Aircon Cassette Warm, Clogged Filter Found

Aircon case in Bras Basah, Singapore: cooling loss traced to filters completely blocked with dust after over a year without cleaning, severely restricting airflow across the evaporator coil after targeted diagnosis checks.

Case Details

Reported: The office unit has been blowing warm air for the past few days. A maintenance company told us the gas had leaked and the system needed a full recharge. The unit is about ten years old and the tenant could not remember the last time the filters were cleaned.
Unit: Daikin · Cassette · 10 years old
Location: Office · Bras Basah, Singapore

What We Checked

All four cassette filters were completely impacted with a thick layer of dust — no visible gaps in the filter mesh.
Airflow from the unit was noticeably weak, with air barely reaching the occupied area of the office.
After removing and washing the filters, airflow returned to full strength across all four vents.
Cooling output returned to the correct temperature range immediately — gas pressure readings confirmed normal refrigerant levels.

The Diagnosis

The filters had not been cleaned for well over a year. Dust had built up until the mesh was almost entirely blocked. With no airflow through the evaporator coil, heat exchange could not occur — the coil was cold but the air in the room was not being cooled. The refrigerant system was fully charged and operating normally throughout.

What Fixed It

Cleaning the filters restored full cooling immediately. No gas recharge or leak repair was needed. The tenant was advised to clean the cassette filters on a regular schedule and shown how to remove the filter panels for washing.

Full cooling was restored after the filter cleaning. Gas levels were confirmed normal. No refrigerant work was performed and no parts were replaced.

Why This Happens

Why filter neglect looks like a gas leak.

When cassette filters are completely blocked, air cannot flow through the evaporator coil. The coil gets cold but the room stays warm because the heat is not being transferred. The output air feels lukewarm — exactly like a low-gas symptom.
Checking the filters is the first and simplest step before testing gas levels. If the filters are visibly blocked and cleaning them restores cooling, the gas was never the issue.
Office cassette units accumulate dust faster than residential units due to foot traffic, paper dust, and longer operating hours. Filters in commercial settings need to be cleaned more frequently than in a typical flat.

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