Cassette dripping after cleaning: debris in the drain line

The cassette began dripping from the panel edge the day after routine cleaning. Cooling was still strong, which pointed away from the worst-case faults. The dripping returned every afternoon, always at the same time.

By Team Snowflake | Updated 28 Jul 2026

Case summary

Panasonic Cassette9 years oldOfficeDowntown Core, Singapore

Concern: A cracked indoor coil was the worry, with replacement shutting down the office for days.
Found: Debris knocked into the drain line during the cleaning visit caused a partial blockage and a slow afternoon backup
Key check: Performed a controlled drain flow test and traced a partial blockage further down the pipe run, not at the trap
Result: The afternoon dripping stopped. The tray level held steady through a full day of cooling, and the panel edge stayed dry. No ceiling tiles needed replacement.

What we were told

The unit started dripping the day after routine cleaning. Cooling felt the same as always. By late afternoon, drops kept forming around the panel edge. The office manager was worried about water damage to the ceiling tiles.

What we checked

Cooling was stable and the coil showed no ice. That ruled out a refrigerant problem early, since a starved or iced coil would have cooled poorly. A unit that cools well but still drips has a drainage problem, not a cooling one. So we traced the drain path in order: trap, tray, then the pipe run. Cleaning and panel removal can knock loose debris into the line, and a partial blockage lower down is enough to slow drainage even when the trap and tray look fine.

Panel and filter were clean, with no ice on the coil.
The drain trap held its normal water seal, which ruled out a lost prime as the cause.
Further down the pipe run, a flow test found a partial blockage from debris caught in the line.
During steady operation, water backed up in the tray and spilled at the panel edge.

What we found

A piece of debris was knocked into the drain line during the cleaning visit, most likely dislodged when the filter or panel was removed. It settled inside the pipe run and partially blocked it. Enough of the line stayed open for water to trickle through under light load, but steady afternoon cooling built up condensate faster than the partial blockage could clear. The tray backed up and spilled over the panel edge. The trap itself was intact and did not need attention. The obstruction sat further down the line.

What fixed it

We flushed the drain line to dislodge the debris and confirmed clear flow along the full pipe run. We ran a flow test to check that water discharged steadily through the line under normal cooling. We watched the tray level over a long run to make sure it held steady and did not climb toward overflow. No coil replacement, pump repair, or trap work was needed. The fix simply cleared what the cleaning visit had knocked loose.

Outcome

The afternoon dripping stopped. The tray level held steady through a full day of cooling, and the panel edge stayed dry. No ceiling tiles needed replacement.

What this case teaches us

A drip that starts right after cleaning usually traces to the drain, not the coil

Strong cooling with a new drip points to drainage, not a cracked coil or a failed pump.
On cassettes, cleaning and panel removal can knock debris loose into the drain line. A partial blockage there is enough to cause a slow, steady backup.
Tell us the last service date and what was touched. That separates a service slip from a part fault.

Questions this case answers

Cassette aircon dripping after a cleaning visit: what causes it?

Debris knocked into the drain line during the work, most often when the filter or panel comes off. In this Downtown Core office a piece settled part-way down the pipe run and half-blocked it. Light load trickled through, but steady afternoon cooling made condensate faster than the restriction could pass, so the tray backed up and spilled at the panel edge.

Ceiling cassette dripping water: is the coil cracked?

Strong cooling says otherwise. A cracked or starved coil cools poorly and usually ices, and neither showed here. Cooling was stable and the coil was clear, which moved the search to drainage instead. That distinction matters, because a coil replacement shuts an office down while a drain clearance is a same-visit job.

Why does the dripping only start in the afternoon?

Because that is when the unit works hardest and makes the most condensate. A partial blockage passes water fine at low load, so mornings looked normal. Once cooling ran steadily the tray filled faster than the line could drain and the level climbed to the lip. The daily clock on the drip was itself the clue that the line was restricted.

Do I need a new drain pump if water is coming from the panel edge?

Not before the line itself is flow-tested along its full run. The trap here held its normal water seal and the tray was intact, and flushing the pipe cleared the obstruction and restored steady flow. Nothing was replaced. Where the water appears tells you little; where the flow stops tells you everything.

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Tell us what’s going on. Symptoms, setup, photos, anything we should know. We’ll assess and come back with the right next step.

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