I was studying the designation of names to refrigerants.

The following is the basic formula:

R - (m - 1) ( n + 1) ( o )

m = number of carbon atoms in the refrigerant
n = number of hydrogen atoms in the refrigerant
o = number of fluorine atoms in the refrigerant

So R-134a has:

1 + 1 = 2 carbon atoms
3 - 1 = 2 hydrogen atoms
4 fluorine atoms

What does the 'a' at the end mean?


2 Answers 2


R134a..Here "a" is used to denote that it is an isomer. R134 and R134a have same chemical formula and atomic weight but different chemical structures.

R134 has NBP of about -19 C whereas R134a has a NBP of about -26C.

And dont use capital 'A' in R134a …. "A" denotes that the refrigerant is non -azeotropic.


  • $\begingroup$ same chemical formula and atomic weight but different chemical structures so does this affect the properties of the refrigerant ? I mean are thermal properties of R134 and R134a different? $\endgroup$
    – Fennekin
    Commented Feb 8, 2016 at 18:16
  • $\begingroup$ @Fennekin Correct. "R134" is not useful as a refrigerant due to its molecular properties. A similar trend appears in pharmaceuticals with different isomers of a drug. $\endgroup$
    – morristtu
    Commented Feb 8, 2016 at 18:21

If a refrigerant contains 'a' at its end it is the isomer of that refrigerant. Example 'R123' is 'C2H2F3Cl2' and 'R123a' is the isomer of the same molecule.


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