One Side of the Room Always Warmer: Stuck Louver Vane

One side of a room stays warmer than the other all year. Whether that is two faults or one changes the recommendation entirely.

By Team Snowflake | Updated 24 Aug 2026

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

How this presents

One side of a room consistently warmer than the rest, served by a ceiling unit that otherwise performs normally. Air comes strongly from three of its four sides. The imbalance has been present long enough that furniture has been moved to work around it.

Setup: Daikin Cassette10-12 yearsHDBGeylang
Misread as: A failing unit with two separate problems, likely to be worth replacing rather than repairing.
Check first: Watching each vane complete a full sweep from the floor

What else produces this

An outlet delivering nothing at all is different from one delivering weakly, and the distinction directs the whole inspection. Nothing means an obstruction rather than a restriction, and on this type of unit the obvious candidate is the vane itself, which is visible from the floor. Watching each vane through a full sweep takes less time than any measurement and settles which of the four is not participating.

Three sides performing normally place the fault at one outlet rather than anywhere shared.
A vane that does not move through its sweep while the other three do names the obstruction directly.
Heavy fouling on the coil section behind that vane, with the rest of the coil far cleaner, is the second finding.
A long-standing imbalance explains how the fouling had time to build in one quadrant only.

Why it happens

A vane seized in the closed position stops air passing through its section of the coil. Moving air keeps a coil relatively self-cleaning and carries moisture away; still air does neither. The section behind the stuck vane therefore stays damp and collects deposit steadily while the other three stay serviceable. One mechanical fault produces a fouling problem that looks unrelated to it.

What resolution involves

The vane mechanism is freed and the fouled section cleaned, because treating either alone leaves the other. It is worth being blunt about the sequence: fixing the vane without cleaning gives a working outlet blowing through a dirty coil, and cleaning without freeing the vane means the same quadrant fouls again. Order of discovery is not order of importance.

How to tell it worked

All four vanes watched through a complete sweep after the work, and each outlet compared. A mechanism freed by hand can seize again on the motor, which only shows on a full powered cycle.

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Still air fouls the coil behind it

An outlet giving nothing points at an obstruction. One giving a little points at a restriction.
Watch the vanes sweep from the floor. It is the fastest check available and needs no tools.
A mechanical fault left long enough grows a second, dirtier problem behind it.

Questions this case answers

One corner of the room stays warm with a cassette aircon: why?

Because one louver vane has seized closed, so that outlet delivers no air and the corner never gets cooled. The still air also lets the coil section behind the vane foul, which makes the imbalance worse the longer it is left.

Would low gas cause uneven cooling in one part of a room?

No, a refrigerant shortage weakens cooling everywhere at once, so it cannot explain warmth in one corner. Watch the vanes from below through a full cycle: all four should open and close together and travel the same distance, and one that stays put or moves less than the others is the one to look at.

What makes a cassette louver vane seize up?

Dust and moisture settle on the pivot the motor drives, and friction climbs quietly until the motor can no longer swing the blade. Stopping at the vane is the common error: the outlet works again but blows through a fouled section, so that side still underperforms and the fouling continues to build.

How often should a ceiling cassette be serviced?

The interval matters less than the scope: the service has to cover both the vane mechanism and the coil behind it, because fixing one without the other leaves the same imbalance to return. A general clean that skips either one is not enough.

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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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