Aircon Fan Keeps 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 runs for fifteen minutes or longer, or stops unpredictably, the control path is likely at fault.
Why this happens
A quick summary of the most likely causes and what to look out for.
| Possible cause | What happens | Severity |
|---|---|---|
| Normal Post-Off Fan Delay | Some units use a short fan delay after off as normal behavior. | Simple fix |
| Control Relay or Command Path Fault | Control relay or board logic faults can keep fan running too long. | Needs assessment |
| Electrical Instability Affecting Stop Behavior | Electrical stress can cause unstable stop commands. | Stop using — call now |
1. Normal Post-Off Fan Delay
Many systems keep the indoor fan running briefly after off to dry moisture from the evaporator coil and prevent mould growth.
Signs to look for
- Fan stops on its own after a short period.
- No unusual smell or noise.
- Next startup is normal.
How to tell this is the cause
What separates this from faults is a short and repeatable run-on period with stable next startup.
What the repair involves
We confirm the run-on duration matches the model's built-in drying cycle before treating the pattern as a repair case.
Normal delay should not be misread as immediate board failure.
2. Control Relay or Command Path Fault
When stop commands do not complete correctly, the fan continues much longer than normal — and the pattern may be inconsistent across attempts.
Signs to look for
- Fan run-on feels much longer than usual.
- Remote off command response is inconsistent.
- Pattern repeats across different attempts.
How to tell this is the cause
What separates this from normal delay is long run-on or random repeat after command off.
What the repair involves
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.
Approving parts before confirming the command path misses simple control issues.
3. Electrical Instability Affecting Stop Behavior
Power instability or stressed components cause erratic fan stop behavior — often with safety signs.
Signs to look for
- Burning or electrical odor appears.
- Breaker trip appears with operation changes.
- Fan behavior is erratic with power events.
How to tell this is the cause
What separates this from logic-only faults is fan run-on with trip, odor, or irregular power behavior.
What the repair involves
Stop repeated on-off testing. We check voltage stability at the board and inspect relay contacts for arcing or heat damage.
Repeated command cycling under unstable power worsens the fault path.
Not Always a Fault
Some brands include a built-in drying delay after shutdown — it feels unusual if you are not expecting it.
How to tell this is the cause
- Run-on duration is consistent each time.
- No trips, odors, or unusual noise.
- Cooling performance stays normal.
If this pattern keeps worsening, move to diagnosis early.
Help Us Diagnose Faster
Just observe, no disassembly required:
What to check before calling
| Check | Look for |
|---|---|
| Run-on duration | short and consistent / long / varies each time |
| Remote response | normal / delayed / inconsistent |
| Next startup | normal / slow / abnormal |
| Safety signs | none / odor / trip |
Cases like this
Related Reading
Guides, troubleshooting, and diagnostic case studies to help you make informed decisions.
Same situation with your aircon?
Tell us the symptom and the unit type. We’ll help you figure out what’s going on.
WhatsApp us