R-404A PT Chart: How to Actually Read the Pressures

At −20 °F saturation, R-404A reads about 16 psig (vapor); at 40 °F, about 85 psig; at 100 °F, about 237 psig (liquid). R-404A is a near-azeotropic blend with a small glide, so its chart prints two columns that sit only 1 to 2 psi apart. Use the vapor column for superheat and the liquid column for subcooling.

R-404A is the refrigerant in a huge share of the walk-in freezers, reach-in coolers and supermarket cases still running in the US, and most of the PT charts for it online are a distributor PDF with nothing attached. That is fine if you already know what the numbers are for. It is not fine when a freezer is sitting at 20 psig suction and you are trying to decide whether that is a problem. It is also the refrigerant where the law has quietly changed underneath technicians: the leak repair rules that apply to an R-404A system in 2026 are not the Section 608 ones most people learned.

What are the actual R-404A pressures?

These values come from the Arkema Forane 404A Pressure Temperature Chart, which was generated from the NIST REFPROP database. Pressures are psig.

Temperature	Liquid (bubble)	Vapor (dew)
−40 °F (−40.0 °C)	4.9 psig	4.3 psig
−30 °F (−34.4 °C)	10.3 psig	9.6 psig
−20 °F (−28.9 °C)	16.8 psig	16.0 psig
−10 °F (−23.3 °C)	24.6 psig	23.6 psig
0 °F (−17.8 °C)	33.7 psig	32.6 psig
10 °F (−12.2 °C)	44.3 psig	43.1 psig
20 °F (−6.7 °C)	56.6 psig	55.3 psig
30 °F (−1.1 °C)	70.7 psig	69.3 psig
40 °F (4.4 °C)	86.9 psig	85.4 psig
50 °F (10.0 °C)	105.3 psig	103.6 psig
70 °F (21.1 °C)	149.3 psig	147.4 psig
90 °F (32.2 °C)	204.5 psig	202.4 psig
100 °F (37.8 °C)	236.8 psig	234.6 psig
110 °F (43.3 °C)	272.5 psig	270.4 psig
120 °F (48.9 °C)	312.1 psig	309.9 psig

For orientation: R-404A runs well below R-410A (about 118 psig at 40 °F) and well above R-22 (about 69 psig). Work from the current chart published by the maker of what is in the cylinder, and set your digital manifold to R-404A before you connect it. If the system has been retrofitted to R-448A or R-449A, this chart is the wrong one — check the label on the unit.

Why does an R-404A chart have two columns?

Because R-404A is a blend, and blends have temperature glide.

R-404A is a mixture of R-125, R-143a and R-134a. Those components boil at slightly different temperatures, so the blend does not change state at a single point. The bubble point (liquid column) is where liquid first starts to boil; the dew point (vapor column) is where the last liquid has vaporized.

R-404A is classed as near-azeotropic: its glide is small but not zero. You can read it straight off the chart. At 40 °F the vapor column says 85.4 psig; the liquid column reaches that same pressure at about 39 °F. That is roughly 1 °F of glide — more than R-410A, far less than a true zeotrope like R-407C or R-454B, whose chart gaps are much wider.

On a medium-temperature cooler, 1 °F rarely changes a decision. On a low-temperature freezer where the superheat target may only be a few degrees, it can. Pick the right column and the question goes away.

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

Most R-404A refrigeration runs on a TXV or EEV, so evaporator superheat is how you check feed. Superheat and subcooling, and what each reading actually tells you walks through the combinations.

What should suction pressure be on an R-404A freezer?

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

Suction pressure follows evaporator coil temperature, and coil temperature sits below the box temperature by a design difference set by the equipment manufacturer. So the question to answer first is: what coil temperature is this system designed for?

As an illustration only: if a freezer's evaporator is designed to run at about −20 °F, the chart says a suction reading near 16 psig is consistent with that. If the same system shows 30 psig, the coil is running around −5 °F, and you look for why — high load, a door left open, a defrost that just ended, or a feed problem. The chart converted the gauge reading into a temperature; the diagnosis still comes from comparing that temperature, and the superheat, against design.

Head pressure works the same way. Discharge or liquid pressure maps to a condensing temperature, and condensing temperature sits above the air or water it rejects heat into. A condenser on a 95 °F roof and one in a 70 °F machine room will read very differently and both be correct.

Does Section 608 leak repair apply to an R-404A system?

This is the part most competitors get wrong, and the answer has two halves.

