R-502 Replacement Refrigerants

What changes in the field

The HFC replacements run higher than R-502. From the PT data, at 40°F evaporating (dew) R-502 reads 77.5 psig, R-404A 85.4 and R-507A 89.2. At 100°F condensing (bubble) R-502 is 211.8 psig, R-404A 236.8 and R-507A 242.3. Arkema’s retrofit guide puts R-404A at 0-5 psi higher suction and 15-25 psi higher discharge than R-502, and R-507A at 0-5 psi higher suction and 20-35 psi higher discharge.

The R-502 values on this site read low. The R-502 chart is computed as an R-22/R-115 mixture, and that model sits about 2% below the National Refrigerants reference table, about 1 psi at low temperature and up to about 5 psi at condensing temperatures. Our R-502 numbers above are therefore a few psi low, and the real gap to R-404A and R-507A is a little smaller. Use the NRI R-502 table where a few psi matter.

The service blends stay closer. Arkema gives R-408A 1-3 psi lower suction and 0-5 psi higher discharge than R-502, and NRI describes it as having similar PT properties across the operating range. NRI lists R-402A for low-temperature work with a higher discharge pressure and lower discharge temperature than R-502. Use the blend’s own PT chart: R-408A. This site does not publish an R-402A chart, because the open equation-of-state model reads about 4% low against Arkema’s and NRI’s published values; use the manufacturer’s chart for R-402A.

Glide is small for R-502, R-404A and R-507A (computed 0.3°F, 0.9°F and under 0.1°F at 40°F evaporating). The service blends are zeotropes; read dew for superheat and bubble for subcooling. All five are A1 and use a standard AHRI 740 recovery machine. Keep each in its own recovery cylinder.

Retrofit or replacement

Never top off R-502 with any of these. Recover the full R-502 charge, weigh it, and then follow the refrigerant maker’s procedure. Arkema’s quick reference, which it calls general guidelines that vary by system:

1. Follow the OEM’s retrofit recommendations and change to a filter-drier suited to the new refrigerant.
2. For R-404A or R-507A, change the oil to POE. BITZER says polyol esters are the suitable lubricants for these HFCs and that elastomers must be adapted. Arkema’s technical digest calls for reducing residual mineral oil to 5% or less when moving from R-502 to R-507A.
3. For R-408A, no oil change is required. NRI lists mineral oil, alkylbenzene and POE as compatible with both R-408A and R-402A; BITZER says the R-22 and propane content of these blends lets them run on conventional oils.
4. Charge as liquid. Arkema’s starting charge is 85-90% of the R-502 weight for R-404A, R-507A and R-408A. Arkema says R-507A should be charged in liquid phase even though it is an azeotrope.
5. Adjust to the equipment’s superheat or subcooling target and label the system with refrigerant and oil.

Discharge temperature decides some jobs. Arkema puts R-408A 10-35°F hotter than R-502, while R-404A and R-507A run 0-10°F cooler. BITZER notes that service blends tuned to match R-502 capacity run higher discharge temperatures, which limits them in high-superheat work such as supermarkets.

When the equipment is being replaced rather than converted, new low- and medium-temperature systems no longer use R-404A or R-507A; see R-404A replacement and R-404A vs R-507A.

Capacity, efficiency and cost

BITZER says the performance of R-404A and R-507A “is very similar to R502”, with a similar or lower discharge temperature. None of the sources used here gives a capacity or efficiency percentage for R-402A or R-408A against R-502, so none is quoted.

Supply drives the choice. R-502 contains CFC-115, banned from US production and import since Jan 1 1996, so service relies on recovered, reclaimed or stockpiled refrigerant. R-402A and R-408A contain HCFC-22, whose US production and import ended Jan 1 2020, and BITZER says production of most R-502 service blends has been discontinued. Check availability before planning around one.

R-404A (AR4 GWP 3,922) and R-507A (3,985) are in production, but under 40 CFR 84.54 they are not allowed in most new commercial refrigeration systems. Servicing existing systems with them is allowed. From Jan 1 2029, servicing supermarket systems, refrigerated transport and automatic commercial ice makers must use reclaimed refrigerant (40 CFR 84.112(e)).

Common questions

Is there a drop-in replacement for R-502?

No true drop-in. R-408A and R-402A come closest by keeping the existing oil, but they are R-22-based and mostly out of production. R-404A and R-507A need an oil change to POE.

What is the difference between R-502 and R-404A?

R-502 is a CFC/HCFC azeotrope on mineral oil or alkylbenzene; R-404A is an HFC blend on POE that runs higher pressures on both sides (see the table above), with performance very similar to R-502 according to BITZER.