Cassette Dripping onto Desks: Drain Sludge, Not a Crack

Water reaches the desks below a cassette and a cracked pan is proposed. What to establish before an old unit is talked toward replacement.

By Team Snowflake | Updated 24 Aug 2026

Teaching case based on recurring Snowflake service patterns; identifying details are combined.

How this presents

Desks moved and a bucket underneath, because the indoor unit drips whenever it runs. The unit is old, so replacement has come up alongside the repair. Nothing has been opened or tested yet.

Setup: Daikin Cassette7-9 yearsIndustrialChoa Chu Kang
Misread as: A cracked pan, the cassette lowered from its mount, and an old unit talked toward replacement.
Check first: A cup of water poured into the pan, watched at the outlet

What else produces this

A cup of water poured into the pan settles this before anything is dismantled. If it leaves by the outlet, the drain works and the pan is the suspect. If nothing comes out, the pan is holding water it cannot pass and the overflow is the symptom rather than the fault. It takes a minute and it decides whether a unit comes off the ceiling.

Water poured into the pan producing nothing at the outlet names the blockage immediately.
Water backing up and spilling from the pan's lowest edge is the overflow path, not a breach.
Free drainage the moment the line is cleared, with the overflow stopping at once, closes the question.
A pan surface with no cracks, fractures or corrosion confirms the body was sound throughout.

Why it happens

A cassette drain runs flat for a stretch before it drops, and water moves slowest along that flat section. Sludge, a mix of algae, bacteria and dust, settles wherever water is slow, so the flat run collects it year after year until it closes entirely. The pan then fills and spills at its lowest edge. Nothing about the pan changed. What changed is downstream of it.

What resolution involves

Flush the line under pressure until it runs freely, then pour test water into the pan to confirm drainage is restored rather than merely improved. Nothing comes off the ceiling and no part is replaced. On a unit running long hours the worthwhile change is standing: a drain flush at every service, because the flat run will fill again on the same schedule it filled the first time.

How to tell it worked

Test water poured in after the flush, not just water observed leaving during it. A line cleared under pressure runs while the pressure is on and can still be narrow enough to fill again within weeks.

Before you approve a quote

Over the edge and through the surface are different faults

Ask for a cup of water to be poured into the pan before any unit is lowered. It takes a minute.
A blocked drain overflows the pan's edge. A failed pan wets whatever sits directly beneath it.
Age is not evidence. An old unit with a blocked line has a blocked line, not an old-age problem.

Questions this case answers

Cassette aircon dripping onto desks: is the drain pan cracked?

Rarely, and it is the more expensive assumption. Far more often the pan is intact and the drain below it has closed, so water fills the pan and spills at its lowest edge. The two produce identical puddles and completely different invoices.

How do I know the drain line is blocked before agreeing to lower the unit?

By pouring a cup of water into the pan and watching the outlet. Water leaving means the drain works. Nothing leaving means the line is blocked, and the pan is holding water rather than losing it. That single test decides whether the unit needs to come down.

Why does sludge build up in a ceiling cassette drain?

Because the drain runs flat before it drops, and water moves slowest along a flat run. Anything carried in the water settles where it slows, so the flat section accumulates sludge year after year until it closes.

Does an old cassette leaking water mean it should be replaced?

Not on this evidence. A blocked drain line on an old unit is still a blocked drain line, and the pan here was intact; replacement is a conversation about capacity, efficiency and remaining life, which a puddle on a desk says nothing about.

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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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