The indoor unit is a key component of a modern air conditioning system. It is the part of the system that is located inside the building, and it is responsible for cooling the air inside the building. The indoor unit is typically composed of an evaporator coil, a fan, and a filter. The evaporator coil is the part of the system that absorbs heat from the air inside the building and transfers it to the refrigerant, which is then circulated outside the building. The fan then circulates the cooled air throughout the building. The filter helps to remove any dust, dirt, and other contaminants from the air before it is circulated. The indoor unit is a critical part of the air conditioning system, as it helps to keep the air inside the building cool and comfortable.