RS-52 (R428A)

RS-52 is a non flammable blend of HFC 125, HFC 143a, isobutane and propane which has a zero ODP and is also compatible with both traditional and synthetic lubricants so that a retrofit is not required.

RS-52 is a “Drop-in” replacement for R502 providing an easy and at the same time a long term solution. 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-52 has significantly lower discharge temperatures and pressures than R502 which removes the problem of oil decomposition and also widens the applications for RS-52


RS-52 is suitable for use as a replacement for R502 in existing commercial and industrial air conditioning and refrigeration systems, and appliances.

Service Work

Because it is a blend, it is a recommended that RS-52 be charged into systems as a liquid as opposed to the gaseous phase. Since there is no need to change the existing lubricant, RS-52 is straightforward to use, as the following procedure outlines.

Conversion procedure for replacing R-502 with RS-52

  • 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-502 charge and weigh recovered amount of R502 to determine amount of RS-52 to be charged.
  • RS-52 is compatible with MO/AB and POE oils. If however the oil in the system is being changed to a different type it is not necessary to remove all the existing oil in the system.
  • Replace the filter/drier
  • Evacuate the system and liquid charge with RS-52, am amount approx. 10% less than the original charge of R-502.
  • 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-52 may be added. Avoid overcharging the system.
  • Check system thoroughly for leaks.
  • Clearly label sytem as charged with RS-52 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-52 oil return capabilities with alklybenzene or polyolester oils.


RS-52 is compatible with both mineral and alkylbenzene oils found in R502 systems, and also with the polyoester lubricants. Therefore, there is no need to change the lubricant although compressor manufacturers’ recommendations regarding lubricity should be followed.

Materials Compatibility

RS-52 is compatible with all materials commonly used in refrigeration systems previously charged with R502. In general, materials which are compatible with R502 can be used with RS-52. It is recommended to check equipment manufacturer’s retrofit literature and obtain recommendations from equipment manufacturers with regard to materials’ compatibility.

Environmental Data

None of the components of RS-52 contains chlorine so that it has no ability to deplete the ozone layer.
As with all the hydrofluorocarbons (HFCs), RS-52 does have a direct global warming potential (GWP), but this is counterbalanced by its lower Total Equivalent Warming Impact (TEWI).


HFC 125
HFC 143a
Chemical name Pentafluoroethane/1,1,1,-Trifluoroethane/Isobutane/Propane
Type HFC blend
CFC Replacement R502
HCFC Replacement R-22 (low temp), R-408A (FX10), R-401A (HP80)
Temperature glide Approximately 0.9°C
Drop-in or long term Both
Lubricant MO/AB/POE
ODP Zero
Atmospheric lifetime 37 years
GWP 100 year ITH
500 year ITH

RS-52 Physical Properties

RS-52 R502
Molecular weight 101.3 111.6
Boiling point (1 atm) °C -46.7(1) -45.4
°F -52.1(1) -49.7
Temperature glide °C 0.8 0.2
Critical temperature °C 73.0 82.2
°F 163.4 180.0
Critical pressure bara 38.1 40.7
psia 552 59.1
Liquid density at 25°C Kg/m3 1053 1217
Density of saturated vapour at 25°C kg/m3 70.2 62.2
Specific heat of liquid at 25°C kj/kg°C 1.52 1.25
Specific heat of vapour at 1 atm & 25°C kj/kg°C 0.706
Vapour pressure at 25°C bara 12.68(1) 11.5
psia 183.9(1) 167
Latent heat of vaporisation at boiling point kj/kg 189.2(1) 173
Ozone Depletion Potential ODP 0 0.33
Flammability limit in air (1 atm) vol% None None
Inhalation exposure (8 hr day & 40 hr week) ppm 1000 1000