The evaporator is the component that absorbs heat into the refrigeration system. It is a refrigeration coil made of aluminum or copper with aluminum fins attached to the coil of either type to give more surface area for better heat exchange. There are several designs for airflow through the evaporator coil, and for draining the condensate water from the coil, depending on the installation. The different designs are known as the A coil, the slant coil, and the H coil.
The A coil is used for upflow, downflow, and horizontal-flow applications. It consists of two coils with side-by-side circuits that are spread apart at the bottom in the shape of the letter A. In the upflow or downflow applications, the condensate pan is at the bottom of the A pattern. When used for horizontal flow, a pan is placed at the bottom of the coil and the coil is turned on its side. With the two coils in series, the airflow in the A coil is through the core of the coil; it cannot be from the side. When horizontal airflow is required, slant or H coils may be more desirable.