R-424A (RS-44) PT Chart and Refrigerant Profile

Where you will find R-424A

R-424A is RS-44, a no-oil-change R-22 retrofit blend made by Refrigerant Solutions Ltd in the UK. ACHR News reported its US launch in 2007 through ComStar International, which imported it from RSL. A-Gas now markets RS-44 in the UK and Canada, and lists it for medium- and high-temperature AC and refrigeration: commercial AC, commercial refrigeration and transport units (A-Gas UK).

You will find it in R-22 split systems, rooftops and condensing units converted since its 2006 SNAP listing. The nameplate still says R-22, so read the retrofit label. Guideline N-2017 Table 1 assigns R-424A black, with no PMS number; on cylinders made since 2020 that color appears only on the label.

It is one of several five-component R-22 drop-ins with small hydrocarbon additions. R-438A (MO99) and R-453A (RS-70) are relatives with different mixes, so never read one chart for another.

Charging R-424A

Charge from the liquid phase. A-Gas UK says it must be charged as liquid. The Gasco FAQ adds that vapor charging is acceptable only if the whole cylinder goes into the system, because the cylinder’s vapor and liquid differ in composition.

This blend has real glide: 7.8°F at a 40°F dew point and 5.7°F at a 100°F bubble point. Use the columns correctly:

• Superheat: suction pressure against the dew column. At 40°F this chart gives 55.1 psig dew and 65.5 psig bubble; reading the bubble column would make the superheat look several degrees higher than it is. Fixed orifices go by target superheat.
• Subcooling: liquid-line pressure against the bubble column. TXV and EEV systems go by the manufacturer’s subcooling target.

Compared with R-22 (68.6 psig at 40°F), suction pressure at the same evaporator dew point is lower. Head pressure is close: 189.2 psig bubble at 100°F against 195.9 psig for R-22.

For a conversion, A-Gas’s general retrofit guide puts the initial charge at 90–95% by weight of the original R-22 charge. Add from there to the equipment’s targets. The temperature glide calculator shows the gap at any pressure.

Oil and compatibility

Sources agree it runs with the existing oil in most systems, but not all:

• A-Gas Canada: compatible with existing oils, no hardware changes.
• A-Gas UK: generally compatible with mineral oil, but conversion to POE may be needed in some cases; check with the compressor maker.
• Gasco: mineral oil, AB or POE; a partial POE addition, about 25%, may be needed with long or complex piping, large receivers or very low evaporating temperatures.

Replace the filter-drier and evacuate to the OEM target before charging (evacuation guide). See the refrigerant oil guide.

Safety, handling and recovery

R-424A is A1 (lower toxicity, no flame propagation) per A-Gas, Gasco and EPA. The hydrocarbon content totals 2.5%.

It is a Section 608 high-pressure refrigerant: its computed liquid saturation pressure at 104°F is 215.5 psia (200.8 psig, bubble). Type II or Universal certification covers it, and sales have been limited to certified technicians since Jan 1 2018. Recover appliances made after Nov 15 1993 to 0 in Hg under 200 lb of charge and 10 in Hg at 200 lb or more (refrigerant recovery). Keep it in its own recovery cylinder, labeled R-424A.

Status and replacements

EPA SNAP lists R-424A as acceptable, retrofit and new, since Sept 28 2006 in residential and light commercial AC, industrial process AC and refrigeration, remote condensing units, supermarket systems, refrigerated transport, ice machines, ice rinks and dehumidifiers. In new centrifugal and positive-displacement chillers it has been unacceptable since Jan 1 2024, except under a narrowed use limit.

Its AR4 GWP of about 2,440 is above every Technology Transitions limit for new equipment, and 40 CFR 84.54 names it, and separately “RS-44 (2003 formulation)”, for new refrigerated transport from Jan 1 2025. Servicing and retrofitting existing equipment remain legal. HFC supply falls to 30% of baseline in 2029–2033 under the AIM Act.

Availability is the practical problem. A-Gas Canada calls RS-44 a legacy product being replaced by RS-70. A 2026 ChemPoint page for ComStar lists RS-44b (R-453A) rather than RS-44. We could not confirm a current US distributor. For other routes off R-22, see R-22 replacement options and R-22 vs MO99.

Common questions

Is R-424A a drop-in for R-22?

It is sold as a no-oil-change R-22 retrofit, and EPA accepts it for retrofitting R-22 AC. A-Gas UK still says some systems may need POE, and the charge is weighed in fresh after recovering the R-22.

What replaced RS-44?

A-Gas Canada says RS-44 is being replaced by RS-70. In the US, the RS-44b name belongs to R-453A.