Normal AC Pressures by Outdoor Temperature for R-454B and R-410A

On a 95°F day, Lennox's 3-ton EL16KC1-036 on R-454B should run about 336 psig on the liquid line and 133 psig on the suction line, per its published table. A 3-ton R-410A Goodman GSX16 at the same outdoor temperature reads 357 to 381 psig high and 131 to 145 psig low with 75°F/63°F to 80°F/67°F return air at 1,200 CFM.

There is no universal number. Each manufacturer publishes its own operating table, and the high side moves with outdoor temperature far more than the low side, which also answers to the indoor air. This guide puts two real tables side by side, converts them to saturation temperatures, and walks through a field reading. To convert your own readings, use the free refrigerant PT chart, which reads R-454B on both the dew and bubble lines.

What should AC pressures be on a 95°F day?

For the units below, about 336/133 psig on R-454B and 357-381/131-145 psig on R-410A. Lennox gives the EL16KC1-036 a band of plus or minus 10 psig on the liquid line and 5 psig on suction. Goodman's GSX16 table changes with indoor dry bulb and wet bulb, so the R-410A range here covers 75°F/63°F and 80°F/67°F return air at 1,200 CFM.

Here are both tables from 65°F to 115°F outdoor. The Lennox numbers come from Table 1 of the EL16KC1 Unit Information (Lennox service literature Corp. 100121, January 2025), TXV system, 3-ton column. The Goodman numbers come from the expanded cooling data in the GSX16 spec sheet for the 3-ton GSX16 with a CA*F4860 coil and TXV at 1,200 CFM.

All values are psig. Goodman notes that its high and low pressures are measured at the liquid and suction service valves. Lennox does not print the indoor condition for its residential table. It warns that the numbers are typical.

Lennox EL16KC1 Unit Information (Corp. 100121) § Table 1, footnote 1

"Typical pressures; indoor evaporator match-up, indoor air quantity and evaporator load will cause the pressures to vary." - Lennox, lennox.com

Use the table for the equipment on the job. Lennox says the condenser "must be matched with an indoor coil as specified with AHRI," and its pressures assume that match. A different model or coil match has its own numbers. Within one refrigerant, Lennox's own 95°F row runs 326 to 341 psig liquid and 126 to 138 psig suction across its sizes. At 75°F/63°F return air, most of the 21 psig gap between the brands is the refrigerant, about 17 psig at the same condensing temperature on the Daikin chart. Goodman's 357 psig converts to 108.1°F on the R-410A chart, against 107.9°F for Lennox's 336 psig on R-454B. At 80°F/67°F the Goodman unit condenses about 5°F higher, at 381 psig and 112.8°F, so the refrigerant accounts for about 18 of the 45 psig.

Why does the high side move with outdoor temperature more than the low side?

The condenser rejects heat to outdoor air, so its saturation temperature rides a step above ambient, 12.5°F to 13.2°F at every row of the Lennox -036 column. Suction moves far less, 22 psig across 65°F to 115°F against 219 psig on the liquid line. That is still about 9°F of saturation and four times Lennox's 5 psig tolerance, so read suction from the row too.

Convert each pressure to a saturation temperature and the pattern shows. We used the R-454B PT chart printed in the same Lennox manual (saturated liquid for the liquid line, saturated vapor for suction) and the Daikin A1 vs. A2L PT chart for R-410A. Pressures that fall between the chart rows are interpolated, and the over-ambient columns are our arithmetic.

The step over ambient belongs to the condenser coil and the match, and each brand's table sets its own. On the Goodman table it shrinks from 21.7°F to 14.3°F as the weather heats up, and with 75/63 indoor air it runs 17.5°F down to 9.3°F.

The low side also answers to the indoor coil. At 95°F outdoor, 80°F indoor dry bulb and 1,200 CFM, Goodman's suction goes 125, 133, 145 and 154 psig as entering wet bulb rises from 59°F to 63°F, 67°F and 71°F. That is a 29 psig swing from indoor humidity alone, almost the 31 psig the 67°F column moves between 65°F and 115°F outdoor. Both effects are bigger than the tolerance, so match the row to both the outdoor temperature and the return air.

