Cassette airflow getting weaker: corrosion slowing the fan motor
A ceiling cassette in an older Hougang HDB flat was blowing weaker each week, yet still cold. The filters had just been cleaned and looked fine, so the easy answer was already off the table. The fan was being held back by something the owner could not see.
By Team Snowflake | Reviewed 14 Mar 2026
Case summary
Daikin Cassette10 years oldHDBHougang, Singapore
- Concern
- The owner feared the cassette had failed inside and would need a full unit replacement.
- Found
- Corrosion at motor contact points reduced fan power, not a blockage issue
- Key check
- Measured fan motor power under load and found it dropping too low
- Result
- After the corroded contacts were cleaned and protected, motor power returned to normal. Airflow strength came back to its pre-corrosion level, and the fan reached full speed again. The unit has been running at full capacity since, with no parts replaced.
What we were told
Airflow from the ceiling unit had grown noticeably weaker over the past few weeks. The owner had cleaned the filter, but it made no difference. The unit was still producing cold air, just very little of it. That last detail mattered, because a unit that cools but barely blows points to a fan problem rather than a cooling fault.
What we checked
Weak airflow usually starts with the filter, so we confirmed that first. With the filter ruled out, the remaining suspect was the fan motor, so we measured the power reaching it while the unit ran.
The filter was clean and clear, so it could not be choking the airflow.
The motor was spinning, but the fan never reached full speed.
Motor power dropped too low under load, which explained the weak wind.
Visible corrosion sat at the motor wire connection points on the control board.
What we found
Years of heat and humidity inside the ceiling cassette had corroded the motor contact points. A ceiling unit traps warm, damp air around its wiring, and over a decade that slowly eats at exposed metal connections. The corrosion built up a layer of resistance in the power path to the motor. Less power reached the motor than it needed to run at full speed. So the fan slowed even though the unit was calling for full output. The motor was not failing. It was simply being starved at the connection, which is why the symptom crept in gradually rather than failing all at once.
What fixed it
We advised the owner that the motor itself was fine and the corroded connection was the fault. Cleaning the contact points and applying a protective coating would clear the resistance and let full power reach the motor again. That would restore the airflow with no motor replacement and no new unit. Replacing healthy hardware would have cost far more and fixed nothing.
Outcome
After the corroded contacts were cleaned and protected, motor power returned to normal. Airflow strength came back to its pre-corrosion level, and the fan reached full speed again. The unit has been running at full capacity since, with no parts replaced.
What this case teaches us
A weak fan can mean a starved motor, not a dead one
- Clean filters that change nothing rule out the obvious cause. The next thing to check is whether the motor is getting full power.
- Years of heat and humidity inside a ceiling cassette can corrode the wire connections. The motor stays healthy, but corrosion starves it of power.
- Cleaning corroded contacts is far cheaper than swapping a motor or unit. Confirm the motor is genuinely faulty before paying for a replacement.
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