R-422B (NU-22B) PT Chart and Refrigerant Profile

Where you will find R-422B

R-422B is NU-22B, a blend first sold by ICOR International. Chemours bought ICOR and now sells it as Freon NU-22B. Chemours covers it in the same retrofit guidelines as MO99, for R-22 DX residential and commercial air conditioning and for medium- and low-temperature DX refrigeration.

Expect it in converted R-22 splits, package units and commercial refrigeration; the nameplate still reads R-22, so check the retrofit label. Chemours does not recommend NU-22B for centrifugal compressors or for chillers with flooded evaporators.

The 3% isobutane helps mineral oil return; the blend is A1. In a Chemours calorimeter comparison at AHRI 540 conditions, R-422B ran 12% below R-22 in capacity and 3% in COP, with a 37°F lower discharge temperature; the retrofit guide says capacity and efficiency are similar in most systems.

Charging R-422B

The Chemours procedure for R-22 DX systems:

1. Record baseline R-22 pressures, temperatures, superheat and subcooling.
2. Recover and weigh the R-22. Hold the system under vacuum to pull dissolved R-22 from the oil, then break vacuum with dry nitrogen.
3. Replace the filter-drier with the same type, rated for HFCs.
4. Replace critical elastomeric seals.
5. Evacuate to 500 microns and confirm it holds (evacuation targets).
6. Charge liquid only, starting at about 85% of the R-22 charge weight. The final charge is usually about 95%.
7. Adjust the TXV and charge in small steps until superheat matches what you had on R-22.
8. Monitor the oil level, leak-check again, and label the refrigerant and oil.

As a zeotrope, the cylinder vapor is a different mix from the liquid. Draw liquid only (invert a cylinder without a dip tube), flash it through the manifold if feeding the suction side, and never slug the compressor.

A TXV that was sized correctly for R-22 normally stays; Chemours expects only a slight adjustment for glide and the lower suction pressure. On pistons and cap tubes the charge is critical. Start at 85%, then add toward target superheat. If head pressure rises well above normal R-22 levels before the charge weight is in, stop and look for a restriction. On TXV systems, check subcooling against the equipment data.

Read the dew column for superheat and the bubble column for subcooling. The computed glide is 7.6°F at 40°F dew and 5.3°F at 100°F bubble. Suction runs lower than R-22: 59.4 psig dew at 40°F versus 68.6 psig. On the high side, the bubble pressure at 100°F is 198.9 psig versus 195.9 for R-22. Some sight-glass bubbles are normal with these blends, so do not charge to a clear glass.

Systems already on NU-22B can be topped off with NU-22B, but Chemours says to pull the whole charge on critically charged systems, as with R-22.

Oil and compatibility

Chemours says NU-22B works with the existing mineral oil or alkylbenzene in most systems. POE may be needed where oil return is poor. BITZER’s data table lists POE only, so check the compressor maker’s approval before relying on mineral oil in a semi-hermetic.

Chemours adds POE (about 20% of the total oil charge, then small increments) in these cases:

• the oil level falls steadily or swings during a cycle
• the system has a liquid receiver but no oil separator
• the piping is complex, or the evaporator sits well below the condensing unit
• the heat exchangers use enhanced tubes and circulate a lot of oil

Keep the oil below mid-glass right after adding it, or drain an equal amount of mineral oil first. Trane 3-D and Danfoss SM scrolls need a one-time sump change to OEM-approved POE. Screw compressors should be switched to POE while still running on R-22. See the refrigerant oil guide.

R-22 swells elastomers more than HFCs do, so a seal that held on R-22 can leak once the HFC is in. Replace Schrader cores and any seal that needs the charge removed to change, and check solenoid valves, ball valve stems, receiver gaskets and flanges after start-up.

Safety, handling and recovery

R-422B is A1 (lower toxicity, no flame propagation). It is a Section 608 high-pressure refrigerant, so you need Type II or Universal certification. Since Jan 1 2018, its sale has been restricted to certified technicians, and venting it is prohibited.

Required recovery levels for high-pressure appliances made after Nov 15 1993:

• under 200 lb charge: 0 in Hg
• 200 lb or more: 10 in Hg

Most R-22 recovery machines can be used, avoiding cross-contamination. Use an electronic HFC leak detector, and never leak-check with air and refrigerant mixtures.

New cylinders made since Jan 1 2020 are light green-gray (RAL 7044) under AHRI Guideline N, with no red band because the blend is not flammable. We have not verified a legacy paint color for R-422B, so go by the label (cylinder colors).

Status and replacements

EPA SNAP lists R-422B as acceptable for replacing R-22 in residential and light commercial AC (Mar 29 2006). Its AR4 GWP of about 2,526 is above the 700 limit that has applied to new residential and light commercial AC and heat pumps since Jan 1 2025 (40 CFR 84.54), so it is a retrofit and service refrigerant only. AIM Act allowances are 60% of the HFC baseline in 2024–2028, 30% in 2029–2033, 20% in 2034–2035 and 15% from 2036.

Other mineral-oil retrofit options are covered in R-22 replacement options and R-22 vs MO99.

Common questions

What is the difference between R-422B and R-422D?

Both are R-125, R-134a and isobutane blends. R-422D carries more R-125 (65.1% vs 55%), which gives it higher suction pressure: 66.5 psig dew at 40°F versus 59.4 for R-422B. The two are not interchangeable on one PT chart.

Can R-422B be mixed with R-22 or MO99?

No. Chemours says not to mix NU-22B and MO99 in the same system, and not to top off R-22 with any other refrigerant. Recover the R-22 first.