Daikin AC Indoor Unit Error Codes (A & C Families): Meaning & Fixes

Daikin's A and C codes are the indoor unit reporting on itself: A covers its hardware — drain, fan, flap, expansion valve, circuit board — and C covers its senses, the thermistors it thinks with. Most indoor codes begin as maintenance stories (a drain that finally clogged, a filter that finally choked the coil) and only a few are true parts failures. This guide walks the indoor families code by code: what each one means, what usually causes it, the owner checks that are genuinely worth doing, and the line where the repair becomes a technician's job.

A3 — drain level abnormal: the water code

A3 is the indoor code owners meet most, and it is a water report, not an electronics report. In cooling, the indoor coil condenses moisture out of the room air all day long; that water drips into a drain pan and leaves through the condensate drain, on pumped models lifted by a small drain pump. A float switch (Daikin calls it S1L) watches the pan level, and when water rises instead of leaving, the switch raises A3 and the unit stops cooling before the pan overflows onto your ceiling. The causes rank themselves: a drain line slimed or blocked at its outlet, a kinked or sagging drain hose, a failed drain pump, and last a stuck or failed float switch. Your checks are external and safe — find where the drain exits, confirm water can drip freely, clear a blocked outlet, and check the hose run for obvious kinks. Stop cooling while A3 is showing; heating and fan modes do not make condensate, but cooling on a full pan is how a code becomes water damage. If the outlet runs clear and A3 returns, the fault is inside the unit — pump, float or pan — and that is technician work with the covers off.

A6 — indoor fan motor fault: no airflow, no cooling

A6 reports the indoor blower: Daikin's chart words it as fan motor lock, overload or overcurrent. The indoor fan is what turns a cold coil into a cold room, so the control watches it closely; a motor that will not turn, turns too slowly, or draws too much current stops the system. Causes are usually physical before they are electronic — a blower wheel fouled with years of dust until it drags, something lodged in the fan, a motor whose bearings have worn out, and only then the motor's drive circuit on the indoor PCB. What you can do is limited but real: switch the unit off, look through the outlet louvre for an obvious obstruction, and check whether the fan spins freely by the gentle air movement when the unit is off — never reach into a powered unit, and never spin the wheel by hand with power on. A unit that hums, shudders or smells hot at start-up is telling you the motor is struggling; stop it. Motors are replaced, not repaired, and the diagnosis between motor and board is a meter job, so A6 that survives a power reset belongs to a technician.

A5 — high-pressure control or freeze-up protection (residential splits)

A5 is the indoor code with two faces, because it guards two opposite failures with one sensor story. In heating mode it is high-pressure control: the indoor coil is the condenser, and if it cannot shed heat — clogged filters, a dirty coil, furniture hard against the unit — pressure and temperature climb until A5 stops the system. In cooling mode it is freeze-up protection: the coil runs colder and colder, frost forms, airflow falls further, and A5 intervenes before the coil becomes a block of ice. Both faces are airflow codes first. Low refrigerant can also freeze a coil, which is why A5 is not purely a cleaning code, but the order of suspicion is fixed: filters, coil cleanliness, blocked inlet or outlet, fan actually running (an A5 with a silent fan is really an A6 story), and only then charge. Clean the filters — properly, washed and fully dried, not shaken — clear the unit's air path, defrost a visibly frosted coil by running fan-only until it is dry, and retry once. An A5 that returns on a clean, clear unit has graduated to refrigerant and sensor diagnosis, which is licensed work.

A1 — indoor PCB failure: the board itself

A1 is the indoor unit's control board reporting its own failure — Daikin's VRV chart specifies it as an EEPROM failure (indoor), the memory chip that holds the board's configuration. Unlike the condition codes around it, A1 does not measure anything in the room or the refrigerant circuit; the referee has blown its own whistle. Surges and nearby lightning are its classic trigger, electrical noise from other equipment can provoke it, and boards also simply age out. The one owner move is a genuine power reset: off at the breaker or isolator for several minutes, not a remote off, then back on and observe. A surge-stunned board sometimes comes back and never repeats; an A1 that returns immediately or within days is a failed board introducing itself. Board replacement is technician work with a sting in the tail — on many models the replacement board needs the model's capacity data set into it, which is exactly the AJ fault below when it is skipped. Quote the full model number when you call: boards are model-specific, and the right board on the truck is the difference between one visit and two.

