Aircon evaporator coil

The evaporator coil sits inside the indoor unit. Refrigerant flows through it at low pressure, making the coil surface cold. Your indoor fan blows room air across this surface. Heat transfers from the air into the refrigerant, and the cooled air is pushed back into the room.

The coil also removes humidity. As warm air passes over the cold coil surface, moisture condenses and drips into the drain pan below. In Singapore's humidity, this is a significant part of what makes the room feel comfortable.

When the coil is dirty, airflow through it is restricted. The heat transfer drops, cooling weakens, and the drain can overflow from ice melt if the coil gets cold enough to freeze.

Weak cooling that does not improve after a general service is the clearest sign of a coil problem. The filter is clean, the fan runs, but the room still does not cool the way it used to.

Ice on the indoor unit or the connecting pipe signals a blocked coil or low refrigerant. When airflow drops, the coil surface gets too cold and moisture freezes on it.

Water leaking from the indoor unit can also point to the coil — from ice melt, or a coil that is misaligned or cracked.

We start by confirming filter condition and fan speed. If either is compromised, we address those first. Coil assessment only makes sense after airflow is confirmed to be healthy.

We inspect the coil surface visually — looking for bio-film, mould, compacted dust, or physical damage. A coil that responds to general servicing does not need a chemical wash. One with deep-set contamination does.

We also check refrigerant pressure to rule out low gas as the cause of icing. A coil with normal pressure that is still icing has a buildup problem, not a refrigerant problem.

Physical damage — bent fins, corrosion, or a refrigerant leak at the coil — requires replacement assessment. Cleaning a damaged coil does not restore its performance.

Most coil problems are buildup — resolved by chemical wash when general servicing is not enough. Physical damage requiring replacement is less common but does occur on older units or those in harsh environments.

If the unit cools adequately and a recent service included coil cleaning, monitoring through the next service cycle is reasonable. Buildup takes time to reach a level that affects performance.

If ice has formed on the unit, turn it off and let it defrost before running again. Running a unit with a frozen coil stresses the compressor and can cause water overflow. Contact us before restarting.

If cooling is borderline and no ice is present, schedule a service with coil inspection. We will give a clear recommendation — clean, chemical wash, or replace.

The signal is weak cooling that persists after filter is cleaned and coil appears visually clear.

Heavy contamination deep inside the coil reduces heat transfer even if the surface looks acceptable.

Chemical wash is required when visual inspection shows visible particles in the coil material.

When cooling remains weak after filter service and visual inspection, chemical washing is needed.

Coil cleaning — chemical wash — requires partial disassembly of the indoor unit. The cleaning agent dissolves bio-film and compacted dust from inside the fin structure, which wiping cannot reach. It takes longer than a general service but is not a major job.

Coil replacement is a significant repair. The coil is a core component of the indoor unit and replacement requires sourcing a part specific to the model. On older units, the coil may no longer be available separately from the full indoor unit assembly.

If a technician recommends a chemical wash and cooling does not improve after it, the coil condition or refrigerant needs to be reassessed. A wash that does not improve performance means the cause was not buildup.