Refrigerant PT chart

What a PT chart actually tells you and why every HVAC tech needs one

A pressure-temperature chart is the most-used reference document in HVAC service work. It plots the saturation pressure of a refrigerant against its saturation temperature. At saturation, the refrigerant exists as a mix of liquid and vapor at equilibrium, and pressure and temperature are locked to each other. Read one, you know the other. That relationship is the entire basis for superheat and subcooling measurements, which diagnose nearly every refrigerant-side problem in an air conditioner or heat pump.

On the suction side of an operating system, you read low-side pressure on your manifold gauges and convert to saturation temperature using the PT chart. Subtract that from the measured suction-line temperature and you have superheat. On the liquid side, read high-side pressure, convert to saturation, and subtract the measured liquid line temperature to get subcooling. Both are the foundational diagnostic numbers for charging, troubleshooting low refrigerant, finding a restriction, or confirming a metering device is working.

R-410A pressure-temperature chart and how to read it

R-410A is the residential refrigerant that has dominated US AC and heat pump equipment from 2010 through the 2024 model year. At 47 degrees Fahrenheit saturation, R-410A sits at 144.7 PSIG. At 80 degrees the saturation pressure is 265.5 PSIG. At 110 degrees (typical liquid-line saturation on a hot day) it climbs to 414.9 PSIG. Those numbers are what your gauges should show on the corresponding lines if the system is correctly charged and operating within design.

R-410A is technically a near-azeotropic blend of R-32 and R-125, with a glide of about 0.3 degrees Fahrenheit which is small enough that industry treats it as zero. You use a single saturation pressure for both superheat and subcooling. That changes with R-454B. R-410A is being phased out for new equipment production under the EPA AIM Act, so service stock will tighten and prices will rise over the next several years. Recharging a leaking R-410A unit installed 10+ years ago is increasingly hard to justify on cost.

Temperature (°F)	Pressure (PSIG)
-20	28.8
-15	34.4
-10	39.9
-5	46.5
0	53
5	60.7
10	68.4
15	77.4
20	86.4
25	96.8
30	107.3
35	119.3
40	131.3
45	144.7
50	159
55	174.1
60	190.2
65	207.4
70	225.7
75	245
80	265.5
85	287.2
90	310.1
95	334.2
100	359.7
105	386.6
110	414.9
115	444.6
120	475.9
125	508.8
130	543.3

R-454B pressure-temperature chart: why glide changes how you read it

R-454B is one of the two A2L refrigerants replacing R-410A in new residential equipment. It is a zeotropic blend of 68.9 percent R-32 and 31.1 percent R-1234yf with a temperature glide of about 1.5 degrees Fahrenheit. Glide means the refrigerant does not boil or condense at a single temperature: it has a bubble point (where the first vapor bubble forms in the liquid) and a dew point (where the last liquid drop evaporates to vapor). At 80 degrees saturation, R-454B sits at 237.3 PSIG on the bubble line and 246.0 PSIG on the dew line.

The rule for using a glide refrigerant is straightforward but easy to get wrong. For superheat measurements on the suction line, use the dew point (vapor saturation) because the refrigerant has fully evaporated to vapor at that point in the cycle. For subcooling measurements on the liquid line, use the bubble point (liquid saturation) because the refrigerant is fully condensed to liquid. Reading the wrong line introduces a 1.5 degree error, which is significant when you are charging to a 10-degree subcool target.

Temperature (°F)	Bubble PSIG	Dew PSIG	Glide
-20	25.4	27.4	2
-15	30.4	32.6	2.2
-10	35.4	37.8	2.4
-5	41.3	43.9	2.6
0	47.2	50	2.8
5	54.1	57.1	3
10	61	64.3	3.3
15	69	72.6	3.6
20	77.1	80.9	3.8
25	86.4	90.5	4.1
30	95.7	100.1	4.4
35	106.3	111.1	4.8
40	117	122.1	5.1
45	128.9	134.3	5.4
50	141.7	147.4	5.7
55	155.3	161.5	6.2
60	169.8	176.4	6.6
65	185.2	192.3	7.1
70	201.6	209.2	7.6
75	218.9	227.1	8.2
80	237.3	246	8.7
85	256.7	266	9.3
90	277.2	287.1	9.9
95	298.9	309.4	10.5
100	321.7	332.8	11.1
105	345.7	357.5	11.8
110	370.9	383.5	12.6
115	397.5	410.8	13.3
120	425.3	439.5	14.2
125	454.6	469.6	15
130	485.3	501.2	15.9

