A-Coils

An a-coil is also called an evaporator coil. The a-coil is the inside part of a split-system air conditioner. Freon pumped from the outside unit cools the a-coil. The furnace's fan motor blows air across the cooled coil and into the home's ductwork. A-coils that fit directly inside a furnace are called uncased coils, and coils that install next to the furnace are called cased coils.
Help Sources:
Cleaning An A-Coil