A9 and AJ — expansion valve and capacity setting: the setup codes

A9 and AJ are the indoor codes that most often follow human intervention rather than wear. A9 is the indoor electronic expansion valve: the motorised valve that meters refrigerant into the indoor coil has a moving part and a coil, and the code means that drive has faulted — a failed valve coil, a connector knocked loose during cleaning or service, or the board output that drives it. The valve is small, but it sits on the refrigerant circuit, so diagnosis and replacement are technician work. AJ is purer still: capacity setting malfunction. The indoor board must know what size unit it is, and that knowledge lives in a capacity adaptor or in data written to the board; AJ means the adaptor is missing, wrong, disconnected, or the data was never set — classically after a PCB replacement where the new board went in blank, or an installation where the adaptor was forgotten. Nothing about AJ is a worn part; it is a configuration debt. The fix is to fit the correct adaptor or write the correct capacity data for the exact model, then re-test — installer work, and a useful code to quote verbatim, because an AJ after recent board work tells the technician exactly which step was missed.

C4 and C5 — the indoor coil's thermistors

The C family is the indoor unit's sensor shelf, and C4/C5 are its coil watchers: C4 is the thermistor on the heat exchanger's liquid pipe, C5 the one on its gas pipe (Daikin's charts name them by their circuit tags, R2T and R3T). Between them they tell the control how the coil is behaving, and freeze protection, capacity control and defrost logic all lean on their readings. A C4 or C5 means the sensor circuit itself is lying — thermistor failed open or shorted, a lead chafed through, or a connector oxidised into a bad contact at the PCB. Daikin's SkyAir chart adds a nuance owners should know: for these sensor codes an abnormal stop may or may not be applied depending on the model — some units stop, others run on with degraded control, hunting temperatures and icing or short-cycling in ways that look like other faults. There is no owner repair here beyond noting the code accurately; thermistors are inexpensive parts, but proving which one has drifted, and reaching it, is the job. A technician tests the sensor's resistance against the model's chart and replaces the sensor or repairs its connection — and a C code that follows water ingress or a pest problem in the unit deserves a mention, because the harness, not the sensor, may be the story.

C9, CA and CJ — the air thermistors, including the one in your remote

Three C codes cover the air the unit breathes and blows. C9 is the suction air thermistor — the sensor at the indoor unit's intake that reads the room's returning air and anchors all temperature control; when it fails, the unit effectively does not know what temperature the room is, so it overcools, undercools or cycles strangely even though every mechanical part is healthy. CA is its partner on the discharge side, reading the air leaving the unit; it supervises how cold or hot the supply air actually is. CJ is the odd one out and the easiest fix in the family: the thermistor inside the remote controller itself has failed. Daikin's SkyAir manual is reassuring about CJ — the remote's own sensor stops working, but temperature control by the indoor unit's sensor continues, so a CJ system still heats and cools; what it needs is a replacement remote controller, dealer-supplied, not a repair inside the wall unit. For C9 and CA the pattern is the same as all thermistor codes: the sensor, its lead or its connector has failed, the part is cheap, and the work is proving and reaching it. Quote the exact code when calling — C9 and CA send the technician to different ends of the same unit.

C1, A7, AF and AH — the smaller indoor codes

Four indoor codes complete the family. C1 is transmission failure between the indoor unit's main PCB and its sub PCB — the one C code that is not a sensor. Two boards that must talk have stopped talking: a loose interconnecting harness, a damaged connector, or a board failing on either side; one power reset is fair, a returning C1 is board-and-harness diagnosis. A7 is the swing flap motor — the louvre that sweeps air around the room has jammed or its motor has failed. Check for a physical obstruction and never force the flap against its motor; the repair is minor but it is a parts job. AF covers water and options: on the VRV chart it is a drain malfunction (drain level above its limit — treat it like A3's sibling and check the drain first), while the SkyAir chart words AF as a humidifier system malfunction on units fitted with one; either way, water is the theme. AH is the dust-collector/air-purifier unit — Daikin's VRV chart calls it the filter dust chamber malfunction — and its mercy is scope: only the purifier function stops, while the air conditioning itself generally keeps running until the element or purifier unit is serviced.

