Diagnosis
The unit is in Smart Mode. The fan speed is automatically adjusting based on readings from its internal particle sensor.
How to Fix It
Exit Smart Mode. Press the Fan Speed button on the control panel or remote until the LED indicator is on a specific number (1, 2, or 3). The word 'Auto' or 'Smart' on the display will disappear. The fan will now remain at your manually selected speed.
If That Didn't Work
Check for a scheduled timer. Press the Timer button to cycle through settings. Ensure no timer is active (display should show '--'). An active timer can trigger a pre-set fan speed change.
Heads Up
In Smart Mode, a temporary spike in particles (like cooking smoke or dust) will cause a sudden, loud shift to high speed. This is normal operation. If you prefer constant noise levels, manual speed selection is required.