preheat fan

例句：

1. 1.Before starting the engine, it's important to preheat the fan.
   启动发动机之前，重要的是要预热风扇。
2. 2.The fan is designed to preheat the air before it is blown out.
   这个风扇的设计是先吹出空气，然后再进行冷却。
3. 3. During the winter months, I like to preheat my car's air conditioning fan before leaving the house.
   在冬天，我喜欢在离开家前预热汽车的空调风扇。