Aircon Chemical Wash Needed After Service

Case Details

What We Checked

• Filter clean — consistent with a client who services on schedule.
• Blower wheel clean — no significant buildup.
• Coil front face looked clean at a quick visual check — this is what previous technicians had seen.
• Coil checked in depth with a torch through the fin channels — compressed scale and dark biofilm visible from about 8mm depth inward, across most of the coil face.

The Diagnosis

The evaporator coil had accumulated deep-seated scale and biofilm inside the fin channels that regular brush-cleaning could not reach. At each general service, the front face of the coil was brushed clean, which made the coil look fine on a quick visual inspection. But behind the first few millimeters of fin depth, mineral scale from condensate water and dark biofilm from biological growth in the constantly wet environment had been compressing over the years. This fouling reduced the effective heat transfer area of the coil progressively, causing cooling output to decline even though the filter and blower stayed clean. The pattern is common in high-humidity environments like Singapore bedrooms with limited ventilation.

What Fixed It

A full chemical wash was performed on-site. Cleaning solution was applied through the fin channels under controlled pressure, left to dwell for the specified duration to dissolve scale and biofilm, then flushed out thoroughly. The drain pan and drain pipe were also cleared to ensure the dissolved material exited the system completely. After the wash, the fin channels were visibly open when checked with a torch. The unit was run and supply air temperature measured at the vent — it had dropped by 4°C compared to before the wash, confirming that heat transfer had been significantly restored.

Cooling was restored to a level the client had not seen for two years. The client was advised to alternate general service and chemical wash going forward. A chemical wash every 12 to 18 months, in addition to the six-monthly general service, will stop this level of deep fouling from returning.

Why This Happens

When regular servicing isn't enough.

• A general service cleans the filter and brushes the front face of the evaporator coil. It removes surface dust collected since the last visit. Nothing more.
• Scale and biofilm build up deep inside the coil fin channels over years. A brush cannot reach them. They form from minerals in condensate water and from biological growth in the wet coil environment.
• When deep coil fouling is present, heat transfer drops steadily. The filter may look clean and the unit may seem normal from outside, but cooling still declines.
• Chemical wash applies cleaning solution under pressure to the fin channels. This dissolves scale and biofilm that the brush-clean cannot reach. It restores the heat transfer surface.