R-448A PT Chart: How to Actually Read the Pressures

At −20 °F, R-448A reads about 10 psig on the vapor column and 17 psig on the liquid column. At 40 °F it reads about 72 psig (vapor) and 89 psig (liquid), and at 100 °F about 244 psig (liquid). R-448A is a zeotropic blend with a wide glide. Use the vapor column for superheat and the liquid column for subcooling.

R-448A (Honeywell sells it as Solstice N40) is one of the refrigerants that has quietly taken over from R-404A in walk-ins, reach-ins and supermarket racks. It moves differently on the gauges. The two columns on its chart sit roughly 10 °F apart, not the 1 °F you get on R-404A. A technician who reads the wrong column on an R-448A freezer can be off by 10 °F on superheat and misdiagnose a system that is working fine.

What are the actual R-448A pressures?

These values come from Arkema's Forane Refrigerants Pressure Temperature Chart, which lists R-448A liquid and vapor pressures side by side. All pressures are in psig.

Temperature	Liquid (bubble)	Vapor (dew)
−30 °F (−34.4 °C)	10.4 psig	4.4 psig
−20 °F (−28.9 °C)	17.0 psig	9.8 psig
−10 °F (−23.3 °C)	24.9 psig	16.4 psig
0 °F (−17.8 °C)	34.2 psig	24.3 psig
10 °F (−12.2 °C)	45.1 psig	33.6 psig
20 °F (−6.7 °C)	57.8 psig	44.6 psig
30 °F (−1.1 °C)	72.3 psig	57.3 psig
40 °F (4.4 °C)	89.0 psig	72.1 psig
50 °F (10.0 °C)	108.0 psig	89.0 psig
70 °F (21.1 °C)	153.5 psig	130.3 psig
90 °F (32.2 °C)	210.5 psig	183.0 psig
100 °F (37.8 °C)	243.7 psig	214.3 psig
110 °F (43.3 °C)	280.5 psig	249.2 psig
120 °F (48.9 °C)	320.9 psig	288.1 psig

For comparison, R-404A at 40 °F reads about 87 psig liquid and 85 psig vapor on the same chart. The liquid side of R-448A is close to R-404A. The vapor side is well below it. That gap is the whole story of this refrigerant on the gauges.

Set your digital manifold to R-448A before you connect, and check the unit label. R-449A looks similar on paper but its values are not identical, and a system retrofitted from R-404A may still carry the old nameplate.

Why are the two columns so far apart?

Because R-448A has a large temperature glide.

R-448A is a blend of five refrigerants: R-32, R-125, R-134a, R-1234yf and R-1234ze. Those components boil at different temperatures, so the blend does not change state at one point. When you hold the pressure steady, the bubble point (where liquid starts to boil) sits several degrees below the dew point (where the last liquid has vaporized).

You can read the glide straight off the chart. At 72 psig, the vapor column says 40 °F, while the liquid column reaches about 72 psig at 30 °F. That is roughly 10 °F of glide at evaporator pressures. R-404A, by contrast, glides about 1 °F. The R-404A PT chart shows the two columns almost touching.

In practice, the refrigerant in an R-448A evaporator is colder at the inlet than at the outlet even with no pressure drop. Frost patterns and coil temperatures look different from R-404A, and that is normal.

Which column do you use for superheat and subcooling?

Calculation	Pressure you read	Chart column	Where you take the temperature
Superheat	Suction, at the evaporator outlet or service port	Vapor (dew)	Suction line, at the same point
Subcooling	Liquid line	Liquid (bubble)	Liquid line, at the condenser or receiver outlet

The reasoning is physical. Superheat is how far the vapor has warmed past the point where the last drop of liquid boiled off, so you compare against the dew point. Subcooling is how far the liquid has cooled below the point where it would start to boil, so you compare against the bubble point.

Here is what the wrong column costs you. Say suction reads 24 psig and the suction line is 10 °F. On the vapor column, 24 psig is about 0 °F, so superheat is 10 °F. Read the liquid column by mistake and 24 psig is about −10 °F, so you'd calculate 20 °F of superheat and go chasing a starved evaporator that isn't starved.

Some equipment makers publish evaporator ratings at a mean or mid-point temperature instead of the dew point. That affects how you compare coil temperature with the design sheet. It does not change how you calculate superheat. Superheat and subcooling, and what each reading actually tells you walks through the combinations.

What are normal R-448A running pressures on a freezer?

No single number is correct, and any chart that prints one is assuming a design you may not have.

Suction pressure follows evaporator coil temperature, which the manufacturer designs to sit some degrees below box temperature. As an illustration only: a freezer evaporator designed to run at −20 °F should read near 10 psig on the vapor column. A medium-temperature cooler with a 20 °F coil should read near 45 psig. Those are much lower than the R-404A figures a technician may have memorized (about 16 and 55 psig). A low suction reading on an R-448A retrofit is not automatically a low charge.

Head pressure works the same way. The liquid-line reading maps to a condensing temperature on the liquid column. That temperature sits above the air or water the condenser rejects heat into, so a rooftop unit on a 95 °F day and one in a cool machine room read very differently and can both be right.