Under Section 608, no. The leak repair rule at 40 CFR 82.157 applies only to appliances with 50 pounds or more of a Class I or Class II refrigerant (CFCs and HCFCs such as R-22), or a blend containing one. It expressly does not apply to appliances containing solely substitute refrigerants. R-404A is an HFC blend with no ozone-depleting component, so the 608 leak repair rule does not reach it.

Under the AIM Act, yes, since January 1, 2026. EPA's 2024 Emissions Reduction and Reclamation rule set up a separate leak repair program at 40 CFR 84.106. According to EPA's leak repair fact sheet, it covers appliances with a charge of 15 pounds or more of a refrigerant containing an HFC, or a substitute with a GWP above 53. R-404A qualifies.

	Section 608 (40 CFR 82.157)	AIM Act (40 CFR 84.106)
Refrigerants covered	CFCs and HCFCs, or blends containing them	HFCs, and substitutes with GWP above 53
Charge threshold	50 lb or more	15 lb or more
R-404A walk-in with 30 lb	Not covered	Covered
Commercial refrigeration leak rate	20%	20%
Repair deadline	30 days	30 days
Residential and light commercial AC	Covered at 50 lb or more	Exempt

The thresholds and deadlines match, which is exactly why the switch is easy to miss. The difference is the charge size: a mid-sized R-404A walk-in that was never subject to a mandatory leak rate calculation now may be. The duties fall on the owner or operator, but the owner cannot calculate a leak rate without your service records showing how much you added.

The rest of Section 608 still applies to R-404A in full. You may not knowingly vent it (40 CFR 82.154), and you must recover it to the required level before opening the system (40 CFR 82.156). R-404A equipment is high-pressure, which makes it 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 practice, not the Section 608 recovery requirement.

Can you still install new R-404A equipment?

For most new retail food refrigeration, no. R-404A has a GWP of about 3,922. EPA's Technology Transitions restrictions by sector set a 150 GWP limit for new stand-alone retail food units from January 1, 2025, and interim limits of 1,400 for remote condensing units and supermarket systems and 700 for cold storage warehouses. R-404A is far above all of them. EPA revised some of these dates in 2025 and 2026, so check that page for the current compliance date in your subsector. None of this stops you servicing an existing R-404A system; the AIM Act restricts new equipment, not repairs.

What this means on the job

Set the manifold to R-404A, or to whatever the unit label says if it has been retrofitted. Read suction against the vapor column and liquid against the liquid column. Compare superheat and subcooling to the manufacturer's targets, not to a number from a forum.

When you add refrigerant to a system holding 15 pounds or more, write down how much, what, when and on which appliance, and give it to the owner. That record is now what their federal leak rate calculation runs on. If the system is leaking, find the leak before you top it off. And if you are still working toward Type II, the Type II practice test covers the recovery levels and leak rates these systems lean on.

Frequently asked questions

What is the normal suction pressure for an R-404A freezer?

There is no universal figure. Suction pressure reflects the evaporator coil temperature, which the manufacturer designs to sit some degrees below box temperature. A coil at −20 °F corresponds to about 16 psig on the vapor column. Judge the reading by converting it to temperature and comparing superheat with the design target.

Which column of the R-404A chart do I use?

Use the vapor, or dew point, column when calculating superheat from suction pressure. Use the liquid, or bubble point, column when calculating subcooling from liquid-line pressure. On R-404A the two columns are only 1 to 2 psi apart, but on a low-temperature freezer with a tight superheat target the difference can matter.

What is R-404A pressure at 70 °F?

About 149 psig on the liquid column and 147 psig on the vapor column, per the Arkema chart. That is roughly what a system at rest in a 70 °F room shows once pressures equalize, provided liquid refrigerant is present. A standing reading well below that suggests the charge may be low, but it is not proof.

Is R-404A being phased out?

Its production is being cut under the AIM Act HFC phasedown, and new equipment in most retail food refrigeration subsectors can no longer use it. It is not banned for servicing. Existing R-404A systems can be repaired and recharged, though supply will tighten and prices will likely rise as allowances fall.

Does R-404A require leak repair?

Not under Section 608, which only covers CFC and HCFC systems. Since January 1, 2026, the AIM Act leak repair rule at 40 CFR 84.106 covers R-404A appliances with 15 pounds or more of charge, with a 20 percent threshold for commercial refrigeration and a 30-day repair deadline.

Do I need a special certification to work on R-404A?

No. A Type II or Universal Section 608 certification covers high-pressure appliances including R-404A systems, and it does not expire. What changes with R-404A is the paperwork you give the owner under the AIM Act leak repair rule, not the credential you hold.

Sources

• Arkema, Forane 404A Pressure Temperature Chart
• 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