R-407C PT Chart: How to Actually Read the Pressures
Real R-407C pressure-temperature values, why its two columns sit about 10 °F apart, which one to use for superheat and subcooling, and what that glide means when you charge a converted R-22 system.
On this page
- What are the actual R-407C pressures?
- Why is the gap between the columns so large?
- Which column do you use for superheat and subcooling?
- How is R-407C different from R-22 on the gauges?
- What rules apply to an R-407C system?
- What this means on the job
- Frequently asked questions
- What are normal R-407C pressures?
- How should R-407C be charged?
- What is a good subcooling for R-407C?
- Can I use an R-22 PT chart for R-407C?
- Is R-407C being phased out?
- Do I need a special certification to work on R-407C?
- Sources
At 40 °F saturation, R-407C reads about 63 psig on the vapor (dew) column and 80 psig on the liquid (bubble) column. At 100 °F it reads about 226 psig liquid. R-407C is a zeotropic blend with roughly 10 °F of glide, so the two columns matter: use vapor for superheat, liquid for subcooling.
Most R-407C charts online are a distributor PDF with two columns of numbers and no explanation of why there are two. On R-410A or R-404A you can get away with not knowing, because the columns sit a psi or two apart. On R-407C you cannot. Pick the wrong column and your superheat or subcooling is off by about ten degrees, which is enough to make a correct charge look badly wrong. That matters more than usual because R-407C is the refrigerant most often found in converted R-22 equipment, and the person reading the gauges often still has R-22 numbers in their head.
What are the actual R-407C pressures?
These values come from the Arkema Forane 407C Pressure Temperature Chart, which was generated from the NIST REFPROP database. Pressures are psig.
| Temperature | Liquid (bubble) | Vapor (dew) |
|---|---|---|
| 0 °F (−17.8 °C) | 29.5 psig | 19.4 psig |
| 10 °F (−12.2 °C) | 39.5 psig | 27.9 psig |
| 20 °F (−6.7 °C) | 51.2 psig | 37.9 psig |
| 30 °F (−1.1 °C) | 64.7 psig | 49.6 psig |
| 40 °F (4.4 °C) | 80.2 psig | 63.2 psig |
| 45 °F (7.2 °C) | 88.8 psig | 70.7 psig |
| 50 °F (10.0 °C) | 97.9 psig | 78.8 psig |
| 60 °F (15.6 °C) | 118.0 psig | 96.8 psig |
| 70 °F (21.1 °C) | 140.5 psig | 117.3 psig |
| 80 °F (26.7 °C) | 165.8 psig | 140.5 psig |
| 90 °F (32.2 °C) | 194.1 psig | 166.7 psig |
| 100 °F (37.8 °C) | 225.5 psig | 196.1 psig |
| 110 °F (43.3 °C) | 260.3 psig | 229.0 psig |
| 120 °F (48.9 °C) | 298.6 psig | 265.8 psig |
| 130 °F (54.4 °C) | 340.7 psig | 306.7 psig |
The gap between the columns is 17 psi at 40 °F and nearly 30 psi at 100 °F. That is not a rounding difference; it is the glide showing up in the pressures. Work from the current chart published by the maker of what is in the cylinder, and set your digital manifold to R-407C before you connect it.
Why is the gap between the columns so large?
Because R-407C is a zeotropic blend of R-32, R-125 and R-134a, and those three components boil at different temperatures.
A single-compound refrigerant like R-22 changes state at one temperature for each pressure, so its chart needs only one column. A blend does not. At a given pressure, the bubble point is the temperature where the liquid first starts to boil, and the dew point is where the last of it has vaporized. The spread between the two is the glide.
You can read R-407C's glide straight off the chart. At 40 °F the vapor column shows 63.2 psig. The liquid column hits that same pressure at about 29 °F. So at a normal evaporator pressure, the refrigerant starts boiling around 29 °F and finishes around 40 °F, roughly 11 °F of glide. On the high side it is similar: 225.5 psig is the 100 °F bubble point and roughly the 109 °F dew point.
| Refrigerant | Type | Glide in service | What the chart prints |
|---|---|---|---|
| R-22 | Single compound | None | One column |
| R-410A | Near-azeotrope | Under about 0.3 °F | One column |
| R-404A | Near-azeotrope | About 1 °F | Two columns, 1 to 2 psi apart |
| R-407C | Zeotrope | About 10 °F | Two columns, 17 to 30 psi apart |
That is why the R-410A PT chart gets away with a single column and R-407C cannot.
Which column do you use for superheat and subcooling?
| Calculation | Pressure you read | Chart column | Where you take the temperature |
|---|---|---|---|
| Superheat | Suction | Vapor (dew) | Suction line, at the same point |
| Subcooling | Liquid line | Liquid (bubble) | Liquid line, at the condenser outlet |
The logic is physical. Superheat measures how far the vapor has warmed past the point where the last liquid boiled off, so you compare it to the dew point. Subcooling measures how far the liquid has cooled below the point where it would start to boil, so you compare it to the bubble point.
Here is what the wrong column costs you. Suction reads 63 psig and the suction line is 50 °F. Against the vapor column, saturation is 40 °F and superheat is 10 °F. Against the liquid column, saturation is about 29 °F and superheat looks like 21 °F, which reads as an undercharge. Add refrigerant to "fix" it and you overcharge a system that was right. Superheat and subcooling, and what each reading actually tells you walks through the combinations.
