Everyone who works with refrigeration systems knows that the quality of the refrigerants is important. Suppliers ensure that new refrigerants are free of contaminants before they ship them, and they carefully clean and check any recovered refrigerants before certifying them for reuse. The oils that are used in a refrigeration system also must be clean and contaminant-free to ensure that the equipment will operate properly. Using clean refrigerants and oils certainly is one requirement for having a clean refrigeration system.
Sometimes, however, the problem is not the quality of what is put into the system, but contaminants that have entered the system through other means. Refrigerants are good cleaners and tend to do a decent job of picking up loose particulate matter (rust, metal filings, dirt, welding smoke and slag, for example) and keeping it in suspension. Because refrigeration systems are closed systems, though, any “dirt” in the system will stay in the system, in constant motion with the refrigerant, unless it is removed.