Shared indoor causes: airflow, dirt, water and power

Read across the indoor families and the same four roots keep appearing. Airflow is the first: a filter mat thick enough to read through the fan's behaviour will freeze a coil into an A5, starve a fan into working harder toward an A6, and make honest thermistors report dishonest temperatures that masquerade as C codes. Dirt and water are the second pair — the coil and drain pan live wet by design, so biological growth in the drain is the default A3 story, and moisture creeping into connectors is behind a share of intermittent C and C1 codes that vanish when the unit dries and return in humid weeks. Power is the fourth root: surges write A1s, and a board replaced without its capacity data writes AJ. The maintenance that prevents most of the indoor table is unglamorous and short — filters cleaned on schedule, the drain outlet checked each season, the unit's air path kept clear, and a professional service that actually opens the indoor unit, washes the coil and flushes the drain rather than admiring the filters. When you report an indoor code, add its context: after cleaning, after a storm, first hot day of the year. On indoor codes, timing is diagnostic gold.

When indoor codes need a professional

The owner territory on indoor codes is deliberately narrow: read the code with the remote's diagnosis function, clean the filters, clear the air path and the drain outlet, defrost a frozen coil on fan-only, and power-reset once. Everything else on the A and C pages is a technician's job, for one of three reasons. Water inside the unit (A3/AF that survive an outlet check) means covers off around electrics. Boards and their configuration (A1, AJ, C1) need model-specific parts and data, and a board fitted wrong manufactures new codes. Sensors (the whole C shelf beyond CJ's remote swap) need resistance testing against the model's chart to separate a failed thermistor from a failed harness from a failed board input — three different repairs hiding behind one code. Call promptly rather than eventually for: A3 with any sign of water escaping, A6 with heat or burning smells from the indoor unit, A1 that returns after one proper reset, and any indoor code joined by an outdoor or U code, which usually means the indoor unit is reporting a system problem, not its own. Give the technician the code, the unit number if the controller showed one, and when it happens — that turns a diagnostic visit into a repair visit.

Key takeaways

• Read the code before resetting anything: hold TIMER CANCEL for 5 seconds on a wireless remote and step to the long beep — the code you reset away unrecorded is the diagnosis you pay for twice.
• A3 plus a ceiling stain is a stop-now code: switch cooling off and deal with the water before the electronics.
• Filters first for A5 — washed and fully dry, not shaken; a choked filter manufactures freeze-ups that look like refrigerant faults.
• After any indoor PCB replacement, an AJ in the first days means the capacity setting step was skipped — quote it to the installer verbatim.

Resetting the Daikin air conditioner

Daikin codes are condition reports, not latches to be cleared by ritual: the code clears when its condition clears. Daikin's VRV IV reference guide puts the owner-level reset plainly — depending on the level of the malfunction code, you can reset the code by pushing the ON/OFF button; if it will not reset, ask your installer. The fuller reset is a power reset at the isolator/breaker: switch the system off for several minutes (both indoor and outdoor units — on a split they are usually on one isolator), then back on and let it run; Daikin's manuals note the system does not restart instantly (a safety device holds the compressor off for about 3 minutes, and a VRV system can take up to about 12 minutes after power-on to finish its communication/addressing checks). Fault history is separate from the live code: on wired remote controllers the stored malfunction history shown in inspection (check) mode is cleared deliberately — hold the ON/OFF button for 5 seconds or more while in inspection mode, and the code flashes twice, changes to '00' (normal) and the unit number to '0' before the display returns to normal mode. Never clear history before you have written the code down, and never treat a reset as a repair: a code that returns after a clean power reset is a confirmed, present fault.

Frequently asked questions

Related guides

Facts on this page were checked against manufacturer documentation: www.daikin.com.mt · daikinac.com · www.daikin.ch · www.manualshelf.com · www.manualshelf.com · www.manualshelf.com · mcgrp.ru · mcgrp.ru · dwt-front-dev.daikincomfort.com