Aircon Cassette Uneven Flow, Dirty Blower

Case Details

What We Checked

• Motor was running at normal speed and drawing expected current.
• Damper vanes moved freely when tested manually.
• Blower wheel had heavy compacted dust on the side facing the weak vanes.
• Clean side of the wheel corresponded to the strong vanes.

The Diagnosis

Dust and debris had compacted heavily on one side of the blower wheel over fifteen years of continuous commercial use. A cassette blower wheel spins at high speed and flings air outward through all four discharge paths equally — but only when the blade surfaces are uniformly clean. The caked buildup on one side added weight and reduced the effective blade surface area, cutting air volume to those vanes. The clean side continued pushing air at full volume, creating a lopsided distribution pattern that worsened gradually as more dust layered onto the already caked section.

What Fixed It

We confirmed the motor and dampers were both functioning normally — the imbalance was entirely caused by the blower wheel buildup. We recommended a chemical clean of the blower wheel to dissolve and flush the compacted dust from the blade surfaces. No parts needed replacing. We also advised scheduling blower cleans during each chemical wash cycle going forward, given the unit runs in a dusty industrial environment with extended daily operating hours.

After a chemical clean of the blower wheel, airflow became even across all four vanes. Staff under the previously weak side confirmed the difference immediately. No motor or damper replacement was needed.

Why This Happens

Why cassette airflow can become uneven without any part failure.

• Blower wheels in cassette units sit centrally and push air outward to all four vanes. Dust does not always accumulate evenly — one side can cake up heavier depending on where the return air intake draws from and how the surrounding airflow patterns carry particles.
• Compacted buildup on one side of the wheel reduces air volume to those vanes while the clean side continues blowing normally. The result looks like a damper or motor problem, which is why technicians who skip the blower inspection often jump to more expensive diagnoses.
• A chemical clean of the blower wheel restores balance without replacing any parts. In older commercial units, this buildup can go unnoticed for years between deep cleans because the decline is gradual and staff adjust without realising it.
• Ask your technician to measure discharge velocity at each vane before and after servicing. If two sides read significantly lower, the blower wheel is the first thing to inspect — not the motor or damper mechanism.