Cassette Airflow Getting Weaker: Corrosion Slowing The Fan Motor
Weak airflow from a cassette unit on the west-facing side of an older HDB building. Filters had been cleaned recently and looked fine. Something else was slowing the fan down.
Case Details
| Unit | DaikinCassette |
|---|---|
| Age | 10 years old |
| Location | HDBHougang, Singapore |
| Reported | Airflow from the ceiling unit noticeably weaker over the past few weeks. Filter had been cleaned but it made no difference. Unit still producing cold air, just very little of it. |
Diagnostic Turning Point
- Concern: Worry was that the cassette had failed internally and would need full unit replacement
- Key check: Measured fan motor voltage under load and found it dropping below spec
What We Checked
Weak airflow often looks like a filter problem, so we started with a voltage check to confirm the motor was getting full power.
- Filter was clean. Confirmed not the cause.
- Motor voltage under load was 15% below specification.
- Visible corrosion at the motor terminal connection points on the PCB.
The Diagnosis
Years of heat and humidity inside the ceiling cassette had corroded the motor contact points. That corrosion added resistance in the voltage path to the motor. The motor received less power than it needed at full speed, so the fan slowed even though the unit was calling for full output.
What Fixed It
The motor itself is fine, the corroded connection is the problem. Cleaning the contact points, applying a protective coating, and confirming voltage returns to spec will restore the airflow without any motor replacement.
After the corroded contacts were cleaned and protected, motor voltage returned to normal and airflow strength came back to pre-corrosion levels. The unit has been running at full capacity since.
Why This Happens
Weak airflow is not always a blocked path.
- A cassette with a clean filter that still pushes weak air often has a voltage drop at the motor, not a blockage downstream.
- Corroded contact points at the motor reduce the voltage it receives, slowing the fan even when the filter is clear.
- Testing motor voltage under load is the fastest way to rule out a blockage and find the actual cause.
Related Reading
Ready to Get Started?
Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.