes, most common first

1. Wrong models interconnected (indoor and outdoor unit are not a matched pair)
2. Defective indoor unit PCB
3. Disconnection of a connector on the indoor PCB
4. Reduction of power supply voltage

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once
• Check the breaker for the indoor and outdoor unit is fully on

Likely causes, most common first

1. Defective drain pump
2. Improper drain piping work
3. Clogged drain piping
4. Defective float switch
5. Defective indoor unit PCB
6. Defective short circuit connector X15A on indoor unit PCB

What you can safely check yourself

• Check the condensate drain line outlet outside for a clog, kink or blockage
• Check for water pooling under the indoor unit and shut the system off if it is overflowing
• Turn the system off at the breaker or disconnect switch and back on once after the drain is clear

Likely causes, most common first

1. Clogged air filter of the indoor unit
2. Short-circuited air (discharge air blowing straight back into the return)
3. Dust accumulation on the indoor heat exchanger
4. Defective indoor heat exchanger thermistor
5. Defective indoor unit PCB

What you can safely check yourself

• Check and clean or replace the indoor unit air filters - this is the number one cause
• Make sure nothing is blocking the indoor unit's air intake or discharge (furniture, curtains, shelving)
• Give the unit time to thaw with the fan running before restarting
• Check the outdoor unit is not buried in snow or leaves

Likely causes, most common first

1. Layer short inside the fan motor winding
2. Breaking of wire inside the fan motor
3. Breaking of the fan motor lead wires
4. Defective capacitor of the fan motor (AC motor / FDXS ducted units)
5. Reduction of power supply voltage (AC motor units)
6. Defective indoor unit PCB

What you can safely check yourself

• Check nothing has fallen into or is jamming the indoor unit's air outlet
• Check and clean or replace the air filters
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of connector
2. Defective thermistor
3. Defective indoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of connector
2. Thermistor corresponding to the error code is defective
3. Defective indoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Defective reduction motor
2. Malfunction or deterioration of the front panel mechanism
3. Defective limit switch

What you can safely check yourself

• Check nothing is physically blocking the front panel from opening or closing
• Turn the system off at the breaker or disconnect switch and back on once, then watch whether the panel moves

Likely causes, most common first

1. Disconnection of connector
2. Defective thermistor
3. Defective indoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of connector
2. Defective humidity sensor
3. Defective indoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of connector
2. Breaking of wires
3. Defective sensor(s)
4. Defective sensor kit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Defective room temperature thermistor in the wired remote controller
2. Defective wired remote controller PCB
3. External factor such as noise

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once and see whether CJ comes back

Likely causes, most common first

1. Defective outdoor unit PCB
2. Broken harness between PCBs
3. Noise
4. Momentary fall of voltage
5. Momentary power failure

What you can safely check yourself

• Check for a recent power outage or brownout
• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Actuation of the high pressure switch (S1PH)
2. Closed stop valve
3. Disconnection of connector S40 or of the two terminals at the high pressure switch
4. Broken S1PH harness
5. Defective high pressure switch
6. Defective outdoor unit PCB
7. Defective high pressure sensor (multi-split)
8. Instantaneous power failure (multi-split)

What you can safely check yourself

• Check the outdoor unit is not blocked by leaves, snow, plants or a fence and has open space around it
• Check the outdoor coil is not visibly plugged with dirt or cottonwood
• Turn the system off at the breaker or disconnect switch and back on once after clearing anything blocking airflow

Likely causes, most common first

1. Abnormal drop of low pressure (lower than 0.07 MPa)
2. Defective low pressure sensor
3. Defective outdoor unit PCB
4. Stop valve not opened

What you can safely check yourself

• Check and replace the indoor unit air filters (starved airflow drops suction pressure)
• Make sure indoor unit airflow is not blocked
• Check the outdoor unit is clear of snow and debris

Likely causes, most common first

1. Refrigerant shortage
2. Defective stop valve or stop valve left closed
3. Defective discharge pipe thermistor
4. Defective electronic expansion valve or coil
5. Defective four way valve or coil
6. Water mixed in refrigerant
7. Defective outdoor unit PCB
8. Compressor lock or high differential pressure (multi-split)
9. Incorrect UVW wiring (multi-split)

What you can safely check yourself

• Check the outdoor unit has clear airflow and is not blocked by snow, leaves or stored items
• Check and replace the indoor unit air filters
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Compressor locked
2. Compressor harness disconnected

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, leave it off at least 30 seconds, and turn it back on once

Likely causes, most common first

1. Foreign matter stuck in the fan
2. Defective fan motor
3. Defective outdoor unit PCB
4. Fan motor connector disconnected

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, then look through the outdoor unit's fan grille for leaves, ice, plastic bags or other debris
• Clear away anything blocking the fan or the coil from outside the cabinet
• Turn the power back on once after clearing the blockage

