A filter drier is a safety device installed in the refrigerant line to remove moisture, acid, and solid contaminants from the system. It contains a desiccant material that "soaks up" any tiny amounts of water that might have entered during the Evacuation process. This is the primary defense for your Compressor, as moisture can lead to internal corrosion and "acid burnout." A new filter drier should be installed every time the refrigeration circuit of an ACIq system is opened for repairs. You will find high-quality driers included in many of our Installation Kits. Because they catch debris, they can eventually become restricted, which is why technicians check the temperature drop across them during service. They are essential for both cooling-only units and Heat Pump Condenser systems that reverse flow. It is one of the most inexpensive parts in the system, yet it performs one of the most critical roles.