Office cassette not cooling traced to neglected filter, not low gas
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
What client 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.
What we found
Before testing gas levels, we removed the cassette panel and inspected the filters. In a commercial unit that has not been serviced recently, filter condition is the most likely cause of reduced cooling.
- 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 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 we did
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.
Timeline
Day 1
Office cassette blowing warm air — told gas had leaked and needed full recharge
Day 1
Removed and inspected the cassette filters before testing refrigerant levels — filters were visibly impacted with dust
Day 1
Filters cleaned, airflow restored — full cooling confirmed with normal gas levels
What we learned
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.
- 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.
- 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.
Best next step
If your unit is behaving similarly, start with the service path that fits this case before approving broader scope.
Common questions
Same situation with your aircon?
Describe it on WhatsApp