When "220V Cooling Fan" input voltage exceeds the reference voltage, the fan will be turned on, but this condition depends on the ambient temperature. Note: Thermal resistance is dependent on the ambient temperature. At 70 ℃, if the "220V Cooling Fan" input voltage exceeds 1. 9 2V, the output voltage will be switched to + 12V level; when the input voltage is lower than 1.92V, the output voltage will switch back to -12V level. At 50 ℃, if the "220V Cooling Fan" input voltage exceeds 3. 9 2V, the output voltage will be switched to + 12V level; when the input voltage is lower than 3.92V, the output voltage will switch back to -12V level.