Refrigerant blend compositions
The table
| Blend | Composition | Behaviour | GWP (AR4) | We stock |
|---|---|---|---|---|
| R-410A | R-32/R-125 (50/50) | Near-azeotropic | 2,088 | Stocked |
| R-404A | R-125/R-143a/R-134a | Near-azeotropic | 3,922 | Stocked |
| R-407C | R-32/R-125/R-134a | Zeotropic | 1,774 | Stocked |
| R-448A | R-32/R-125/R-1234yf/R-134a/R-1234ze (26/26/20/21/7) | Zeotropic | 1,387 | Stocked |
| R-508B | R-23/R-116 (46/54) | Zeotropic | 13,396 | Stocked |
| R-407A | R-32/R-125/R-134a | Zeotropic | 2,107 | — |
| R-407F | R-32/R-125/R-134a | Zeotropic | 1,825 | — |
| R-427A | R-32/R-125/R-143a/R-134a | Near-azeotropic | 2,024 | — |
| R-438A | R-32/R-125/R-134a/R-600/R-601a | Near-azeotropic | 2,265 | — |
| R-454B | R-32/R-1234yf | Near-azeotropic | 466 | — |
Compositions are nominal mass fractions as designated under ASHRAE Standard 34. GWP figures are mass-weighted IPCC AR4 values.
Why composition decides the handling
A zeotropic blend's components have different boiling points. Draw vapour from the cylinder and the more volatile component leaves first, so the vapour entering the system is richer in it and the liquid left behind is poorer. Do that repeatedly and neither the cylinder nor the system contains the designated product any more.
That is the entire reason for the liquid-charging rule. Invert the cylinder or use the liquid valve, and meter into the low side so the compressor is not slugged.
The same physics produces temperature glide: the blend evaporates across a range of temperatures rather than at one, which changes how superheat and subcooling are measured. Use dew point for superheat and bubble point for subcooling. See glide explained.
The R-125 problem
Reading down the composition column, one component keeps appearing: R-125, with a GWP of 3,500. It is in R-410A, R-404A, R-407C, R-427A, R-438A and R-448A.
R-125 is there because it suppresses flammability. R-32 on its own is A2L; blended with enough R-125 the mixture becomes A1. The industry bought non-flammability with climate impact, and that trade is what the Kigali phase-down is now unwinding, which is why the newer blends such as R-448A and R-454B cut the R-125 fraction and accept A1 or A2L classification accordingly.
What the number tells you
The 400 series is zeotropic, the 500 series is azeotropic. The letter suffix distinguishes blends with the same components in different proportions: R-407A, R-407C and R-407F are all R-32, R-125 and R-134a, mixed differently for different duty.
That is why the letter is not optional. R-407A and R-407C are not the same product and do not go into the same machine. See the numbering guide.
Quick answers
What is R-410A made of?
Equal parts R-32 and R-125 by weight. It is near-azeotropic, so it behaves almost like a single fluid but should still be charged as a liquid.
What is the difference between R-407A, R-407C and R-407F?
All three contain R-32, R-125 and R-134a in different proportions, for different duty. They are not interchangeable.
Why must zeotropic blends be charged as liquid?
Their components boil at different temperatures. Vapour charging removes the more volatile component first, changing the composition of both the cylinder and the system.
What is R-508B made of?
R-23 and R-116, roughly 46 to 54 by weight. It is azeotropic, so it behaves as a single fluid with no glide.
- ASHRAE Standard 34 · refrigerant designation, blend numbering and composition · ashrae.org.
- IPCC Fourth Assessment Report · component GWP values · ipcc.ch.
- AHRI Standard 700 · composition tolerances for blended refrigerants · ahrinet.org.
This guide is general information compiled from the cited sources — not legal, safety or engineering advice. Read our full disclaimer.
Related: Zeotropic vs azeotropic · What the R-numbers mean · GWP table · Can you mix refrigerants?