What is the purpose of a filter-dryer in an ammonia refrigeration system?

• A. It absorbs moisture from the oil.
• B. It filters contaminants from the circulating refrigerant only.
• C. It removes moisture and contaminants from circulating refrigerant.
• D. It helps balance refrigerant charge.

Answer: (C)

The main idea is that the filter-dryer cleans the circulating refrigerant by removing both moisture and contaminants. In ammonia systems, moisture is a major troublemaker: it can react with ammonia and oil to form corrosive substances, promote rust, and even freeze in expansion devices, causing blockages. Contaminants and degraded oil particles can wear or clog valves, metering devices, and compressors. The filter-dryer uses desiccant to adsorb water and a filtering element to trap solids, giving dry, clean refrigerant that protects critical components and the oil circuit. It’s typically placed in the liquid line before the metering device so moisture and debris don’t reach the expansion device or compressor. While it also helps keep the oil cleaner by reducing carried-in moisture, its primary purpose is removing moisture and contaminants from circulating refrigerant. It does not serve to balance the refrigerant charge.