One Room Stopped Cooling in a System-3: Not a Gas Problem
Aircon case in Sembawang, Singapore: airflow traced to evaporator coil and blower wheel heavily fouled in affected indoor unit only — airflow restricted to near zero after targeted diagnosis checks.
Case Details
| Unit | DaikinWall-mounted |
|---|---|
| Age | 5 years old |
| Location | HDBSembawang, Singapore |
| Reported | The client said the master bedroom had been getting progressively warmer over the past month. The living room and second bedroom remained cold. No error codes showed on any unit. They had read that low gas could affect one zone and wanted it topped up. |
What We Checked
- Living room and second bedroom indoor units tested — both producing cold air at normal airflow. This confirmed the outdoor unit and shared refrigerant circuit were functioning correctly.
- Affected bedroom indoor unit checked — blower motor running but airflow at the vents was barely perceptible.
- Evaporator coil inspected after removing the front panel — coil face heavily blocked with compressed dust and visible mould across the fin surface.
- Blower wheel removed — heavy dust had reduced the effective blade area. Airflow was poor despite the motor running normally.
The Diagnosis
The affected bedroom's indoor unit had accumulated heavy fouling on both the evaporator coil and blower wheel. The other two units had not reached this level. The bedroom was used primarily with the door closed, which limited air circulation and increased moisture retention around the coil. It had also been serviced less recently than the other two units — the client had staggered services rather than cleaning all three together. Reduced air movement, higher local humidity, and a longer gap since the last cleaning allowed dust and mould to compress on the coil face and blower blades. Airflow was severely restricted despite the motor running normally.
What Fixed It
A thorough chemical wash of the affected indoor unit's evaporator coil and blower wheel was performed on-site. Cleaning solution dissolved the compressed dust and mould buildup, then everything was flushed out completely. After cleaning, airflow from the bedroom unit matched the output of the other two zones. Refrigerant pressures were checked as a final step — both high-side and low-side readings fell within normal range, confirming the shared refrigerant circuit had never been the issue. No gas was lost and no top-up was needed.
The bedroom cooled normally after the cleaning — no parts were needed and the refrigerant system was not touched. The client was advised to service all three indoor units on the same schedule to prevent one unit from falling behind the others.
Why This Happens
Why one room in a system-3 can stop cooling while others are fine.
- In a multi-split system, all indoor units share the same outdoor unit and refrigerant circuit. But each indoor unit has its own coil and blower wheel that can foul independently.
- A refrigerant or outdoor unit fault affects all indoor units at once. The shared circuit cannot selectively deprive one zone. If two zones cool normally, the refrigerant circuit is not the problem.
- Each room's usage pattern is different. A bedroom with the door closed and little ventilation will accumulate coil and blower fouling faster than a regularly aired living room.
- When one zone in a multi-split fails, check that indoor unit's airflow, coil, and blower first. Do this before checking the outdoor unit or refrigerant pressures.
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