Which refrigerant is specifically mentioned for use in medium-pressure appliances?

R-12 is specified for use in medium-pressure appliances because it operates at a pressure range that allows it to effectively function in that capacity. Medium-pressure refrigerants are designed to provide cooling and heating in systems that require certain temperature and pressure characteristics. R-12, a chlorofluorocarbon (CFC), has been widely used in refrigeration and air conditioning systems.

In contrast, the other refrigerants listed have different applications or pressure classifications. R-22 is categorized as a low-pressure refrigerant, while R-123 and R-11 are considered high-pressure refrigerants. Each refrigerant is designed for specific systems depending on the intended use and operational pressures, which highlights the importance of selecting the correct refrigerant for efficiency and compliance with regulations. R-12's designation makes it a viable choice for medium-pressure systems compared to the others, which do not fit that classification as accurately.