Why does my aircon fan keep running after turning off?
A short fan run after shutdown is usually a built-in drying cycle to prevent mould on the coil. But if the fan keeps running far longer than usual, or stops unpredictably, the control path is likely at fault.
By Team Snowflake | Reviewed 30 May 2026
1. Normal post-off drying cycle
You switch the unit off and the fan keeps blowing for a short stretch before stopping by itself. Many units use this post-off run to dry moisture from the evaporator coil. It reduces mold growth while the unit is idle. A short, consistent delay is usually design behavior, not a fault.
How to tell
A drying cycle terminates cleanly every time and is consistently short. Unlike a relay fault, the fan does not run indefinitely or need power cycling to stop. Unlike electrical instability, there are no unusual sounds or odours, and the run-on is designed behaviour.
- Fan stops on its own after a short period.
- No unusual smell or noise during the run-on.
- Next startup is normal.
How we confirm it
We confirm the run-on duration matches the model's built-in drying cycle before treating the pattern as a repair case.
Do not approve a board replacement based on a short post-off run. Check the unit's settings for an auto-dry or self-clean mode first. The behaviour is usually documented in the manual.
2. Sticky fan relay or stop-command path fault
You send the off command and the fan keeps spinning far past the normal drying delay, sometimes needing the isolator to stop it. The indoor PCB fan relay should open on off command. If the contact sticks or welds shut, the fan circuit stays closed.
How to tell
The fan runs far longer than a normal drying cycle, or stops and restarts at random. Unlike a drying delay, the run does not terminate cleanly. Unlike electrical instability, there are no odours or breaker events. When off command response is inconsistent across attempts, the command path is faulty rather than the motor.
- Fan run-on feels much longer than usual.
- Remote off command response is inconsistent.
- Pattern repeats across different attempts.
How we confirm it
We test relay switching response and board output signals to confirm whether the relay is stuck or the board is not sending the stop command.
Do not replace the fan motor before relay switching response is tested. The relay is the cheaper first check, and a sticky contact produces the same surface symptom as a failing motor.
3. Unstable mains disrupting stop sequence
The fan keeps running after off, and there is also a burning smell, breaker trip, or irregular fan speed. Unstable mains power or PCB logic supply can interrupt the off-command sequence. The compressor may stop while the fan relay misses its stop pulse.
How to tell
Physical symptoms alongside the fan run-on are the distinguishing markers: a burning odour near the indoor unit, a breaker trip with operational changes, or the fan running at irregular speeds. Unlike a normal drying delay, the run is not predictable. Unlike a pure relay fault, the issue involves electrical stress on the motor circuit.
- Burning or electrical odour appears.
- Breaker trip appears with operation changes.
- Fan behaviour is erratic with power events.
How we confirm it
Stop repeated on-off testing. We check voltage stability at the board and inspect relay contacts for arcing or heat damage.
Stop using the unit if you smell burning or hear unusual motor sounds. Turn the isolator off and do not attempt further on-off cycling until the electrical fault is assessed.
Related reading
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