Some equipment manufacturers publish evaporator targets referenced to the midpoint of the glide instead. If the literature for the unit says so, follow it. Otherwise, dew for superheat and bubble for subcooling is the convention.
How is R-407C different from R-22 on the gauges?
R-407C was formulated to match R-22's capacity in air conditioning, and it is listed under EPA's SNAP program as an acceptable R-22 retrofit. The pressures are close but not the same. At 40 °F, R-407C's dew point is 63.2 psig against about 68.6 psig for R-22, so a converted system read against an R-22 chart looks about 5 psi low on the suction side. On the high side it goes the other way: R-407C's bubble point at 100 °F is 225.5 psig, noticeably above R-22 at the same temperature.
The practical traps come from the conversion, not the chart:
- Oil. R-22 runs mineral oil. R-407C needs polyol ester (POE), so a retrofit means an oil change and usually a new drier. What actually works as an R-22 replacement covers this in detail.
- Charging. Because of the glide, charge R-407C as liquid from the cylinder, metered into the suction side so you do not slug the compressor. Charging vapor draws off the lighter components first and changes the blend in both the cylinder and the system. That is manufacturer guidance and good practice, not a Section 608 rule.
- Leaks. A vapor leak from a zeotrope does not lose all three components evenly. After a large leak, the remaining charge may no longer be R-407C in the proportions the chart assumes. Topping it off keeps the error; recovering and recharging removes it.
- Labeling. Check the unit. If someone converted it and did not label it, the only honest answer is to identify the refrigerant before you trust any chart.
What rules apply to an R-407C system?
R-407C is an HFC blend with no ozone-depleting component, and its GWP is about 1,774. That puts it under two different programs.
Section 608. 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-407C 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 air conditioner. The Section 608 leak repair rule at 40 CFR 82.157 does not reach R-407C, because it covers only appliances containing ozone-depleting refrigerant.
The AIM Act. Since January 1, 2026, the leak repair rule at 40 CFR 84.106 covers appliances with 15 pounds or more of a refrigerant containing an HFC. According to EPA's leak repair fact sheet, the thresholds are 10% for comfort cooling, 20% for commercial refrigeration and 30% for industrial process refrigeration. The residential and light commercial air conditioning subsector is exempt, so a converted house system is not covered, but a larger R-407C packaged unit or chiller can be.
New equipment. EPA's Technology Transitions restrictions set a 700 GWP limit for new residential and light commercial air conditioning and heat pump systems from January 1, 2025. R-407C is far above it. None of this stops you servicing or recharging an existing R-407C system; the AIM Act restricts new equipment and supply, not repairs.
What this means on the job
Confirm what is in the system from the label, set the manifold to R-407C, and read suction against the vapor column and liquid against the liquid column. If your superheat looks about ten degrees high, check which column you used before you reach for the cylinder. Charge as liquid, and compare your readings to the equipment manufacturer's targets, not to R-22 habits.
A 500-micron dehydration vacuum after an oil change or repair is good practice, not the Section 608 recovery requirement, and it is worth knowing which is which, because the exam tests the difference. If you are still working toward Type II, the Type II practice test covers the recovery levels and blend rules these systems depend on, and the EPA 608 study guide explains glide and fractionation in exam terms.
Frequently asked questions
What are normal R-407C pressures?
There is no single normal figure, because pressures follow evaporator and condensing temperatures. A coil at 40 °F corresponds to about 63 psig on the vapor column, and a 100 °F condensing temperature to about 226 psig on the liquid column. Convert gauge readings to temperatures and compare superheat and subcooling with the manufacturer's targets.
How should R-407C be charged?
Charge R-407C as liquid from the cylinder, metered slowly into the suction side so liquid does not reach the compressor. Because it is a zeotropic blend, charging vapor removes the components unevenly and changes the composition. After a significant leak, recovering the remaining charge and weighing in a fresh one is the reliable fix.
What is a good subcooling for R-407C?
Use the target on the equipment manufacturer's charging chart or nameplate, since it depends on the metering device and design. Whatever the target, calculate subcooling against the liquid (bubble) column. Using the vapor column on R-407C overstates subcooling by roughly ten degrees, which can hide an undercharge.
Can I use an R-22 PT chart for R-407C?
No. R-407C runs at different pressures from R-22 and has about 10 °F of glide, which R-22 does not. At 40 °F, R-407C's dew point is 63.2 psig against about 68.6 psig for R-22. Reading a converted system against R-22 values makes a correct charge look wrong.
Is R-407C being phased out?
Its production is being reduced under the AIM Act HFC phasedown, and new residential and light commercial air conditioning systems must use refrigerants under 700 GWP from January 1, 2025. R-407C, at about 1,774, cannot be used in those. Servicing existing R-407C equipment remains legal.
Do I need a special certification to work on R-407C?
No. Type II or Universal Section 608 certification covers high-pressure appliances, including R-407C systems, and it does not expire. There is no separate credential for blends. What the exam expects is that you understand glide, liquid charging and recovery levels, which is exactly how R-407C gets tested.
Sources
- Arkema, Forane 407C 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
Notice
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