Why is my aircon noisier or weaker after servicing?
A unit that came back noisier than it went in was reassembled slightly wrong. Nothing has failed. Something is sitting where it should not, and the fan is now working against it.
By Team Snowflake | Updated 19 Aug 2026
1. Blower wheel refitted off-centre
A soft rubbing or rattling that arrived with the service, together with weaker airflow, usually means the blower wheel went back slightly off its centre. An off-centre wheel brushes the housing at certain points in every rotation. It also moves less air, which is why cooling feels worse at the same time.
How to tell
This path costs you airflow. Unlike a loose panel, cooling has measurably weakened alongside the noise. Unlike a sagging filter, the sound comes from inside the housing rather than from the air path.
- Airflow dropped at the same time the noise appeared.
- The sound is a soft rub or rattle, not a whistle.
- It is there at every fan speed, not just one.
- Everything was fine before the service visit.
How we confirm it
We open the unit and recentre the blower wheel on its shaft. Airflow is then measured after refitting to confirm it has come back to where it was.
A motor replacement is not the fix here. The motor was fine before the service and is fine now, so the new part will sit off-centre in exactly the same housing.
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2. A panel or cover not seated flat
A rattle that appears only at higher fan speeds, with airflow unchanged, usually means a panel did not seat flat after the unit was opened. Ceiling access and cassette panels have to sit square in their frame. A loose edge vibrates against that frame and sounds mechanical from the room below.
How to tell
This path leaves airflow alone. Unlike an off-centre blower, cooling is unchanged and only the noise is new. Unlike a sagging filter, pressing the panel silences it immediately.
- Airflow is exactly as strong as it was before.
- The rattle only shows at higher fan speeds.
- Pressing on the panel edge stops the noise.
- The panel or cover looks slightly proud on one side.
How we confirm it
We reseat the panel square in its frame and check every fixing along the edge. The unit then runs at full speed to confirm nothing vibrates.
Do not let this be quoted as a fan fault. The noise disappears under light finger pressure on the edge, which no failing motor ever does, so no part needs replacing.
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3. Filter not clipped back into place
A flutter or whistle with weaker airflow, soon after a clean, often means a filter retaining clip was not pushed back. Without that clip the filter sags under its own weight, drifts into the air path and flutters as air passes it. Air also bypasses the sagging edge instead of passing through.
How to tell
This path is in the air path rather than the machine. Unlike an off-centre blower, the noise is a flutter of air instead of a rub. Unlike a loose panel, airflow has dropped as well as the unit getting noisier.
- Airflow is weaker and the sound is a flutter or whistle.
- It started within days of the filter being cleaned.
- The filter looks slightly out of line behind the cover.
- The noise changes as the fan speed changes.
How we confirm it
We reseat the filter and engage every retaining clip so it sits flat across the intake. Airflow is then checked to confirm nothing is bypassing the filter edge.
A chemical wash is not the fix for a filter that is simply not clipped in. Paying for a deeper clean misses the clip, so the flutter and the weak airflow both survive it.
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