Because as the ambient temperature changes, may require a different speed "Micro 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 low-speed low-noise in the winter, the use of high-speed summer "Micro Cooling Fan" to get a good heat dissipation. Automatic class radiator thermostat with a temperature sensor in general, can automatically control the fan speed based on the current operating temperature (eg heat sink temperature), high temperatures will increase speed, low temperature, then reduce speed to achieve a dynamic balance, so that "Micro Cooling Fan" cooling effect of wind noise and maintain an optimal combination of points.