Likely causes, most common first

1. Outdoor temperature is out of operation range
2. Defective compressor
3. Defective power module
4. Defective outdoor unit PCB
5. Short circuit

What you can safely check yourself

• Check whether the outdoor temperature is far outside the unit's rated operating range
• Check the outdoor unit has clear airflow and is not blocked by snow, leaves or a cover
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of connectors for electronic expansion valve Y1E or Y3E
2. Defective moving part of electronic expansion valve
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Disconnection of four way valve coil
2. Defective four way valve, coil, or harness
3. Defective outdoor unit PCB
4. Defective thermistor
5. Refrigerant shortage
6. Water mixed in refrigerant
7. Defective stop valve

What you can safely check yourself

• Confirm the remote is actually set to the mode you expect (heat vs cool)
• Check and replace the indoor unit air filters
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Refrigerant shortage
2. Defective discharge pipe thermistor (or outdoor heat exchanger / outdoor temperature thermistor)
3. Defective electronic expansion valve or coil
4. Defective four way valve
5. Water mixed in refrigerant
6. Defective stop valve
7. Defective outdoor unit PCB

What you can safely check yourself

• Check the outdoor unit is clear of leaves, snow and debris and has clearance around it
• Check and replace the indoor unit air filters
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. The installation space is not large enough
2. Dirty outdoor heat exchanger
3. Defective outdoor fan motor
4. Defective stop valve
5. Defective electronic expansion valve or coil
6. Defective outdoor heat exchanger thermistor
7. Defective outdoor unit PCB
8. Refrigerant overcharge (multi-split)

What you can safely check yourself

• Check the outdoor coil is not blocked with dirt, cottonwood, leaves or grass clippings
• Clear shrubs, fencing or stored items crowding the outdoor unit
• Check the outdoor fan is running and not obstructed
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Abnormal operation due to air intrusion into the refrigerant circuit
2. Defective discharge pipe thermistor
3. Abnormal deformation of piping in the outdoor unit

What you can safely check yourself

• Shut the system off at the breaker or disconnect switch and leave it off until a technician can look at it

Likely causes, most common first

1. Broken or disconnected harness
2. Disconnection of the compressor harness
3. Disconnection of reactor
4. Defective outdoor unit PCB
5. Defective compressor
6. Supply voltage obviously low or high

What you can safely check yourself

• Check the breaker or disconnect for the outdoor unit is fully on
• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Start-up failure caused by the closed stop valve
2. Input voltage is outside the specified range
3. Disconnection of the compressor relay cable
4. Defective compressor
5. Defective outdoor unit PCB

What you can safely check yourself

• Check the breaker or disconnect for the outdoor unit is fully on
• Turn the system off at the breaker or disconnect switch, leave it off at least 30 seconds, and turn it back on once

Likely causes, most common first

1. Defective outdoor unit PCB
2. Defective power module
3. Broken or disconnected wiring
4. Defective reactor

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Disconnection of the connector for the thermistor
2. Defective thermistor corresponding to the error code
3. Defective outdoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of the connector for the thermistor
2. Defective discharge pipe thermistor
3. Defective heat exchanger thermistor (outdoor coil in cooling, indoor coil in heating)
4. Defective outdoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of thermistor
2. Defective suction pipe thermistor (R3T, R5T)
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of the connector for the thermistor
2. Defective outdoor heat exchanger thermistor
3. Defective outdoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of thermistor
2. Defective outdoor liquid pipe thermistor (R7T)
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of the connector for the thermistor
2. Defective thermistor
3. Defective outdoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of thermistor
2. Defective subcooling heat exchanger gas pipe thermistor (R6T)
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of the high pressure sensor connector
2. Defective high pressure sensor
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Disconnection of the low pressure sensor connector
2. Defective low pressure sensor
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. IPM (power module) failure
2. Current sensor failure
3. Failure of IGBT or drive circuit
4. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Defective outdoor fan motor
2. Short circuit (hot discharge air recirculating into the unit)
3. Defective radiation fin thermistor
4. Disconnection of connector
5. Defective outdoor unit PCB

What you can safely check yourself

• Check the outdoor unit has clear space around it and is not enclosed or crowded by fencing or plants
• Check the outdoor coil is not blocked with debris
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Defective outdoor fan motor
2. Short circuit (hot air recirculating into the outdoor unit)
3. Defective radiation fin thermistor
4. Disconnection of connector
5. Defective outdoor unit PCB
6. Silicon grease not applied properly on the radiation fin after replacing the outdoor unit PCB

What you can safely check yourself

• Check the outdoor unit is not enclosed, crowded or blowing its own hot air straight back into itself
• Clear leaves, grass and debris from the outdoor coil and around the base
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Poor installation condition
2. Closed stop valve
3. Defective power module
4. Wrong internal wiring
5. Abnormal power supply voltage
6. Defective outdoor unit PCB
7. Defective compressor

