What is a Filter drier? A filter drier is important component for maintaining the longevity, efficiency, and safety of an HVAC or refrigeration system by acting as a safeguard against the three main threats: moisture, acid, and particulates. There are three types of filter driers that are used in a system, Liquid Line Filter Drier: The standard type, located after the condenser. Suction Line Filter Drier: Installed after the evaporator and before the compressor. Bi-Flow Filter Drier: Used in heat pump systems where the refrigerant flow reverses direction depending on the mode. Sid Harvey, has you covered with every type of Filter Drier to protect your system.