Can you charge R-448A as vapor?

No. Charge it as liquid. Because R-448A is a zeotropic blend, its components evaporate at different rates. Drawing vapor off the top of the cylinder pulls more of the lighter components and leaves the rest behind, which shifts the composition of what goes into the system. Removing it from the cylinder as liquid keeps the blend at its rated makeup. Meter the liquid carefully on the suction side so you don't slug the compressor.

The same fractionation is why a leaking R-448A system should not just be topped off repeatedly. Find the leak first.

What rules apply to an R-448A system?

Section 608 leak repair does not. The rule at 40 CFR 82.157 covers appliances with 50 pounds or more of an ozone-depleting refrigerant (CFCs and HCFCs such as R-22). R-448A contains no ozone-depleting component.

The AIM Act leak repair rule does. Since January 1, 2026, 40 CFR 84.106 covers appliances holding 15 pounds or more of a refrigerant containing an HFC, per EPA's leak repair fact sheet. R-448A is about 73% HFC by weight, so a typical walk-in or rack qualifies. The fact sheet sets a 20% leak rate threshold for commercial refrigeration and a 30-day repair deadline.

The rest of Section 608 applies in full. You may not knowingly vent R-448A (40 CFR 82.154), and you must recover it to the required level before opening the system (40 CFR 82.156). R-448A equipment is high-pressure, so it is Type II work. For a high-pressure appliance under 200 pounds, recovered with equipment manufactured on or after November 15, 1993, the required level is 0 inches of mercury. That date refers to the recovery machine, not the freezer. A 500-micron dehydration vacuum before charging is good service practice, not the Section 608 recovery requirement.

New equipment. Manufacturers list R-448A at a GWP of about 1,387. EPA's Technology Transitions restrictions by sector set an initial 1,400 GWP limit for new remote condensing units (from July 27, 2026) and new supermarket systems (from January 1, 2027), a 700 limit for new cold storage warehouses (from July 27, 2026), and 150 for new stand-alone retail units. R-448A clears the first limit narrowly and fails the other two. Final limits of 150 or 300 arrive January 1, 2032. None of this restricts servicing an existing system. Check the EPA page for your subsector, since these dates have been revised before.

What this means on the job

Set the manifold to R-448A. Read suction against the vapor column and liquid against the liquid column, and expect suction to look low if R-404A numbers are still in your head. Charge liquid, not vapor. Compare superheat and subcooling to the manufacturer's targets.

When you add refrigerant to a system holding 15 pounds or more, record how much, which refrigerant, the date and the appliance, and give it to the owner. Their federal leak rate calculation runs on that record. If you are still working toward your card, the Type II practice test covers the recovery levels and leak rates these systems depend on.

Frequently asked questions

What is the normal suction pressure for R-448A?

It depends on the design coil temperature. On the vapor column, a −20 °F freezer coil corresponds to about 10 psig and a 20 °F cooler coil to about 45 psig. Convert the reading to a temperature, calculate superheat, and compare it with the equipment maker's target. Don't judge it against remembered R-404A numbers.

Which column of the R-448A chart do I use?

Use the vapor, or dew point, column for superheat from suction pressure. Use the liquid, or bubble point, column for subcooling from liquid-line pressure. On R-448A the two differ by roughly 10 °F at evaporator pressures, so using the wrong column can make a correctly fed evaporator look starved.

What is R-448A pressure at 70 °F?

About 153.5 psig on the liquid column and 130.3 psig on the vapor column, per Arkema's chart. A system at rest in a 70 °F room with liquid refrigerant present should read somewhere in that range, usually nearer the liquid figure. A standing reading far below it can point to a low charge, but it is not proof.

Is R-448A a drop-in replacement for R-404A?

It is widely used to retrofit R-404A systems, but it is not a pure drop-in. The glide changes how you read pressures and set superheat, and expansion valves, controls and oil may need attention. Follow the refrigerant and equipment makers' retrofit guidelines and relabel the system with the new refrigerant when you finish.

Is R-448A being phased out?

Not for servicing. It contains HFCs, so its supply falls under the AIM Act phasedown, and new-equipment GWP limits already rule it out for stand-alone retail units and cold storage warehouses. Existing R-448A systems can be repaired and recharged, and the AIM Act leak repair rule applies at 15 pounds and up.

Do I need a special certification to work on R-448A?

No. A Type II or Universal Section 608 certification covers high-pressure appliances, including R-448A systems, and it does not expire. R-448A is classed A1, nonflammable, so the extra A2L handling steps don't apply. What has changed is the service paperwork owners need under the AIM Act leak repair rule.

Sources

• Arkema, Forane Refrigerants Pressure Temperature Chart
• Honeywell, Solstice N40 (R-448A) physical properties
• EPA, Leak Repair Requirements for Appliances Containing HFCs and Certain Substitutes (fact sheet, January 2026)
• 40 CFR 84.106 — Leak repair
• 40 CFR 82.157 — Appliance maintenance and leak repair
• 40 CFR 82.154 — Prohibitions
• 40 CFR 82.156 — Proper evacuation of refrigerant from appliances
• EPA, Technology Transitions HFC Restrictions by Sector