Filter driers are devices used in a HVAC system that are a combination of filter and dryer (or drier). A filter is used to remove any particle such as dirt, metal or chips from entering the refrigerant flow control. The refrigerant flow control device could be thermostatic expansion valve or simply a capillary tube.

The filter is sometimes also referred to as a strainer. It is critical that these particles are filtered out and prevented from going into the metering device. It can cause blockage to the passage flow of the refrigerant in the expansion valve and cause improper operation to the system.

A drier as its name imply is used to remove the moisture from the refrigerant. Sometimes it is also referred to as dehydrator or dryer. It is necessary to remove moisture from the system otherwise it may freeze inside the tube causing the flow of refrigerant to be restricted. The moisture will also cause the formation of acids and sludge when in contact with oil in the system.

These devices are usually used in bigger system where the refrigerant circuit is designed for field service. Residential units that are charged with refrigerant at factory level and hermetically sealed do not use these devices as the possibility of moisture and particles entering the system is minimal.

Types of Filter

There are basically two types in used today.

  • Liquid Line Type
  • Suction Line Type

Liquid Line Type is placed after the condenser coil and before the expansion valve. The liquid refrigerant that flows from the condenser to the expansion valve is filtered from particles and moisture before entering it. Good filter will filter out particles that are 20 micron or above from the system.

Some higher end device has sight glass that enables the technician to look into it to see the level of refrigerant. Some have chemical in it that indicate the amount of moisture in the system based on the color of it.

The Emerson EK-164 liquid line drier shown below is able to remove moisture and acid from the liquid refrigerant. It can also remove particles that are bigger than 20 micron from the refrigerant system.

It has a maximum operating pressure of 680 psig and painted with a corrosive resistance epoxy powder paint. Suitable for outdoor installation.

Emerson EK-164 liquid line filter driers being installed on site.

Suction Line Type is placed after the evaporator and before the compressor. This device is used to protect the compressor especially after any failure that contaminates the system.

Motor failure in the compressor usually cause acid and other contaminants to be introduced into the refrigerant system hence it is important to have the suction line filter dryer installed.

Editorial Contributors
Alora Bopray

Alora Bopray

Staff Writer

Alora Bopray is a digital content producer for the home warranty, HVAC, and plumbing categories at Today's Homeowner. She earned her bachelor's degree in psychology from the University of St. Scholastica and her master's degree from the University of Denver. Before becoming a writer for Today's Homeowner, Alora wrote as a freelance writer for dozens of home improvement clients and informed homeowners about the solar industry as a writer for EcoWatch. When she's not writing, Alora can be found planning her next DIY home improvement project or plotting her next novel.

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Roxanne Downer


Roxanne Downer is a commerce editor at Today’s Homeowner, where she tackles everything from foundation repair to solar panel installation. She brings more than 15 years of writing and editing experience to bear in her meticulous approach to ensuring accurate, up-to-date, and engaging content. She’s previously edited for outlets including MSN, Architectural Digest, and Better Homes & Gardens. An alumna of the University of Pennsylvania, Roxanne is now an Oklahoma homeowner, DIY enthusiast, and the proud parent of a playful pug.

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