How do you check a reading against the table?

Read the outdoor temperature at the air entering the condenser coil, find the row in the manufacturer's table, and compare both gauges with the stated tolerance. Then convert the liquid pressure to saturated liquid temperature and subtract the liquid line temperature. Pressures screen the system first, and on a TXV system like the EL16KC1 the charge check is that subcooling against the label.

Lennox says to adjust the charge "using the subcooling method." The pressure table tells you whether the system is in the neighborhood. Here is the sequence on the EL16KC1-036 at 95°F outdoor:

1. Clean filter and coils first. The manual reads, "Be sure that filters and indoor and outdoor coils are clean before testing."
2. Check airflow. "Both airflow and refrigerant charge must be monitored," per Lennox, and its Delta-T table gives the target drop across the indoor coil for the entering dry bulb and wet bulb, within plus or minus 3°F.
3. Run the system until pressures and temperatures stabilize, as the manual instructs.
4. Read the liquid line at the liquid service port. The table expects 336 psig, plus or minus 10.
5. Read suction at the suction port. The table expects 133 psig, plus or minus 5.
6. Convert 336 psig to saturated liquid temperature on the Lennox R-454B chart: 107.9°F.
7. Clamp the liquid line near the service port. The approach table for this size says the liquid line runs 4°F over outdoor air, so expect about 99°F.
8. Subcooling is 107.9 minus 99, or 8.9°F. Lennox's subcooling table (Table 3) gives 9°F for this size at 95°F, plus or minus 1°F.

Lennox's three tables agree at this row. Pressure, approach and subcooling all describe the same 336 psig and 99°F liquid line. In the field, a reading can sit inside the pressure band while subcooling sits outside its 1°F band. The subcooling decides. At that resolution, the chart matters too. Our PT chart, built on the CoolProp property library, gives 107.3°F at 336 psig, which makes the same reading 8.3°F of subcooling. The Lennox chart and our CoolProp-based chart differ by 0.6°F at this pressure, so near the edge of the band use the manufacturer's chart.

When the outdoor temperature falls between rows, interpolate. At 90°F the -036 table works out to about 314 psig liquid and 130.5 psig suction, halfway between the 85°F and 95°F rows. That midpoint is our estimate. Lennox prints no 90°F row.

Are 250 and 125 psig normal for R-410A on a 68°F day?

Each gauge alone falls inside the range of the 3-ton Goodman GSX16 match above, but no single return-air column gives both. Interpolating Goodman's 65°F and 75°F rows at 1,200 CFM gives about 234 to 286 psig high and 108 to 137 psig low at 68°F. At 67°F wet bulb, where its suction is about 125 to 129 psig, its high side is about 266 to 275 psig, not 250.

That reading comes from a homeowner on r/hvacadvice who knows the coil leaks and wants the pressures to show how much charge is gone. We don't know the brand, so the Goodman rows are a stand-in, and the 68°F values are our straight-line interpolation.

Each gauge sits inside that band, which runs from 70°F/59°F to 85°F/71°F return air, but the pair doesn't match any one column. At 63°F wet bulb Goodman's high side is about 252 to 260 psig with suction near 115 to 118, and at 67°F the suction is near 125 to 129 with the high side at 266 to 275. The post doesn't give indoor conditions, and Goodman prints no tolerance, so the table can't call the pair normal or abnormal. It can't measure a leak either. Pressures near the table only say the system is in the neighborhood. Lennox's procedure is a weighed-in charge and subcooling against the label, while the Goodman table is expanded performance data with no charging targets in it.

