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Fujitsu
Fujitsu groups its codes by system of origin. A codes come from the indoor unit, C codes come from the indoor sensors and drain protection, and E codes come from the outdoor unit. Knowing the letter narrows the search to one half of the system, which is most of the diagnostic work done before anyone arrives.
| Code | What it means | What to check first |
|---|---|---|
| A0 | External protection device activated | Not a fault in itself. It is a shutdown, so the cause has to be traced at the unit |
| A1 | Indoor circuit board malfunction | Supply voltage and connections before the board is condemned |
| A3 | Abnormal drainage | The drain pan, the drain line and the fall. This is a water fault, not a cooling fault |
| A5 | Sensor malfunction | Sensor resistance against ambient temperature, then the plug and loom |
| A6 | Outdoor unit connection issue | The interconnecting cable and terminations between indoor and outdoor |
| A7 | Fan motor malfunction | Free rotation first, then the motor and its control circuit |
| A9 | Swing flap motor malfunction | The flap motor and its linkage. Usually a comfort nuisance, not a cooling failure |
| C5 | Freezing detection | Airflow restriction or low charge. Both need testing, neither needs a part yet |
It sounds like a cooling fault and it is not. A3 means the drain protection has tripped, so the symptom is water where you do not want it: a stained ceiling, a drip down a wall, or a puddle under the indoor head. The causes are a blocked drain line, a cracked pan, a drain pump that has stopped, or a fall that was never correct from installation. Fixing the blockage without fixing the fall means it comes back next summer.
Freezing detection means the coil has dropped below freezing, and that happens for two reasons. Either not enough air is moving across it, from a blocked filter, a collapsed duct or a failed blower, or the refrigerant charge is low from a leak. Test airflow first because it costs nothing. If airflow is right, pressure test before adding gas.
Do not keep resetting the system to clear a code. Do not add refrigerant because of a C5 code before airflow has been proven good and a leak test has been done. And do not assume a code you found on another brand's chart applies here, because the same letters carry different meanings across manufacturers.
Stop using the unit and call if you can smell burning, if the safety switch trips every time it starts, if water is anywhere near electrical fittings, or if the outdoor unit tries to start and cuts out repeatedly. Everything else can be booked and properly diagnosed.
A3 is abnormal drainage, which means the drain protection has tripped. The symptom is usually water rather than a cooling problem: a drip from the indoor head, a stain on the ceiling or a wet patch under the unit. Common causes are a blocked drain line, a failed drain pump or a fall that was never right.
Possibly, but not necessarily, and you should not assume it. C5 is freezing detection, which happens when airflow across the coil is restricted or when charge is low. A blocked filter or a collapsed duct can cause it. Check airflow first because that costs nothing, then pressure test if airflow is fine.
A0 means an external protection device has activated, which is a shutdown rather than a diagnosis. A1 is specifically an indoor circuit board malfunction. A0 requires tracing the cause at the unit, while A1 points directly at the board, its supply and its connections.
A6 points at an outdoor unit connection issue, which nearly always means the interconnecting cable or its terminations rather than a failed board. It is worth testing the cable continuity and checking for water in a connector before anyone quotes for control boards.
Usually not. A9 is a swing flap motor fault, so the louvres stop moving as they should. It affects comfort and airflow direction rather than the system's ability to cool. It is worth fixing, but it is not urgent and it will not damage the compressor.
No. Manufacturers use different schemes and the same letters mean different things. Use the chart that matches your own model, and check the model number on the indoor unit sticker rather than assuming the outdoor unit is from the same series.
It depends on the fault, the part and how accessible the unit is. Sensor and drain faults sit at the low end, boards and compressors at the high end. We diagnose first and quote in writing before we start, so you know the figure before any work begins.
Reset once to see whether the code returns, because that tells you whether it is a transient event or a real fault. Do not keep doing it. On freezing, pressure and fan faults, repeated restarts can cause further damage and hide the pattern needed for diagnosis.
Yes, regularly. We will also point out anything in the original installation causing repeat faults, such as undersized pipework, a poor drainage fall or a unit that was never properly commissioned, so you are not paying twice for the same problem.
The exact code, the model number from the sticker on the indoor unit, whether the code appears on start or after running, and whether it happens in heating, cooling or both. That usually tells us which half of the system to look at before we attend.
