How are refrigerant fluids classified?

Regarding the identification of halogenated hydrocarbons, they are univocally designed with initials based on ASHRAE nomenclature (American Society of Heating, Refrigerating and Air Conditioning Engineers). Like the AHRI (Air Conditioning and Refrigeration Institute) and its definition of marketing specifications for refrigerant fluids, said organisation is not a regulatory institution. However, its identification of refrigerant fluids is a landmark that is universally acknowledged and accepted by companies. As a rule of thumb, a refrigerant fluid is designated by the letter R followed by three digits: e.g. R 134, R 404

The first digit indicates the number of carbon atoms contained in the molecule minus one unit; the second digit is the number of hydrogen atoms of the molecule plus one unit; the third is the number of fluorine atoms, while any chlorine atoms are calculated based on the difference, knowing the total number of bonds of the molecule (which are double the number of carbon atoms increased by two units). Moreover, if the first digit is 4 or 5, the code refers to a blend of refrigerant fluids that is respectively geotropic (not azeotropic) or azeotropic. If there are double carbon bonds, a fourth digit indicating the number of said bonds will precede the others. Lastly, a lower case letter (a, b, …) on the right of the digits for ethane derivatives (first digit equal to 1) indicates the molecule's growing asymmetry