What is the purpose of a liquid-line filter-drier and where should it be installed?

• A. To filter oil in the compressor crankcase.
• B. To trap moisture and particulates in the liquid line; installed between condenser and metering device.
• C. To regulate pressure in the liquid line.
• D. To cool refrigerant in the liquid line after the metering device.

Answer: (B)

The liquid-line filter-drier’s job is to remove moisture and particulates from the refrigerant as it flows in the liquid line, protecting the metering device and the rest of the system. Moisture in the liquid can flash into vapor at the expansion device, causing ice blockages, corrosion, and potential acid formation that can degrade oil and components. Particulates can clog the small passages in the metering device. The drier absorbs moisture with desiccant and filters out debris, keeping the liquid entering the expansion device clean and dry.

It should be installed in the liquid line after the condenser and before the metering device, so the high-pressure liquid refrigerant reaching the expansion device is protected. This isn’t about filtering compressor oil, regulating pressure, or cooling the refrigerant—those are separate functions handled by other components.