A3
Daikin Split AC
Severity: ModerateWhat Does This Error Mean?
Daikin A3 means the indoor unit detected an abnormal water level in the drain pan.
Either the drain line is blocked, the drain pump itself stopped working, or the float switch is sensing falsely.
The unit shuts off cooling to prevent the pan from overflowing into your wall.
Most A3 cases trace to a slime-clogged drain line — clearing it solves the problem in under 30 minutes.
Affected Models
- Daikin FTXM ducted indoor units
- Daikin VRV indoor units with drain pump
- Daikin FCQ ceiling cassette
- Daikin FFA cassette
- Daikin Quaternity FTXR
Common Causes
- Drain line clogged with biofilm or algae
- Drain pump impeller jammed
- Drain line installed with insufficient slope (slow drain)
- Float switch dirty and giving false readings
- External drain pipe iced over in winter (heat-pump installs)
- Pump motor failed after years of use
How to Fix It
-
Power off at the breaker.
Switch off the indoor unit breaker.
If the pan is full, do not open it on a powered unit — water and 240V do not mix.
Wait until the unit is fully de-energised. -
Find and clear the drain line.
Trace the small flexible drain hose from the indoor unit.
It usually exits the building through a wall or out the bottom of a cassette.
Disconnect at the unit end.
Run water through with a small bottle or use a wet/dry vacuum at the outside end to suck out slime. -
Vacuum the drain pan.
Open the indoor unit cover (cassette panel down, or wall unit cover up).
The drain pan is the trough under the coil.
Vacuum any water out.
Wipe away algae and biofilm with a damp cloth. -
Inspect the pump and impeller.
On units with a drain pump (cassettes, ducted units), the small pump sits inside.
Listen for it during a heat call — it should hum audibly.
Silent = pump motor failed.
Hum but no flow = impeller jammed by debris or a small piece of insulation. -
Test the float switch.
The float switch sits in the drain pan as a small black or red plastic float.
Lift it gently — the unit should report A3 when lifted, and clear when lowered.
If it is dirty, wipe with a damp cloth.
If it does not move freely, replace it (15-30 USD). -
Verify drain line slope.
The drain hose should slope continuously downward from the unit to its termination.
Any uphill section traps water and slows drainage.
Reroute or shorten the hose so gravity does its work. -
Reset and observe.
Restore power.
Cycle the system to Cool.
Watch for A3 within 30 minutes.
If the alarm clears and stays cleared, the line was the issue.
If A3 returns, the pump itself or its sensor needs replacement.
Frequently Asked Questions
How often should the drain line be cleaned?
In humid climates, once a year.
In drier areas, every 2-3 years.
A small amount of bleach poured down the line during seasonal service stops algae from building back up — pour, wait 15 minutes, flush with water.