Did You Know Filter-Driers are used to clean and dry the refrigerant before it enters the restriction device and all other components in line with the refrigerant circuit?

This is performed by the flow of refrigerant through a desiccant to filter out moisture, acids, wax and sludge that is introduced at the time of manufacturing, piping or poor refrigeration practices. After the refrigerant passes through the desiccant, it enters a fibrous polyester pad to catch any foreign material that may have bypassed the desiccant. Last there is a 100 mesh screen to support the internal assembly. All of which is contained inside a steel capsule with tubing connection on each end.

There are two main types of filter-driers used in our industries, liquid and suction. Liquid line driers come in two types: directional and bi-directional. With directional, the refrigerant can only flow in one direction and bi-directional are used on heat pumps where the refrigerant will change direction in the liquid line. The filter-drier should never be placed in the discharge line of the unit. There is a component that can resemble the filter-drier. This is a discharge muffler and the shape and physical size comes very close to the filter-drier. When the filter-drier is in the discharge line, there is high risk that the internal desiccant portion of the drier can break apart from the pulsation of the compressor or damage at the time of installation. The desiccant granules will flow with the refrigerant and plug the restriction device and coils. This results in a blockage or large pressure drop of refrigerant. Also desiccant in the drier will not perform to reduce the moisture in the system because of the high temperature of the discharge gases. 

The desiccant is a substance with very hygroscopic properties, meaning it will soak up water vapor from the air or refrigerant surrounding it. There are several different types of desiccants that are used in filter-driers. What application the filter-drier is used for will determine which formula desiccant is used. The refrigerant systems require filter-dries to be used on refrigerant systems that are newly installed, have a high content of moisture, wax and slug, or a system that is a burn-out from a large content of acid. For systems that have experienced a burn-out from acid, they will have a desiccant mixed with a charcoal material to perform and clean up of the system.

The installation of filter-driers has rules that need to be followed. If a filter-drier is not bi-directional, it means the flow of refrigerant is in one direction only. Placing the drier in the wrong direction can cause the desiccant to break apart and travel into other areas of the system, causing harm and failure to the components. In the liquid line, care must be given if the filter-drier can be isolated with isolation valves. Dangerous hydraulic pressures can occur when the valves are closed trapping the liquid refrigerant in that portion of the system. This can result in personal injury. Also, the filter-drier caps should not be removed until it is ready to be installed in the system. With the caps off or if the piping is open for long period of time, moisture will enter the filter-drier reducing its capacity and contaminating the system. Once a filter-drier collects moisture, it cannot be removed by a vacuum pump or heating it. The desiccants used in the driers are a onetime use and are assembled in very dry and controlled environments. 

The filter-drier needs to be checked at the time of preventive maintenance. If the drier has more than a two degree drop of temperature across it, there is an internal restriction and must be replaced. Filter-driers are very important to the operation of the refrigeration systems. With care to the system and operation of these components, it will help with the longevity and continuous operation of the equipment.