R-454B vs R-410A pressures: side-by-side comparison

R-454B operates at very similar pressures to R-410A, which is intentional. Equipment manufacturers designed R-454B systems to drop into the same compressor and component families with minimal redesign. Pressures run about 5 percent lower at the same saturation temperature, but the gauge needle position looks familiar to any technician coming from R-410A:

• At 40°F: R-410A reads 131.3 PSIG, R-454B reads 117.0 bubble / 122.1 dew
• At 80°F: R-410A reads 265.5 PSIG, R-454B reads 237.3 bubble / 246.0 dew
• At 110°F: R-410A reads 414.9 PSIG, R-454B reads 370.9 bubble / 383.5 dew

R-32 (the other A2L replacement, used by Daikin, Mitsubishi, LG, and others) reads different values entirely and runs higher pressure than R-410A. Always confirm which refrigerant is in the system before charging. The nameplate on the outdoor unit lists the refrigerant; do not assume from the year or the brand.

R-22 PT chart for legacy equipment service

R-22 has been banned for production and import in the US since 2020, but plenty of pre-2010 equipment is still in service and will need topping off or full recharge from recycled stock. R-22 reads dramatically lower pressures than R-410A at the same saturation temperature: 68.6 PSIG at 40°F (vs 131.3 for R-410A), 143.6 PSIG at 80°F (vs 265.5), 226.4 PSIG at 110°F (vs 414.9). Reading a R-22 chart while charging an R-410A system, or vice versa, can damage equipment and is a common rookie mistake.

R-22 service stock is sold at four to ten times its pre-ban price and gets more expensive every year. Most contractors will not warranty work on a leaking R-22 system. If your system uses R-22 and needs more than a pound of refrigerant added, run our replace vs repair calculator before paying for the recharge. The math almost always favors replacement.

How temperature glide affects refrigerant charging

Charging a glide refrigerant like R-454B is slightly more involved than a single-line refrigerant. Liquid charging through the liquid line is preferred because the refrigerant enters the system as a liquid at known composition. Vapor charging from the can changes the composition of the remaining refrigerant in the cylinder as it boils off (the lower boiling component leaves first), which throws off the composition of what ends up in the system. For R-454B, that means using a charging scale and adding liquid by weight whenever possible.

Subcooling measurements are also slightly more meaningful than superheat measurements on R-454B systems because the bubble point you measure against has less error than the dew point in real-world conditions. Most manufacturers (Carrier, Trane, Lennox, Bryant) publish R-454B charging tables that use subcool only, which is a hint that the industry is leaning into that practice.

Common PT chart mistakes that destroy a service call

Five mistakes show up repeatedly in field training and warranty claims:

• Using the wrong refrigerant chart. Always confirm the refrigerant from the nameplate, not the equipment age or the technician's memory.
• Forgetting PSIG vs PSIA. Manifold gauges read PSIG (gauge, atmospheric pressure subtracted). PT charts in this tool show PSIG. Some textbook charts list PSIA which is 14.7 PSI higher. Mixing them is a common source of off-by-15 errors.
• Ignoring glide on R-454B and R-407C. Reading bubble where you should read dew (or vice versa) introduces 1.5°F to 3°F of saturation temperature error, which destroys superheat and subcool diagnoses.
• Measuring near the metering device or compressor. Superheat must be measured at least 6 inches downstream of the evaporator outlet on a section without thermal interference. Liquid temperature must be measured downstream of the condenser, not in the discharge line.
• Not accounting for ambient temperature on gauge accuracy. Manifold gauges drift with temperature. Calibrate against a known reference at least annually, and check the zero reading at atmospheric pressure before every service.

Using the PT chart with superheat and subcooling for full charge verification

The PT chart is the input to a complete refrigerant charge verification, not the output. The full procedure is: measure suction pressure with the manifold, convert to saturation temperature using the PT chart (dew side for glide refrigerants), measure suction line temperature with a clamp-on thermocouple, subtract to get superheat, compare to target from the manufacturer's charging table or our superheat calculator. Then repeat the process on the liquid line for subcooling, comparing against our subcooling calculator. Both numbers in specification means the charge is correct. Either out of spec points to a specific failure mode (low charge, restriction, dirty condenser, oversized metering device).