R-410A PT Chart: How to Actually Read the Pressures
Real R-410A pressure-temperature values, why the chart prints one saturation column when an R-454B chart prints two, and why a gauge reading on its own tells you almost nothing about the charge.
On this page
- What are the actual R-410A pressures?
- Why does an R-410A chart print one column when an R-454B chart prints two?
- Which reading do you use for superheat and subcooling?
- What is a good pressure for R-410A?
- Do the pressures change what Section 608 requires?
- What this means on the job
- Frequently asked questions
- How do you use a PT chart for R-410A?
- What is a good low-side pressure for R-410A?
- Why are R-410A pressures so much higher than R-22?
- Does R-410A have temperature glide?
- Can I use an R-410A chart for R-454B?
- Is taking a PT reading required by EPA Section 608?
- Sources
At 40 °F saturation, R-410A reads about 118 psig; at 100 °F saturation, about 319 psig. Because R-410A is a near-azeotropic blend with almost no temperature glide, its PT chart prints one saturation value per temperature rather than two. Use suction pressure for superheat and liquid-line pressure for subcooling — the same number serves both.
Most R-410A PT charts you will find online are a scan of a distributor's PDF with nothing attached but a logo. That is enough if you already know what the numbers are for. It is not enough if you are trying to work out why your gauges say 135 psig on a 95-degree afternoon and whether that means anything at all. A pressure reading is an input to a calculation, not a diagnosis, and treating it as a diagnosis is how good systems get overcharged.
What are the actual R-410A pressures?
These come from the Chemours Pressure-Temperature Guide for A/C, document OPTXLPTAC-2, which lists Freon 410A alongside R-22, R-407C and the A2L replacements on one sheet. R-22 is shown here for comparison because most technicians still carry its numbers in their head.
| Temperature | R-410A | R-22 |
|---|---|---|
| −20 °F | 26.2 psig | 10.2 psig |
| −10 °F | 36.3 psig | 16.5 psig |
| 0 °F | 48.2 psig | 24.0 psig |
| 10 °F | 62.2 psig | 32.8 psig |
| 20 °F | 78.4 psig | 43.1 psig |
| 30 °F | 97.0 psig | 55.0 psig |
| 40 °F | 118.4 psig | 68.6 psig |
| 50 °F | 142.6 psig | 84.1 psig |
| 60 °F | 170.7 psig | 101.6 psig |
| 70 °F | 201.8 psig | 121.4 psig |
| 80 °F | 236.5 psig | 143.6 psig |
| 90 °F | 275.4 psig | 168.4 psig |
| 100 °F | 318.5 psig | 195.9 psig |
| 110 °F | 366.4 psig | 226.4 psig |
| 120 °F | 419.4 psig | 260.0 psig |
R-410A runs roughly 60 to 65 percent higher than R-22 across the range. That is the single most useful thing to know if you came up on R-22 equipment: an R-410A system sitting at 118 psig suction is not high, it is a 40-degree coil.
Work from the current chart published by the manufacturer of what is actually in the cylinder, and set your digital manifold or phone app to R-410A before you connect it.
Why does an R-410A chart print one column when an R-454B chart prints two?
Because of temperature glide, and R-410A has almost none.
A zeotropic blend is made of components that boil at different temperatures, so the mixture does not change state at one fixed point. It changes across a range. The bubble point is where liquid first starts to boil; the dew point is where the last of it has vaporized. The spread between them is glide.
R-410A is a 50/50 blend of R-32 and R-125, and those two happen to sit close enough together that the mixture behaves almost like a single substance. It is classed as near-azeotropic, and its glide is commonly cited at under about 0.3 °F — small enough that correcting for it would be lost in the accuracy of your thermometer. That is why field charts give R-410A a single column.
You can see the effect on the Chemours sheet itself. It switches from printing saturated-vapor values to saturated-liquid values at 52 °F. R-407C, a true zeotrope, jumps from 78.8 psig at 50 °F to 101.7 psig at 52 °F where the column changes. R-410A runs straight through — 142.6 psig at 50 °F, 148.4 psig at 52 °F — because for R-410A the two values are effectively the same number.
This is the habit that stops transferring when the equipment changes. An R-454B chart gives you two saturation values and expects you to pick the right one, and as R-410A is phased down that becomes the normal case rather than the exception.
Which reading do you use for superheat and subcooling?
On R-410A the chart value is the same either way, but the pressure you read is not:
| Calculation | Pressure you read | Where you take the temperature |
|---|---|---|
| Superheat | Suction line, at the service port | Suction line, near the same point |
| Subcooling | Liquid line | Liquid line, at the condenser outlet |
Superheat is the actual suction-line temperature minus the saturation temperature you looked up from suction pressure. Subcooling is the saturation temperature you looked up from liquid-line pressure minus the actual liquid-line temperature. Both are differences, and that is the point — neither one is a pressure.
Which of the two you charge by depends on the metering device, not on preference. A fixed-orifice system is charged by superheat; a TXV or EEV system is charged by subcooling. Superheat and subcooling, and what each reading actually tells you works through the combinations in more detail.
What is a good pressure for R-410A?
