Water coming out of a ceiling cassette is one of the most common calls we take, and it is worth understanding because the four realistic causes need completely different work. Guessing wrong means paying for the wrong repair.
1. Blocked condensate drain
This is the cause in most cases. A cassette removes humidity from the air, and that moisture collects in a drain pan and runs away through a pipe. In Dubai the pan stays wet for most of the year, and wet surfaces plus dust produce biological sludge that gradually narrows the drain until it stops.
When the pan overflows, water finds the lowest edge of the unit and drips into the room. Typical signs: it happens after the unit has been running a while rather than immediately, and it worsens on humid days.
The repair is clearing the drain line and cleaning the pan. It is straightforward. What matters is that the pan is actually cleaned rather than just the line blown through, because the sludge that caused it is still sitting there otherwise.
2. Frozen evaporator coil
If airflow across the coil drops far enough, the coil temperature falls below freezing and ice forms. When the unit stops, that ice melts all at once, which is far more water than the drain pan was designed to hold. It overflows.
The tell is timing: dripping starts shortly after switching off, or you find heavy dripping in the morning after overnight running. Look up through the return grille and you may see frost on the coil face.
Airflow restriction has causes of its own: a loaded filter, a fouled coil, a failing blower, or a blower wheel caked with the greasy film that builds up on cassettes over time. Low refrigerant charge from a leak also freezes coils. Fixing the ice without fixing the airflow means it returns within weeks.
3. Condensation on uninsulated pipework
Chilled water pipework and refrigerant lines run above the ceiling. If the insulation has been damaged, compressed by someone working in the void, or was never properly sealed at the joints, the cold surface condenses moisture from the humid air in the ceiling void. That water runs along the pipe and drips wherever it finds an opening, which is often the cassette because that is the nearest gap.
The clue here is that the water appears near the unit rather than out of it, and ceiling staining spreads along the line of the pipe run rather than radiating from the cassette.
4. Failed drain pump
Many cassettes sit lower than the drain they discharge into, so a small condensate pump lifts the water. Pumps fail, and their float switches jam with the same sludge that blocks drains. When the pump stops, the pan fills and overflows.
Some units have a safety switch that shuts the AC off when the pan fills. If yours cuts out rather than drips, that switch is doing its job and the pump is the likely fault.
What to do right now
Switch the unit off and put a container underneath. Running it longer will not clear a blocked drain, and every hour adds to the ceiling repair. Ceiling plaster damage almost always costs more than the AC repair that caused it.
Related: AC leaking water explained, cassette AC systems, coil and filter cleaning.
Need this looked at?
inspection, fixed written price before any work begins, and a before/after photo report on every job.