How to Size Up Liquid Line Driers

Determine what type of refrigerant your air conditioner or refrigeration system uses. You'll need a drier for the type you use. For instance, if you use R-22, you'll require a drier that has a higher capacity rating and a larger physical size, while R-12 driers will be smaller in rating and size.

Examine the drier's model number. The first two numbers will denote the cubic inch capacity of the drier, while the last number indicates the diameter of the fitting (size) measured in eights of an inch. For instance, 032 indicates a drier of 3 cubic inches, with a 2/8-inch (1/4) line fitting size. You can also determine its flare and nut fittings, e.g., a 163S drier rating indicates a 16-cubic-inch capacity, with a 3/8-diameter line fitting. The "S" stands for sweat, or brazened construction, meaning a permanent attachment.

Use an outside micrometer to measure the size of your line fitting by placing the micrometer probes over the outside of the line. This will give you the fitting size you need for your drier. Use a tape measure to gauge the distance between any wall, component or other obstruction to the location of the liquid line that might inhibit the location of the drier, if you're installing one for the first time on your system. Measure the liquid line to the obstruction, allowing half the diameter of the drier canister to fit within that location.

Look at the specifications on your drier to determine the amount of "water drops removed." Check your unit specification manual to see what your unit requires. Match the drier and water drops removed with your manufacturer's recommendation. Also record the "tons" on the drier and on your unit, making sure the ton capacity requirements are met or exceeded by the drier's capability.

Determine what chemical refrigerant you have, whether it's CFC, HCFC or HFC. All these must use a drier that can eliminate a maximum allowable moisture content of 15 parts per million (PPM). Any drier with a rating below 15 PPM will be adequate for your use, unless your unit service manual specifies otherwise.

Decide what kind of fitting you'll need to connect the drier to the liquid line, if this is a first-time installation, or you intend to change the fitting configuration. Sweated or brazened lines work well on larger AC and refrigeration systems due to their permanent attachment. Sweated fittings also negate the possibility of leaks at extra joints in the lines. Flare nut fittings make the drier more accessible for changing and replacement, and can be used on smaller units successfully. However, flare nut fittings can be prone to leaking, due to corrosion and stripped threads.