Factory cassette dripping again: dust sludge in the drain line
A Pioneer factory office cassette started dripping again after normal servicing. In a dusty industrial building, the question was whether the drain line was carrying sludge from site exposure, not whether the cassette pan or pump had failed.
By Team Snowflake | Reviewed 15 Jun 2026
Case summary
Mitsubishi Electric Cassette9 years oldIndustrialPioneer, Singapore
- Concern
- Facility team worried the cassette pan or drain pump had failed.
- Found
- Industrial dust sludge blocking the cassette drain line
- Key check
- Tested the drain line with water before quoting pan or pump replacement
- Result
- The cassette held a longer test run without dripping. The facility team avoided replacing a working pump and added drain-flow checks to the next service scope. They also had a clearer reporting note for future leaks: whether water appears at startup, after long runtime, or after dusty work nearby. That note helps keep the next quote focused.
What we were told
Water had appeared around the unit edge twice in one month. The office had been serviced, but the drip returned during afternoon runtime. Staff placed a bucket below the unit and asked whether the drain pump or pan needed replacement.
What we checked
We checked the drainage path before quoting parts. In a factory office, dust can load the cassette and drain line even when the visible grille looks acceptable. We inspected the tray, tested water flow, checked ceiling access, and looked for signs that water was backing up instead of leaving the unit.
The cassette pan was intact and held water without leaking from a crack.
Water left slowly when poured into the tray.
Dark sludge returned from the drain line during clearing.
The pump ran, so replacement was not the first answer.
What we found
The cassette was not leaking because the pan had cracked. The drain line was partly choked with dust-heavy sludge, so water collected faster than it could leave during longer afternoon operation. Normal servicing had improved the indoor face, but the line still carried old buildup from the factory environment. Once enough water gathered in the tray, it overflowed at the cassette edge and looked like a unit leak.
What fixed it
We cleared the drain line, flushed the tray, and confirmed water left properly before closing the ceiling panel. The recommendation was to include drain testing in future maintenance, especially after dusty production periods or renovation works nearby. We did not quote pump replacement because the pump operated and the leak stopped after the blocked line was cleared. The site needed a drainage-focused maintenance step, not a part swap.
Outcome
The cassette held a longer test run without dripping. The facility team avoided replacing a working pump and added drain-flow checks to the next service scope. They also had a clearer reporting note for future leaks: whether water appears at startup, after long runtime, or after dusty work nearby. That note helps keep the next quote focused.
What this case teaches us
Factory cassette leaks need the drain line tested
- Industrial dust can turn into heavy sludge once it mixes with condensate. A cassette can look clean at the grille while the drain line stays restricted.
- Ask for a drain-flow test before approving pan or pump replacement. The test should show whether water leaves the unit properly.
- In factory offices, the cleaning scope should match site exposure. Drain checks may need to be more frequent than in a normal office.
Related reading
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