In the case of CTECHi G240n/G320n, the fan will switch-on on its own once the battery’s core temperature or inverter temperature reaches 60°C (140°F). 2. When the CTECHi GT500 reaches 45°C (113°F), or when the output power reaches 100W, the fan will turn on. 3. If you are using CTECHi GT1200, the fan will automatically start when the battery core temperature or inverter temperature reaches 45°C (113°F) or the output power reaches 100W. If you still haven't found a satisfactory answer, you can submit your queries directly on the product page, drop us an email at Service@ctechipower.comor directly send us a message, and we will get back to you as soon as possible, and we'll be glad to guide you further.