Can dust buildup cause weak airflow even if the fan is spinning?

Yes. Buildup on the fan barrel and evaporator coil adds weight and restricts air movement. The fan can spin normally and still deliver poor airflow if the blades are coated or the coil is blocked.

How do you tell if it's the motor or buildup causing weak airflow?

We check motor behaviour during operation and test for resistance during manual rotation. If the motor runs freely and shows normal operation, buildup is the likely cause. The fan barrel is then inspected directly.

Does cleaning the filter prevent this from happening?

Filter cleaning reduces buildup but doesn't eliminate it. Fine particles pass through the filter over time and settle on the coil and fan barrel. A chemical overhaul reaches these areas and removes what filter cleaning cannot.

Cold But Weak Airflow

A client was told to replace their fan motor due to weak airflow. We checked the unit and found a much simpler, cheaper cause. Before replacing major parts, always get a second opinion.

Case Details

LocationBishan, Singapore

BrandMitsubishi Electric

Unit age4 yrs

ComplaintThe air is cold but the airflow has been getting progressively weaker each week, even though the fan is visibly spinning. The unit was serviced several months ago and the filter was cleaned then.

CauseHeavy dust and lint buildup on fan barrel and evaporator coil

The Assessment

Weak airflow with a spinning fan rarely means motor failure. Motors tend to fail completely, not gradually. We checked for blockages first, then tested the motor.

Opened indoor unit: fan blades coated in thick dust and lint despite a recently cleaned filter
Dust buildup behind the filter on the evaporator coil and fan barrel
Motor behaviour looked normal during operation
No signs of bearing drag during manual rotation

The Diagnosis

The filter catches most dust, but fine particles still get through. Over time they build up on the coil fins and fan blades. This adds weight to the fan and restricts airflow. The motor was working normally — but the system was clogged. Cleaning the filter doesn't remove this deep buildup. It needs a full chemical wash.

Do a chemical overhaul — disassemble the indoor unit, remove buildup from the fan barrel and evaporator coil, and reassemble. If airflow is still weak after cleaning, test motor performance then. Cleaning first is the logical step before replacing a motor that is still running.

The Outcome

Client chose the chemical wash. We removed significant buildup from the fan barrel and coil fins. After reassembly and test run, airflow returned to normal strength. Temperature drop measured correctly. The original motor is still running fine.

Timeline

Several months agoClient noticed airflow getting gradually weaker

A few months agoAirflow noticeably reduced — contacted previous contractor

Same weekContractor recommended fan motor replacement

Following weekClient contacted Snowflake for second opinion

Following week (same visit)Snowflake assessment: Motor running fine, heavy dust buildup on fan barrel and coil

Same visitChemical overhaul completed — airflow restored to normal

PresentAirflow strong, original motor still intact

What This Means for You

Does this sound familiar?

Fan is spinning normally but air feels weak
Room takes much longer to cool down than usual
Aircon was serviced recently but only the filters were washed

If yes, your cooling coil or blower wheel is likely choked deep inside. A standard wash won't reach it — you need a chemical overhaul to restore airflow.

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