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RS-24 (R426A)

Type and Description

RS-24 is a non flammable blend of HFC 134a, HFC 125, butane and isopentane which has a zero ODP and is also compatible with both traditional and synthetic lubricants so that a retrofit is not required. RS-24 is a “Drop-in” alternative for R12 which also provides a long term solution at the same time. It provides, therefore, a one change solution to the replacement of R12 at minimal expense. Because there is no need to use expensive and hygroscopic synthetic lubricants, the risk of moisture ingress into a refrigeration system is completely avoided. RS-24 has lower discharge temperatures than R12 thereby reducing degradability of the lubricant in the system.


RS-24 can be used in all the main applications used where R12 is present including mobile air conditioning, hermetic and semi-hermetic compressor systems, cold stores, refrigerated transport, dairy chillers, vending machines, cellar cooling etc…

RS-24 is an excellent performance match for R12 providing a similar performance in almost every respect.

Service Work

Because it is a blend, it is recommended that RS-24 be charged into systems in the liquid as opposed to the gaseous phase.

Since there is no need to change the existing lubricant, RS-24 is straightforward to use as, the following procedure outlines.

Conversion Procedure for replacing R-12 with RS-24


  • Ensure the right equipment is available, e.g. Recovery unit and cylinders, container for recovered lubricant, vacuum pump, weighing scales, replacement drier etc…
  • Record baseline data to establish the normal operating conditions for the equipment.
  • Recover the R-12 charge and weigh recovered amount of R12 to determine amount of RS-24 to be charged.

    IMPORTANT: Never top up a R-12 system with RS-24. When RS-24 and R-12 are mixed Azeotropic mixtures can be formed which will affect performance and may harm the system.
  • RS-24 is compatible with MO/AB and PAG oils. If however the oil in the system is being changed, it is not necessary to remove all of the existing oil in the system.
  • Replace the filter/drier
  • Exacuate the system and liquid charge with RS-24. 10% less RS-24 will be required than the R12 being replaced. Avoid overcharging the system.
  • Start the system and check baseline data, adjust the expansion device if required. If a low pressure control functions as a temperature control, check the space temperature and adjust if necessary.
  • If the system is fitted with a refrigerant sight-glass and the sight-glass is not indicating a full charge additional RS-24 may be added. Avoid overcharging the system.
  • Check system thoroughly for leaks.
  • Clearly label system as charged with RS-24 and type of oil used.
  • On larger systems fitted with an oil sight-glass. Check oil level after several hours of operation and add oil if necessary.

NOTE: Systems with inherent poor oil return, such as systems with unusually long suction lines and/or low temperature systems, may have improved RS-24 oil return capabilities with alkylbenzene or polyolester oils.


RS-24 is compatible with both mineral and alkylbenzene oils found in R12 systems, and also with the synthetic oils POE and PAG. Therefore, there is no need to change the lubricant although compressor manufacturers’ recommendations regarding lubricity should be followed.

Materials Compatibility

RS-24 is compatible with all materials commonly used in refrigeration systems previously charged with R12. In general, materials which are compatible with R12 can be used with RS-24. It is recommended to check equipment manufacturer’s retrofit literature and obtain recommendations from equipment manufacturers with regard to material’s compatibility.

Environmental Data

None of the components of RS-24 contains chlorine so that it has no ability to deplete the ozone layer.

As with all hydrofluorocarbons (HFCs), RS-24 does have a direct global warming potential (GWP), but this is counterbalanced by its lower Total Equivalent Warming Impact (TEWI) than R12. RS-24 has a relatively short atmospheric lifetime of approximately 15 years which is at the lower end of the main HFCs available today and compares to over 100 years in the case of R12.


HFC 134a

HFC 125


Chemical name 1,1,1,2-tetrafluoroethane / Pentafluoroethane / butane / isopentane
Type HFC blend
CFC replacement R12
Temperature glide Approximately 0.5°C
Drop-in or long term Both
Lubricant MO/AB/POE
ODP Zero
Atmospheric lifetime 15 years
GWP 100 year ITH

500 year ITH

RS-24 Physical Properties

    RS-24 R12
Molecular weight   102.6 120.9
Boiling point (1 atm) °C -28.6 -29.8
°F -19.5 -21.6
Temperature glide °C 0.5 0
Critical temperature °C 101.0 112.0
°F 213.8 233.6
Critical pressure bara 4097 4116
psia 594 597
Liquid density at 25°C Kg/m3 1184 1311
Density of saturated vapour at 25°C kg/m3 30.9 37.3
Specific heat of liquid at 25°C kj/kg°C 1.45 1.00
Specific heat of vapour at 1 atm & 25°C kj/kg°C 0.863 0.606
Vapour pressure at 25°C kpa 707 643
psia 102.6 93.3
Latent heat of vaporisation at boiling point kj/kg 218 165
Ozone Depletion Potential ODP 0 1
Flammability in air (1 atm) vol% None None
Inhalation exposure (8 hr day & 40 hr week) ppm 1000 1000