R-401B PT Chart and Refrigerant Profile

Where you will find R-401B

R-401B is the low-temperature sister of R-401A. Both are HCFC service blends of R-22, R-152a and R-124, sold by DuPont as Suva MP66 and MP39 (now Chemours; R-401B is sold as Freon MP66). R-401B carries more R-22, which raises its capacity. DuPont’s ART-36 retrofit guide places it in R-12 systems running at low evaporator temperatures (below about -15°F) that need extra capacity, and in existing R-500 systems.

In practice that means domestic and commercial freezers and transport refrigeration. EPA’s SNAP program listed it as an R-12 substitute on Jan 13 1995 across household refrigerators and freezers, ice machines, supermarket and stand-alone equipment, vending, cold storage and transport. Copeland lists it for low- and medium-temperature work “for service applications only”.

Look for a retrofit tag reading R-401B or MP66 on a system whose compressor and nameplate say R-12 or R-500. The legacy cylinder color assigned in AHRI Guideline N-2017 was yellow-brown (mustard). Containers made since 2020 are light green-gray for every refrigerant, so read the label. R-401A and R-401B share components but not proportions, and their PT tables differ.

Charging R-401B

R-401B is a zeotropic blend. The computed glide at 40°F evaporating is 9.6°F, and it shrinks a little as pressure rises.

Charge liquid only. ART-36 says to take liquid only from the cylinder. Vapor charging pulls the lighter components first and leaves the system and the cylinder off-blend. Meter the liquid in slowly so it flashes before reaching the compressor.

Size the charge per the retrofit guide. ART-36 puts the best charge for an R-12 conversion at usually 75-90% of the original R-12 charge by weight, starting at about 75%. An R-500 conversion needs about 105% of the R-500 charge, starting at 100%. ART-36 does not recommend topping off a CFC system with Suva. Chemours’ MP66 bulletin says a system already on MP66 can be topped off after a leak, as long as you charge liquid.

Read the right column. Use the dew (vapor) column for superheat at suction pressure and the bubble (liquid) column for subcooling at liquid-line pressure. The superheat calculator uses the dew column; the temperature glide calculator shows the gap at any pressure. On a TXV system, charge by subcooling to the equipment or retrofit target with the subcooling calculator.

Expect the high side to run well above R-12. On this site’s tables, R-401B reads 39.8 psig at a 40°F dew point against 36.9 psig for R-12 at 40°F. At a 100°F bubble point it reads 152.0 psig against 116.9 psig for R-12. Do not charge to R-12 pressures.

Oil and compatibility

Sources differ on oil, so follow the compressor manufacturer:

• BITZER lists mineral oil and alkylbenzene.
• Chemours’ MP66 bulletin says it works with mineral oil and AB and needs no oil change on retrofit.
• Copeland lists AB with mineral oil, or POE-32.
• ART-36 says AB or POE can be used and existing mineral oil works in many close-coupled systems. For best oil return it suggests one oil change from mineral oil to AB, which removes 50-80% of the mineral oil.

Do not mix R-401B with R-12, R-500, R-401A or anything else. A mixture matches no PT chart. The refrigerant oil types guide compares the lubricants.

Safety, handling and recovery

R-401B is A1: lower toxicity, no flame propagation. It is an ozone-depleting refrigerant (ODP 0.040 from the 40 CFR 82 values for HCFC-22 and HCFC-124). Knowingly venting it is prohibited, recovery is required, and sales are restricted to certified technicians.

40 CFR 82.152 does not name R-401B, so its class comes from the 104°F liquid saturation pressure. This site’s table gives 161.5 psig (176.2 psia) at 104°F bubble, just over the 170 psia line, which makes it a high-pressure refrigerant by the definition. Small appliances (factory-sealed, 5 lb or less) need Type I certification, other equipment Type II; Universal covers both.

Appliances with 50 lb or more fall under the ODS leak-repair rules in 40 CFR 82.157. Recovered R-401B cannot be sold to a new owner unless an EPA-certified reclaimer has reclaimed it.

Status and replacements

R-401B is regulated through its HCFCs. Since Jan 1 2010, HCFC-22 may be used as a refrigerant only in equipment made before that date, and its production and import ended Jan 1 2020. Since Jan 1 2020, newly produced HCFC-124 may be used only in equipment made before 2020, and HCFC-124 allowances fall to zero in 2030 (40 CFR 82.15). Supply is recovered, reclaimed or older stock.

No manufacturer or EPA document found names a dedicated successor for R-401B. Two HFC-based products list it among the refrigerants they replace:

• R-437A (Freon MO49 Plus), which Chemours lists for R-12, R-401A, R-401B and R-409A systems.
• R-450A (Solstice N13), which Honeywell’s application guide lists for R-401A, R-401B and R-409A.

Neither was designed for R-401B’s low-temperature niche, so confirm capacity and compressor approval first. The R-134a replacement guide covers the wider HFC and HFO options.

Common questions

What is the difference between R-401A and R-401B?

Same three components, different proportions. R-401B has 61% R-22 against 53% in R-401A, giving more capacity at low evaporator temperatures. DuPont aimed R-401B at low-temperature R-12 equipment and R-500 systems, and R-401A at general R-12 refrigeration.