Because as the ambient temperature changes, and sometimes need different speeds "220V Cooling Fan" to meet demand. Some manufacturers specially designed heat sink can adjust the fan speed, manual and automatic modes. Manual is designed to allow users to use a low speed in the winter low-noise, high speed to get good cooling effect during the summer. Automatic Class thermostat "220V Cooling Fan" radiator with a thermostat sensor generally can automatically control the fan speed based on the current operating temperature (eg heat sink temperature), the temperature is raised high speed, low temperature, then reduce speed in order to achieve a dynamic equilibrium, so that "220V Cooling Fan" cooling effect of wind noise and maintain an optimal combination of points.