There can be several reasons why a fan might fluctuate in speed by itself. Here are a few possible explanations:
Power supply fluctuations: If the power supply to the fan is not stable, it can result in fluctuations in the fan's speed. This can happen due to issues with the electrical outlet, wiring problems, or fluctuations in the overall power grid.
Fan settings: Some fans have multiple speed settings, including automatic or oscillating modes. If your fan is set to one of these modes, it is designed to vary its speed or direction periodically. Make sure to check the fan's settings and switch it to a constant speed mode if desired.
Mechanical issues: Internal mechanical problems or malfunctions within the fan can cause speed fluctuations. This can include issues with the motor, bearings, or other components. If the fan is old, worn out, or damaged, it might not operate smoothly and could experience speed variations.
Environmental factors: Environmental conditions such as temperature and humidity can affect the speed of certain types of fans. For example, some fans have built-in thermostats that adjust the speed based on the ambient temperature. Additionally, if the fan blades are obstructed by dust, debris, or other objects, it can lead to speed fluctuations.
Interference: In some cases, external interference from nearby electronic devices or radio frequency signals can disrupt the fan's speed control system, causing it to fluctuate. Try moving the fan to a different location to see if the issue persists.
If you're experiencing consistent and significant fluctuations in the fan's speed that cannot be explained by any of the above reasons, it might be worth contacting the manufacturer or seeking professional assistance to diagnose and fix the problem.