A refrigerant is most often a fluid that is a mixture used in the HVAC cycle. It undergoes transitions from a liquid to a gas and back to a liquid. Refrigerants can be propane, hydrocarbons, ammonia, fluorocarbons, hydrofluorocarbons, and hydrochlorofluorocarbons. They may be further defined as being azeotropic and zeotropic.

In the early days of HVAC, refrigeration systems used sulfur dioxide, ammonia, and methyl chloride. Sulfur dioxide and methyl chloride are toxic and soon fell into disuse being replaced by chlorofluorocarbons. At times, methyl formate, chloromethane, and dichloromethane may be found in very old units.

Legislation has changed which compound may be used as regulations have been created for chlorofluorocarbons and hydrochlorofluorocarbons. Across the board, legislation has become more demanding as an attempt to control depletion of the ozone layer of the atmosphere.

To be an acceptable refrigerant, it must be certain prerequisites and compound behavior expectations.

  • It must meet standards as set forth by the Environmental Protection Agency.

  • It should not be toxic.

  • It should not explode.

  • It should not corrode.

  • It must not be flammable.

  • It must make leak detection easy.

  • It should have a low boiling point.

  • It should be a stable gas.

  • It should lubricate all internal parts of the compressor.

  • It should have a high liquid volume per pound.

  • It should have a high latent heat per pound.

  • It shoud have a low vapor volume per pound.

  • Pressure differences between evaporating pressure and condensing pressure should be low.

Colors and Coding

Because refrigerants possess varying levels of toxicity and flammability, it is necessary to code them for safety. It is also handy to know colors and coding in order to select the correct refrigerant when charging a system. Cross charging of refrigerants is not only harmful to an HVAC system, but is actually illegal.

There are twenty-nine different colors used in the color coding scheme devised by the American Society of Heating, Refrigerating and Air-Conditioning Engineers(ASHRAE). This organization oversees policy and regulations for the HVAC industry and is influential in legislation governing the installation and maintenance of HVAC systems in the United States.

Recovered refrigerants are most often placed in gray cylinders with yellow ends.

Numbers and Coding

Refrigerants are defined as having certain properties and compositions that determine their usage. A numbering system has been created by ASRAE to make decisions regarding usage easier. The numbering system is based on the refrigerants chemical makeup and unique properties.

The following is a breakdown of the basic numbering system.

  • 000-Methane-based compounds

  • 100-Ethane-based compounds

  • 200-Propane-based compounds

  • 300-Cyclic organic compounds

  • 400-Zeotropes

  • 500-Azeotropes

  • 600-Organic compounds

  • 700-Inorganic compounds

  • 1000-Unsaturated organic compounds

Classes and Coding

Further, refrigerants are divided into classifications numbering one through three. The classification system is based on the compounds manner of absorption and the method of heat extraction.

  1. Class 1: These are refrigerants that cool by phase change or boiling and uses the refrigerant’s latent heat.

  2. Class 2: These cool by a temperature change. They are calcium chloride brine, air, sodium chloride brine, alcohol, and other nonfreezing solutions. They are designed to reduce temperature and convey the lower temperature to the environment being conditioned.

  3. Class 3: These are solutions and compounds that contain absorbed vapors or liquefiable agents. They are able to carry vapors that may be liquified.

The correct identification and classification of all refrigerants is highly regulated and protected by law.