These three sentences are all in their simple present tense, because they are statement about the functions of the air conditioner, which is not a temporary or single phenomenon but a fact that will never change. And this can’t be expressed in any other tense.

2.2.3 Use of Passive Voice源'自:751`!论~文'网www.751com.cn

That passive voice is often used in product descriptions or user manuals is because the basic function of a product description is to offer concrete information about the features and usage of the product. It is documented for the product itself and focuses on an objective description, which makes it unnecessary to tell exactly the actor. For example, 

The vent control is located behind the front grille on the right side of the air discharge area. When set at CLOSE, only the air inside the room will be circulated and conditioned. When set at OPEN, some inside air is exhausted outside.

Above is a paragraph in the user’s manual of GE Air Conditioner. All the sentences used passive voice to introduce the vent control, as what is important is the act of operation not the operator.

2.2.4 Use of Elliptical Sentences and Simple Sentences 

Given merely a limited space, and with the purpose of introducing the product objectively and authentically, and teaching consumers how to use the product, user manuals usually uses simple sentences and sometimes even incomplete sentences or sentence fragments. For example, the following is a part of the wicking filter maintenance in the Vicks Humidifier.