Cassette started dripping after routine cleaning: drain trap dried out
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 | Reviewed 3 Mar 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
- Drain trap lost prime after cleaning sequence
- Key check
- Performed a controlled drain flow test and confirmed the trap had no standing water seal
- 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. On a cassette, the drain trap holds a small pool of water that keeps drainage flowing. Empty that pool and water backs up, even when the pipe itself is clear.
Panel and filter were clean, with no ice on the coil.
The drain line was open, with no blockage along the pipe run.
The trap section held no standing water.
During steady operation, water backed up in the tray and spilled at the panel edge.
What we found
The drain trap lost its water during the cleaning. The trap holds a standing pool of water that keeps the drain flowing steadily. The trap was likely emptied during filter removal and not refilled afterward. With the pool gone, water no longer drained at full speed. The coil still produced condensation and the tray still collected it as normal, but the tray filled faster than it could drain. Over several hours of steady cooling, the tray slowly rose until it overflowed at the panel edge. That is why the dripping showed up every afternoon.
What fixed it
We refilled the drain trap by pouring water into the trap section to restore its standing pool. We then ran a flow test to confirm water discharged steadily through the drain 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 pipe work was needed. The fix simply restored the water that the cleaning had emptied.
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, the drain trap holds a small pool of water. Cleaning can empty it, and an empty trap stops draining.
- Tell us the last service date and what was touched. That separates a service slip from a part fault.
Related reading
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