A liquid line drier is key to battling a formidable opponent: moisture. That makes it one of the most important — yet least expensive — parts of a refrigeration system.

Moisture is a major cause of compressor failure. It can interact with halocarbon refrigerants and turn into hydrochloric and hydrofluoric acid, which, over time, will destroy components, as well as soften and eat away the insulation from the compressor motor windings.

The liquid line drier’s main function is removing moisture. It can also catch particulates such as copper chips or small pieces of debris, preventing them from ending up where they can cause damage. Whenever a system is opened for service, it is always a good idea to replace the liquid line drier.

In an operating system, if there is a moisture indicator and it shows caution or moisture, the drier needs to be replaced. Also, a pressure or temperature drop across the drier indicates it is becoming clogged. Check the temperature of the line entering and leaving the drier. If there is more than 1°F difference or more than a 2 psig drop, replace the drier.

In a new installation, the drier will normally be in the liquid line, just outside of the receiver. Install a sight glass/moisture indicator immediately after the drier to give the vacuum pump ample time to remove air and moisture.

When replacing a failed compressor, locate the drier as close to the expansion valve as possible to ensure any contaminants or particulates in the liquid line are trapped in the drier. Adding a suction filter as close to the compressor as possible will help catch debris and protect the new compressor.

Using a larger drier with more desiccant, like a 303S instead of a 163S, or a replaceable core drier that is replaced after a certain amount of run time, can help clean up the system and extend the life of the replacement compressor. Vacuuming properly during install and service is also important to moisture removal.

Choosing the Correct Drier

Understanding the different properties of drier media will help you choose the correct drier for the system. The two main types of desiccants used in driers are:

1. Activated alumina, which can capture larger amounts of moisture to help lengthen the drier’s life; and
2. Molecular sieve-type driers, which not only capture moisture, but also help with acid in a contaminated system.

Liquid line driers come in different sizes for both the line size and amount of desiccant in the drier. A 163S drier, for example, contains 16 cubic inches of desiccant and fits a 3/8-inch line. A 083S drier fits the same size line but only has half as much desiccant, while a 164 SAE drier is a flare style for a half-inch line. The first numbers are desiccant volume, and the last digit is line size in 1/8-inch increments. The letter S denotes sweat or braze, and SAE is the flare type.

Standard driers are directional and have a flow arrow stamped on them. Heat pump systems require a bi-flow drier. A chart on the drier box lists the refrigerants it works with and the tonnage of the system it can handle. This typically applies to a system that is in good working order. A system contaminated by a burned out compressor — or one with moisture — may need a much larger drier. A drier may have gauge ports on one or both sides to read pressure drop.

Suction filters can be used on the suction line, and using a suction filter in conjunction with a liquid line drier can offer maximum cleanup of a contaminated system. Suction filters can be a desiccant type or made with just a filtration media. Which type you select is determined by system contamination. Replaceable core styles are available for both liquid driers and suction filters and are a good option for contaminated and larger systems that will require multiple drier changes.

Installing the Drier

After system repair or compressor replacement, the drier should be the last thing installed. Uncap it as briefly as possible before installation.

Once the system has been put back into service — and after several days or weeks of normal operation – you should replace the liquid line drier and remove the suction filter. Testing the refrigerant and oil for acid after replacing a failed compressor will help determine if additional drier changes are warranted.

Replacing driers is far cheaper than having additional failures and lost product. Keeping a refrigeration system clean and dry by changing the liquid line drier — together with routine maintenance — can be the least expensive insurance against failure.