commonly subjected in service. The cylinder code color for R-12 is white.

R-22 MONOCHLORODIFLUOROMETHANE (CHCIF₂ )

Monochlorodifluoromethane, normally called R-22, is a synthetic refrigerant developed for refrigeration systems that need a low-evaporating temperature, which explains its extensive use in household refrigerators and window air conditioners. R-22 is nontoxic, noncorrosive, nonflammable, and has a boiling point of -41F at atmospheric pressure. R-22 can be used with reciprocating or centrifugal compressors. Water mixes readily with R-22, so larger amounts of desiccant are needed in the filter-driers to dry the refrigerant. The cylinder code color for R-22 is green.

R-502 REFRIGERANT (CHCIF₂ /CCIF₂ CF₃ )

R-502 is an azeotropic mixture of 48.8 percent R-22 and 51.2 percent R-115. Azeotropic refrigerants are liquid mixtures of refrigerants that exhibit a constant maximum and minimum boiling point. These mixtures act as a single refrigerant. R-502 is noncorrosive, nonflammable, practically nontoxic, and has a boiling point of -50F at atmospheric pressure. This refrigerant can only be used with reciprocating compressors. It is most often used in refrigeration applications for commercial frozen food equipment, such as frozen food walk-in refrigerators, frozen food display cases, and frozen food processing plants. The cylinder color code for R-502 is orchid.

R-134a TETRAFLUOROETHANE (CH₂ FCF₃ )

R-134a, tetrafluoroethane, is very similar to R-12, the major difference is that R-134a has no harmful influence on the ozone layer of the earth's atmosphere and is a replacement for R-12 applications. Noncorrosive, nonflammable, and nontoxic, it has a boiling point of -15F at atmospheric pressure. Used for medium-temperature applications, such as air conditioning and commercial refrigeration, this refrigerant is now used in automobile air-conditioners. The cylinder color code for R-134a is light (sky) blue.

ADDITIONAL REFRIGERANTS

In addition to the previously mentioned refrigerants, other less common refrigerants are used in a variety of applications.

R-717 Ammonia (NH₃ )

Ammonia, R-717, is commonly used in industrial systems. It has a boiling point of -28F at atmospheric pressure. This property makes it possible to have refrigeration at temperatures considerably below zero without using pressure below atmospheric in the evaporator. Normally it is a colorless gas, is slightly flammable, and, with proper portions of air, it can form an explosive mixture, but accidents are rare. The cylinder color code for R-717 is silver.

R-125 Pentafluoroethane (CHCF₅ )

Pentafluoroethane, R-125, is a blend component used in low- and medium-temperature applications. With a boiling point of -55.3F at atmospheric pressure, R-125 is nontoxic, nonflammable, and noncorrosive. R-125 is one replacement refrigerant for R-502.

All refrigerants have their own characteristics. It is extremely important to charge a system with the refrigerant specified. Use of an incorrect refrigerant can lead to reduced efficiency, mechanical problems, and dangerous conditions.

OZONE PROTECTION AND THE CLEAN AIR ACT

Several scientific studies conducted in the 1970s showed that chlorine was a leading cause of holes in the ozone. In 1987, 30 countries signed the Montreal Protocol, which mandated the phase out of the production, and eventual use, of all harmful CFCs. In 1990, the most significant piece of legislation affecting the air conditioning and refrigeration industry, the Clean Air Act, was passed. Regulated by the Environmental Protection Agency (EPA), Title VI of the Clean Air Act states fully halogenated refrigerants (CFCs) will be phased out. It also calls for the phase out of HCFCs by the year 2030. Both of these types of refrigerants adversely affect the atmosphere, and as of July 1992, it is illegal to discharge refrigerant to the atmosphere. The production of R-12 was discontinued in December 1995, and the production of R-11, R-113, R-114, and R-115 is scheduled to be discontinued by