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Error Code
A3 means the unit has found water where it should not be. A float in the drain pan lifts when the water level rises and the system stops to keep the ceiling dry. Fujitsu reports it as abnormal drainage, which covers a blocked line, a frozen section of pipe, or a pump that has stopped lifting condensate away. It is a water fault, not a cooling fault.
Dust, biofilm and algae build up in a drain line over a season and the narrowest point blocks first. Water backs up to the float and A3 trips. Algae is the specific problem in warm weather, because it grows in the standing water inside the pipe. A wet vac on the outlet clears most of them in a few minutes.
Where the drain runs through a cold space or sits against an uninsulated surface, it can freeze in cooling mode. Ice blocks the pipe as effectively as dirt, then melts into a puddle once the unit stops. Insulating the exposed section fixes it, and if the pipe keeps freezing the indoor coil needs checking for a separate airflow problem.
Where the installation has no gravity fall, a small pump lifts the condensate away. Those pumps have a float and an impeller, and both jam with slime or scale over time. You can usually hear whether the pump runs when the unit starts. A silent pump with power at the terminals has failed and is a straightforward swap.
The drain is traced from the indoor pan to its outlet and checked for kinks, low spots where water can sit and any section crushed behind a wall. The outlet is then cleared with a wet vac or low pressure water. Most A3 codes end here, with no parts required and no callout beyond the clean.
A frozen drain is left to thaw fully before anything is pushed through it, because forcing a frozen pipe splits it. Once clear, the exposed run is insulated so it does not refreeze. If ice returns, the cause is usually the indoor coil running too cold, which points at airflow or charge rather than the drain.
On pumped installations the pump is tested on its own: power at the terminals, float moving freely, and water actually lifting away while the unit runs. A pump that hums without moving water has a jammed impeller. One that does nothing has a failed motor or a float stuck down. Both mean replacement.
The manual gives the drain routing, the fall required and the pump specification for that model. Working from it matters on A3 because the required arrangement differs between wall mounted, ducted and cassette units, and a generic fix will not suit all three. It is also where the correct pump part number sits.
