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 | Updated 28 Jul 2026

Case summary

Mitsubishi Heavy Industries Wall-mounted10 years oldCondoQueenstown, Singapore

Concern: Refrigerant seemed to have run low across the system, with every indoor unit due 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.

Questions this case answers

Only one room is not cooling but the rest are fine: is it low gas?

Very unlikely on a shared system. All the indoor units draw refrigerant from the same outdoor unit, so a genuine shortage would weaken every room at once. In this Queenstown condo the living room and second bedroom cooled normally while the master bedroom stayed warm, which put the fault inside that one indoor unit.

What makes a single indoor unit lose cooling?

Usually its own airflow. The master bedroom unit here pushed noticeably less air, and opening it showed heavy dust-and-moisture buildup across the lower coil rows plus a coated blower wheel. A blocked coil cannot transfer heat and a coated wheel cannot move air, so the two together left the room far warmer than the rest of the flat.

Can I avoid paying for a gas top-up I do not need?

Note which rooms cool and which do not before booking anything. That room-by-room pattern is free evidence and it settles the question quickly. Here the rooms that still cooled proved the refrigerant was fine, so the visit went straight to a chemical wash of one unit. No gas was added and no system-wide work was quoted.

Why does one bedroom aircon foul faster than the others?

Runtime. A room used through the night runs longer hours than the rest, so more air, dust and moisture pass across its coil. That unit reaches the point where buildup blocks heat exchange sooner than its neighbours. The advice after this repair was to service that room more often rather than put every unit on one schedule.

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