Cassette uneven airflow traced to one-sided blower wheel buildup

What we found

The split airflow pattern pointed to something physical inside the blower path rather than a motor or damper fault. The panel was removed for a direct look at the blower wheel.

• 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

Dust and debris had compacted heavily on one side of the blower wheel over the years. The caked section could not move air effectively, so the vanes on that side had reduced airflow. The clean side continued pushing air normally, creating a lopsided distribution pattern.

What we did

The motor and dampers are both functioning normally. A chemical clean of the blower wheel will remove the compacted buildup and restore even airflow across all four vanes. No parts need replacing.

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.

What we learned

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 than the other.
• 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.
• 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.