What you can safely check yourself

• Check the outdoor unit has clear airflow and adequate clearance
• Turn the system off at the breaker or disconnect switch, leave it off at least 30 seconds, and turn it back on once

Likely causes, most common first

1. Compressor overload
2. Compressor coil disconnected
3. Defective main PCB (A1P)

What you can safely check yourself

• Check the outdoor unit is clear of debris and has proper airflow
• Check and replace the indoor unit air filters
• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Large pressure difference before starting the compressor (unsatisfactory pressure equalization)
2. Defective compressor
3. Defective main PCB (A1P)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, leave it off a few minutes so pressures equalize, and turn it back on once

Likely causes, most common first

1. Defective main circuit capacitor
2. Improper main circuit wiring
3. Defective main PCB (A1P)

What you can safely check yourself

• Check both legs of the outdoor unit breaker are on and there has not been a partial power outage

Likely causes, most common first

1. Defective radiation fin thermistor
2. Defective outdoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch and back on once

Likely causes, most common first

1. Refrigerant shortage (refrigerant leakage)
2. Closed stop valve
3. Disconnection of the discharge pipe, indoor or outdoor heat exchanger, room or outdoor temperature thermistor
4. Poor compression performance of compressor
5. Defective electronic expansion valve
6. Refrigerant system clogging / incorrect piping (multi-split)

What you can safely check yourself

• Check and replace the indoor unit air filters
• Check the outdoor unit is clear of snow, leaves and debris
• Note whether cooling or heating has been getting gradually weaker over weeks - that pattern points to a leak

Likely causes, most common first

1. Supply voltage is not as specified
2. Momentary fall of voltage
3. Noise
4. Disconnection of compressor harness
5. Defective DC voltage detection circuit
6. Defective over-voltage detection circuit
7. Defective PAM control part

What you can safely check yourself

• Check whether the house has had brownouts, flickering lights or a recent utility outage
• Check the breaker or disconnect for the indoor and outdoor units is fully on
• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Check operation was never executed after installation

Likely causes, most common first

1. Wiring error
2. Breaking of the connection wires between the indoor and outdoor units (wire No. 3)
3. Defective outdoor unit PCB
4. Defective indoor unit PCB
5. Disturbed power supply waveform

What you can safely check yourself

• Check the breaker or disconnect for the outdoor unit is on - the indoor unit will report U4 if the outdoor unit has no power
• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Connection of two MAIN remote controllers when using two controllers
2. Defective indoor unit PCB
3. Defective remote controller
4. Signal transmission error caused by noise

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Defective outdoor unit PCB
2. External factor such as electrical noise

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Remote controller is set to SUB when only one controller is used
2. Connection of two SUB remote controllers
3. Defective remote controller PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Improper connection of transmission wiring between indoor and outdoor unit
2. Defective indoor unit PCB in another zone
3. Defective electronic expansion valve in an indoor unit of another zone

What you can safely check yourself

• Turn every indoor unit on and note which zone shows the fault
• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once
• Wait at least 2 minutes before reading the code again - the manual says a fresh U9 needs 2 minutes to settle

Likely causes, most common first

1. Wrong models interconnected
2. Wrong wiring of connecting wires
3. Wrong indoor unit PCB or outdoor unit PCB mounted
4. Defective indoor unit PCB
5. Defective outdoor unit PCB
6. Excess of connected indoor units (multi-zone)
7. Mismatching of the refrigerant type of indoor and outdoor unit (multi-zone)
8. Outdoor unit PCB setting not performed after replacing with a spare parts PCB (multi-zone)

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Address duplication of centralized remote controller
2. Defective indoor unit PCB

Likely causes, most common first

1. Transmission error between optional controllers for centralized control and the indoor unit
2. Connector for setting master controller is disconnected
3. Defective PCB of centralized remote controller
4. Defective indoor unit PCB

What you can safely check yourself

• Turn the system off at the breaker or disconnect switch, wait a minute, and turn it back on once

Likely causes, most common first

1. Stop valve is left closed
2. Improper connection of transmission wiring between indoor unit and outdoor unit
3. Failure to execute check operation
4. Defective indoor unit PCB

Likely causes, most common first

1. Improper connection of transmission wiring between indoor and outdoor unit
2. Defective indoor unit PCB
3. Defective main PCB (A1P)

What you can safely check yourself

• If the system was just powered up for the first time, allow at least 12 minutes for auto-addressing before reading the code again

Likely causes, most common first

1. A protection device of the indoor or outdoor unit is activated
2. A thermistor (temperature sensor) malfunction
3. A signal transmission error between the indoor and outdoor units

What you can safely check yourself

• Check and replace the indoor unit air filters
• Make sure indoor airflow and the outdoor unit are not blocked
• Check the breaker or disconnect for both the indoor and outdoor unit is fully on
• Retrieve the actual error code: hold the remote's TIMER CANCEL button for 5 seconds, then press it repeatedly until you hear a long beep - the two characters shown are the code