Cassette rattle traced to loose fan blade clip, not compressor bearing
Aircon case in Dhoby Ghaut, Singapore: noise/vibration traced to fan blade retaining clip had loosened, causing the blade to wobble and rattle against the housing at certain speeds after targeted diagnosis checks.
Case details
What client reported
The aircon in the office started rattling a few weeks ago. It comes and goes depending on the fan speed. Another company inspected it and said the compressor bearings were wearing out and the outdoor unit would need to be replaced.
What we found
We ran the cassette at each fan speed and listened for the rattle before opening anything up.
- Rattle was present at medium fan speed but absent at low and high speeds — this pattern ruled out compressor bearing noise
- Compressor sound was smooth at all indoor fan settings — bearings showed no roughness or grinding
- Opening the cassette panel revealed the fan blade retaining clip had shifted, allowing the blade to wobble at the resonant speed
The retaining clip that holds the fan blade to the motor shaft had loosened over time. At medium speed, the wobble was enough for the blade tip to contact the housing, creating the rattle. At low speed the wobble was too small to make contact, and at high speed the centrifugal force pulled the blade outward past the contact point.
What we did
We re-secured the retaining clip and confirmed the blade sat true on the shaft. The fan was run at all speeds to verify the rattle had stopped. No parts were replaced.
The rattle was gone on the same visit. The compressor and outdoor unit were both fine. The office avoided a full outdoor unit replacement that had been quoted by the other contractor.
Timeline
Day 1
Cassette rattle noticed — another contractor diagnosed compressor bearing failure
Day 5
Ran the fan at each speed setting and isolated the rattle to blade movement, not compressor or bearing vibration
Day 5
Fan blade clip re-secured — rattle eliminated at all speeds
What we learned
Cassette rattle — fan blade vs. compressor bearing.
- A rattle that changes with fan speed usually points to the fan assembly, not the compressor. Compressor bearing noise is steady regardless of indoor fan speed.
- Cassette fan blades sit on a retaining clip. If the clip loosens, the blade wobbles at specific RPMs and contacts the housing.
- Testing at each speed isolates where the noise starts. If the rattle appears only at medium speed but not high or low, the blade is the likely source.
Best next step
If your unit is behaving similarly, start with the service path that fits this case before approving broader scope.
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