Our second row is another r/hvacadvice post, a system on an 80°F day reading 390/100. The post doesn't name the refrigerant, so we read it as R-410A. Across the same return-air band at 1,200 CFM, it is 59 to 119 psig above Goodman's high side and 14 to 46 psig below its low side, with the evaporator below 32°F. A reading that far off both rows needs a diagnosis before any refrigerant goes in, since the high side is already above the table. Take subcooling and superheat, check the outdoor coil and indoor airflow, and compare total external static pressure with the blower's rated maximum on the static pressure calculator before touching the charge.

Which R-454B column do you read for each gauge?

Saturated liquid (bubble point) for the liquid line and subcooling, saturated vapor (dew point) for suction and superheat. R-454B is a zeotropic blend, so one pressure has two saturation temperatures. On the Lennox chart, 133 psig falls between the 132 and 134 psig rows, at about 49.2°F liquid and 51.5°F vapor, 2.3°F apart. Read the wrong column and every superheat number shifts by that much.

Lennox prints both columns on page 35 of the manual and states which one goes where.

Lennox EL16KC1 Unit Information (Corp. 100121) § R-454B Refrigerant Pressure-Temperature Chart, notes 2 and 3

"Saturated liquid temperature is used to calculate liquid subcooling." - Lennox, lennox.com

The gap is about the same at condensing pressure. At 336 psig the chart gives 107.9°F liquid and 110.2°F vapor. A tech who reads the vapor column for subcooling calls 8.9°F of subcooling 11.2°F and may pull charge from a system that is right.

So read the liquid column when you take subcooling and the vapor column when you take superheat.

What throws off a pressure check?

Five errors throw off a pressure check: an R-410A expectation on an R-454B system, outdoor temperature taken in the sun, readings taken before the system settles, dirty coils or filter, and the wrong refrigerant chart. On the Daikin chart, R-454B runs about 11 psig lower than R-410A on the liquid line at 80°F condensing, 17 psig at 108°F and 20 psig at 120°F. The table below puts a number or a manufacturer's rule on each.

One more check before you blame the charge. Goodman's suction moved 29 psig with indoor wet bulb at a fixed outdoor temperature, so a dry house in the evening and a humid house in the afternoon give different low sides on the same, correct charge.

Checking your own readings with BuildSolver

Pull the operating table from the charging label, unit information or spec sheet for the exact model, or follow the charging label's procedure and target if there is none. Convert each gauge reading on the refrigerant PT chart, which shows dew and bubble lines for R-454B and R-410A and corrects for elevation. Then enter both pressures, both line temperatures and the label subcooling in the superheat and subcooling calculator.

Both pages are free without signup and run in your browser. The PT chart also covers R-32 and R-22, and the calculator reads suction on the dew line and liquid on the bubble line itself. Since the superheat and subcooling calculator works at sea level, correct the gauge reading first at elevation, as its FAQ explains. The PT chart gives saturation only, so it won't tell you whether a pressure is normal for a given outdoor temperature. That comparison needs the manufacturer's table, the way this guide uses Lennox and Goodman.

For where R-454B and R-32 stand for installers, read our A2L refrigerant transition guide.

1. Note outdoor air entering the condenser, return dry bulb and wet bulb, and the model and coil numbers.
2. Find the row in the manufacturer's operating table and note the tolerance.
3. Convert liquid pressure on the bubble line and suction on the dew line with the PT chart.
4. Enter both gauge pressures and both line temperatures in the superheat and subcooling calculator with the label subcooling target.

Sources

• Lennox, EL16KC1 (R-454B) Unit Information, service literature Corp. 100121, January 10, 2025, Table 1 Normal Operating Pressures, Tables 2-3, R-454B PT chart: lennox.com
• Goodman, GSX16 Split System Air Conditioner spec sheet SS-GSX16 (3/21), Expanded Cooling Data, pages 17-18: goodmanmfg.com
• Daikin Comfort Technologies, A1 vs. A2L Pressure Temperature Chart, USA (values by Weitron): chadwellsupply.com
• U.S. EPA, SNAP, Substitutes in Residential and Light Commercial Air Conditioning and Heat Pumps: epa.gov

For estimation purposes only. Charge to the equipment manufacturer's procedure and label.