R-421A PT Chart and Refrigerant Profile

Where you will find R-421A

R-421A is an R-22 service blend. You find it in R-22 air conditioners, heat pumps and medium- or high-temperature refrigeration that were recharged with it instead of R-22, not in equipment designed for it. A-Gas sells it as Choice R421A and lists residential and commercial AC and commercial and industrial refrigeration as uses, with performance temperature ranges comparable with R-22 (A-Gas).

The nameplate on these systems still says R-22, so the retrofit label is your only clue. If there is no label and the pressures do not match R-22 at the measured temperatures, assume an unknown blend and recover it rather than topping off.

R-421A is a two-part HFC blend of R-125 and R-134a (58/42 by mass). It contains no R-22 and no ozone-depleting component. New cylinders are light green-gray (RAL 7044) like every refrigerant, so go by the label.

Charging R-421A

Charge liquid only. R-421A is a zeotropic blend, and vapor drawn from the cylinder does not have the same composition as the liquid. Meter the liquid into the suction side slowly with the system running.

R-421A does not read like R-22 on the gauges. At 40°F, R-22 saturates at 68.6 psig. R-421A at 40°F shows 58.1 psig on the dew column and 68.7 psig on the bubble column, a glide of about 7.6°F. If you read an R-421A system with an R-22 scale, the suction saturation temperature comes out wrong and so does superheat. Set your manifold or digital gauge to R-421A, or use the gauge lookup on this page.

• Superheat: convert suction pressure with the dew column. On fixed-orifice systems, charge to target superheat from CEC Title 24 Table RA3.2-2 (installer tolerance ±5°F, valid at 55–115°F outdoor, return dry bulb of 70°F or more, return wet bulb of 76°F or less) with the target superheat calculator.
• Subcooling: convert liquid-line pressure with the bubble column, then compare it with the manufacturer’s subcooling target for TXV systems using the subcooling calculator.

The temperature glide calculator gives the glide at any pressure. A-Gas’s product page gives no starting charge percentage, so add charge by weight in small steps and finish to superheat or subcooling. The OEM targets were set for R-22 and the blend supplier’s retrofit instructions take precedence.

Do not top off an R-22 system with R-421A or mix the two. Recover all R-22 first, then charge R-421A into the evacuated system.

Oil and compatibility

Sources differ on oil. A-Gas lists R-421A as compatible with mineral oil (MO), alkylbenzene (AB) and POE (A-Gas), which is why it is sold as a retrofit that can keep the existing oil. BITZER’s refrigerant data table lists POE only for R-421A (BITZER).

In practice, check the compressor maker’s approval for R-421A with the oil already in the system. Replace the filter-drier, label the system with the refrigerant and oil, and evacuate to the OEM target, typically 350–500 microns (evacuation guide). See the refrigerant oil guide.

Safety, handling and recovery

R-421A is ASHRAE class A1: lower toxicity and no flame propagation. It runs in the same pressure range as R-22, so R-22-rated gauges, hoses and recovery cylinders are suitable.

Section 608 Type II (or Universal) certification covers R-421A systems, and since Jan 1 2018 only certified technicians may buy it. By the 40 CFR 82.152 definition it is a high-pressure refrigerant: its computed liquid saturation pressure at 104°F is 224.1 psia (209.4 psig, bubble). Recover appliances under 200 lb to 0 in Hg, and those of 200 lb or more to 10 in Hg.

Recover R-421A into its own labeled recovery cylinder (gray with a yellow top), never into a tank that already holds R-22 or another blend.

Status and replacements

EPA’s SNAP program listed R-421A as an acceptable R-22 substitute in residential and light commercial AC on Sept 28 2006 (EPA SNAP). Using it to service and retrofit existing R-22 systems remains legal.

It is all HFC, with a GWP of 2,631 (AR4), higher than both R-22 (1,810) and R-410A (2,088). That has two consequences:

• Supply: every pound counts against the AIM Act HFC phasedown, which steps allowances down to 60% of baseline in 2024–2028, 30% in 2029–2033, 20% in 2034–2035 and 15% from 2036.
• New equipment: under the Technology Transitions rule (40 CFR 84.54) its GWP is far above the limits for new AC, heat pumps and commercial refrigeration. R-421A is also named as restricted in new road and marine transport refrigeration from Jan 1 2025.

For a long-term fix, replacing the R-22 equipment is the alternative to a retrofit. Other R-22 retrofit blends include R-422B, R-422D, R-438A, R-427A, R-417A and R-407C. Compare them in R-22 replacement refrigerants, and see the R-22 phase-out guide.

Common questions

Is R-421A a drop-in replacement for R-22?

It is sold as one that can run with the existing oil (A-Gas), but it is not identical to R-22. Its dew-point pressures are lower than R-22’s at the same temperature, it has glide, and it must be charged as liquid.

What oil does R-421A use?

A-Gas lists mineral oil, AB and POE as compatible; BITZER lists POE. Confirm with the compressor maker.