An accumulator is used in systems that have orifice tube instead o expansion valve. An expansion valve controls the entry of refrigerant into the evaporator. An office tube also does the same thing. It has a very small opening through which liquid refrigerant passes. It is a fixed device with no moving parts. It cannot vary the amount of refrigerant flowing into the evaporator the way an expansion valve does. In case of orifice tubes there always chances of more refrigerant flowing into the evaporator. An accumulator’s primary function is to store liquid refrigerant that is exiting the evaporator, to prevent it from reaching the compressor. Entry of liquid refrigerant into the compressor can damage it. An accumulator is considerably larger than a filter/drier. It is located near the evaporator outlet, in the low-pressure section of the system.