Cassette cooling uneven, louver vane and airflow path at fault

What we found

We opened the cassette panel and checked each vane and coil section before looking at the refrigerant system.

• Three of four louver vanes moved freely — normal operation
• One vane on the warm-corner side was seized near-closed — the motor was running but the linkage had locked up
• Coil section behind the stuck vane had visible scale and dust not seen on the other three sections
• Refrigerant pressures checked — both sides within normal range, charge correct

The vane pivot had seized from dust and moisture on the linkage. With the vane stuck near-closed, airflow through that quarter dropped sharply. The reduced airflow let fouling build up on that coil section over time.

What we did

The linkage was cleaned and freed, then lubricated. All four vanes were confirmed to move freely. The coil section was cleaned. Airflow balanced across all four quadrants within minutes of restart.

Even cooling was restored on the same visit. No parts were needed. The customer was advised to service the cassette every six months. Cassette units sit in sealed ceiling voids and foul faster than wall-mounted units.

What we learned

Cassette uneven cooling — vane fault vs. system fault.

• A cassette unit has four directional vanes. If one is stuck, that quarter of the room gets poor airflow. The other three quarters still cool fine.
• From outside this looks like a refrigerant or capacity fault. But gas faults affect the whole unit equally — not just one corner.
• Checking each vane takes a few minutes. A stuck vane can be seen and felt by hand. Always check this before assuming a system fault.
• A stuck vane also causes localised coil fouling. Less airflow means dust and moisture sit on that section of the coil instead of being blown clear.