There is no such number, and every answer that gives you one is guessing on your behalf.
Saturation pressure follows coil temperature, and coil temperature follows load, airflow, ambient temperature and indoor humidity. The same correctly charged system will read very differently on a 75-degree morning and a 100-degree afternoon. Rules of thumb like "118 on the low side" only hold at one specific set of conditions and quietly mislead everywhere else.
What the chart is actually for:
- Read suction pressure and liquid-line pressure.
- Convert each to a saturation temperature with the chart.
- Measure the actual line temperatures.
- Calculate superheat and subcooling.
- Compare those against the targets printed in the installation instructions for that specific unit.
Step 5 is the one people skip. The target superheat or subcooling comes from the manufacturer, not from the chart and not from the internet.
Do the pressures change what Section 608 requires?
No. Nothing about pressure readings, superheat targets or charging technique appears in 40 CFR Part 82. Taking a PT reading is service practice. It is not a federal requirement, and no one will ever ask you to produce one.
What Part 82 does require on an R-410A system is straightforward, and a residential split system is a high-pressure appliance, so this is Type II work:
| Requirement | Where it comes from |
|---|---|
| Do not knowingly vent or release the refrigerant | Section 608 — 40 CFR 82.154(a) |
| Recover the charge to the required level before opening the appliance | Section 608 — 40 CFR 82.156 |
| Use recovery equipment certified under the standards | Section 608 — 40 CFR 82.158 |
| Target pressures, superheat and subcooling values | Manufacturer — the unit's installation instructions |
| Pulling to 500 microns before charging | Best practice — not a Section 608 evacuation level |
| Nitrogen pressure testing, flowing nitrogen while brazing | Best practice — not Part 82 |
Two details from that table are worth nailing down, because competitors get both wrong.
The evacuation level. Under Table 1 of 82.156, a high-pressure appliance with a full charge of less than 200 pounds requires a vacuum of 0 inches of mercury — atmospheric pressure — before you open it. Almost every residential R-410A system falls in that row. The deep vacuum you pull afterwards to dehydrate the system before charging is good practice and the right thing to do, but it is not what the recovery rule is asking for.
The 1993 date. Where Table 1 splits on November 15, 1993, that date refers to the manufacture or import date of the recovery equipment, not the age of the appliance you are working on. This is the most commonly inverted fact in the whole program, and it turns up on the exam regularly.
What this means on the job
Stop reading the gauges as a verdict. Read them as one of four inputs.
Concretely: set the manifold to R-410A before you connect it, take both pressures and both line temperatures, calculate superheat and subcooling, and compare against the number on the data plate or in the installation instructions. If the calculated values are in range, the pressures are correct by definition, whatever they look like.
If the system has lost charge, remember that R-410A is still a blend. Recover, repair the leak, evacuate, and weigh in a full charge rather than topping off. And if you are about to start working on A2L equipment, get used to reading two columns now — the transition removes the shortcut R-410A gave you for a decade. If you are still working toward Type II, the practice questions on recovery, evacuation and blends cover exactly the material these systems lean on hardest.
Frequently asked questions
How do you use a PT chart for R-410A?
Read the pressure on your gauge, find the matching psig value in the R-410A column, and read across to the temperature. That temperature is the saturation temperature of the refrigerant at that pressure. Compare it to the measured line temperature to get superheat on the suction side or subcooling on the liquid side.
What is a good low-side pressure for R-410A?
There is no fixed correct value, because suction pressure tracks the evaporator coil temperature, which moves with indoor load, airflow and humidity. A reading around 118 psig corresponds to a 40 °F coil, which is typical under moderate conditions, but the only way to judge the charge is to calculate superheat or subcooling and compare against the manufacturer's target.
Why are R-410A pressures so much higher than R-22?
R-410A is a higher-pressure refrigerant by chemistry — roughly 60 to 65 percent above R-22 at the same saturation temperature. That is why R-410A equipment uses different components, different gauges and higher-rated tubing, and why R-410A was never a drop-in for an R-22 system.
Does R-410A have temperature glide?
Barely. R-410A is near-azeotropic, with glide commonly cited at under about 0.3 °F, which is small enough to ignore in service. That is why its PT chart prints a single saturation column. True zeotropic blends such as R-407C and R-454B print separate dew and bubble values because their glide is large enough to change the math.
Can I use an R-410A chart for R-454B?
No. R-454B reads lower than R-410A at every temperature — about 107 psig against 118 psig at 40 °F. Reading an R-454B system against an R-410A chart makes a correct charge look low, which leads directly to overcharging. Set the manifold to the refrigerant actually in the system.
Is taking a PT reading required by EPA Section 608?
No. Pressure-temperature readings, superheat targets and charging procedure are service practice set by the equipment manufacturer. Section 608 governs venting, recovery levels, recovery equipment certification, leak repair and recordkeeping. Certification is also decided by appliance class rather than by refrigerant, and it does not expire.
Sources
Notice
Get EPA 608 is an independent study aid. It is not affiliated with, endorsed by, or approved by the U.S. Environmental Protection Agency, the ESCO Institute, Mainstream Engineering, or HVAC Excellence.