One room warm, other rooms fine: coil buildup, not low gas
When one room stays warm but the others still cool normally, low gas rarely explains it. A shared system loses gas everywhere at once, not in a single room. So the team compared rooms before quoting a top-up.
By Team Snowflake | Reviewed 26 Feb 2026
Case summary
Mitsubishi Heavy Wall-mounted10 years oldCondoQueenstown, Singapore
- Concern
- The owner worried the refrigerant had run low across the system and every indoor unit would need a gas top-up
- Found
- Indoor coil and airflow restriction in the affected room only
- Key check
- Compared room-by-room cooling behavior before treating it as a system-wide refrigerant problem
- Result
- Once the coil and blower in that one unit were cleaned, the master bedroom cooled normally again. No system-wide work, and no gas top-up.
What we were told
The living room and second bedroom cooled fine. The master bedroom stayed warm no matter the temperature setting or fan speed.
What we checked
When one room loses cooling on a shared system, the check starts with comparison, not a guess about gas. The team went unit by unit, measuring airflow, feeling each coil, and looking at the blower to tell whether the fault was isolated or system-wide.
The living room and second bedroom units cooled normally. Good airflow, a cold coil, and the room temperature dropping as expected.
The master bedroom unit pushed noticeably less air, and what came out was barely cool rather than cold.
Opening that unit showed heavy buildup on the evaporator coil. The lower rows were coated with a dust-and-moisture layer that blocks heat exchange.
The blower wheel in the same unit also carried moderate buildup, cutting air volume across the already-clogged coil.
The outdoor unit ran normally and the other rooms cooled well, so the refrigerant was not the problem.
What we found
The master bedroom unit had heavy dust-and-moisture buildup on its evaporator coil, mostly on the lower rows where condensation collects. That coating blocked heat exchange, so the coil could not cool the passing air properly. The blower wheel added a second restriction, pushing less air across the already-clogged coil. A starved coil and weak airflow together left the room much warmer than the rest of the flat. The refrigerant was never the issue. All rooms share one outdoor unit, and the others cooled normally, so a gas top-up would have been wasted money.
What fixed it
No gas work was needed, since the other rooms confirmed the refrigerant was fine. The fault sat only in the master bedroom unit, with a clogged coil and a buildup-laden blower wheel. The team recommended a chemical wash to clear both surfaces, since a standard general service would not shift packed-in buildup. After the wash, every room was retested to confirm the master bedroom matched the others again. They also flagged that this room may need servicing more often, because it runs longer hours and fouls faster.
Outcome
Once the coil and blower in that one unit were cleaned, the master bedroom cooled normally again. No system-wide work, and no gas top-up.
What this case teaches us
One warm room on a shared system points inward, not to the gas
- A shared outdoor unit feeds every room from the same refrigerant. If most rooms still cool, the gas is fine and the fault sits in the warm room's own indoor unit.
- Here the cause was a clogged coil and a dust-coated blower wheel in the master bedroom. Both starve that room of airflow while the rest of the flat cools normally.
- Note which room stays warm before booking work. The room-by-room pattern shows whether the fault is local or system-wide, and can save you a top-up you do not need.
Related reading
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