Air should be filtered as soon as possible after it enters the air-conditioner. In the window unit, the air filter is located on the air entering side of the cooling coil. Either permanent or replaceable filters are used. The permanent filter is a metallic mat or plastic foam type. It is coated with odourless mineral oil that helps in catching dust particles. It may be cleaned as needed by washing in soap flakes. Replaceable filters are made of spun glass or similar materials and are also coated with oil or other suitable adhesive. They may be easily removed from the unit and replaced by a new filter.
The air system on the outside includes in the condenser fan and dissipates the heat taken from the cooled area to the outside atmosphere. The air system within the cooled area circulates room air over the cooling unit. These two air systems are so arranged that the cooling coils are located on the room side of the window and condensing units on the outside of the window. It is important that no intermingling of hot condenser air and cooled room air takes place. A partition inside the air conditioner separates the room air from the condenser air. The rubber seals and panels at the window prevent exchanges of inside and outside air. Tight installation at the window is of utmost important.