Refrigerant PT Charts: R-410A, R-32 and R-22 Pressure-Temperature Tables

What a PT chart tells you

Inside an evaporator or condenser, refrigerant is boiling or condensing. While liquid and vapor coexist, pressure and temperature are locked together: at a given pressure the refrigerant can only be at one temperature, its saturation temperature. A pressure-temperature (PT) chart lists those matching pairs.

That lets a technician use a pressure gauge as a thermometer for the inside of the coil. Suction pressure converts to the evaporator's boiling temperature; head pressure converts to the condenser's condensing temperature. Comparing those with actual pipe temperatures gives superheat and subcooling, which is how charge is verified (see how AC refrigerant charge is checked).

The chart only applies where the refrigerant is saturated. Vapor leaving the evaporator is superheated and liquid leaving the condenser is subcooled, so their temperatures are expected to differ from the chart value. That difference is the measurement.

Using the PT lookup

Pick a refrigerant and enter a temperature to read its saturation pressure, or enter a gauge reading to find the saturation temperature that matches it. The lookup interpolates linearly between the 5 °F rows of the chart below, so a value between rows is accurate to within a fraction of a psi.

The reverse lookup is the one you use in the field: the saturation temperature at suction pressure is what you subtract from the suction-line temperature to get superheat, and the saturation temperature at liquid pressure is what you compare with the liquid-line temperature for subcooling.

Example: R-410A at a suction pressure of 118 psig saturates at 40 °F. A suction-line reading of 52 °F means 12 °F of superheat.

Saturation pressure chart, 20 to 120 °F

Gauge pressure (psig) at sea level. R-410A and R-32 are rounded to the nearest psig; R-22 is shown to one decimal.

For charging, use the PT data published by the equipment or refrigerant manufacturer, or the built-in tables in a digital manifold. Small differences between sources (a psi or two) are normal and come from rounding and the property data each one uses.

How to read the chart, step by step

1. Identify the refrigerant from the outdoor unit's nameplate. Using the wrong column is the most common PT mistake.
2. Read the gauge once the system has run 10 to 15 minutes and pressures are steady.
3. Find the pressure in that refrigerant's column and read across to the temperature. Interpolate between rows: R-410A at 124 psig is about halfway between 40 °F (118) and 45 °F (130), so roughly 42.5 °F.
4. Compare with the pipe temperature. Suction line temperature minus suction saturation temperature is superheat. Condensing saturation temperature minus liquid line temperature is subcooling. Our superheat and subcooling calculator does the subtraction.

Worked example: an R-410A system shows 118 psig suction and 340 psig liquid line. The chart gives about 40 °F evaporator saturation and about 105 °F condensing saturation. If the suction line reads 50 °F and the liquid line 95 °F, superheat is 10 °F and subcooling is 10 °F.

Typical operating pressures and what they mean

Pressures move with load, so there is no single correct number. As a rough guide for a cooling system running in normal conditions:

• Evaporator saturation is usually around 38 to 45 °F, which is about 113 to 130 psig on R-410A or 65 to 76 psig on R-22. Much lower suggests low airflow, low charge or a restriction; much higher can mean overcharge or a high indoor load.
• Condensing saturation typically runs about 15 to 30 °F above outdoor air temperature. High-efficiency units with large condenser coils sit at the low end. On a 95 °F day that puts R-410A head pressure roughly in the 340 to 420 psig range.

A dirty condenser coil, failed condenser fan or overcharge pushes head pressure up. See outside AC unit not running if the fan has stopped.

Why R-454B needs two columns

R-22 and R-32 are effectively single substances, and R-410A is a near-azeotropic blend whose two components boil at almost the same temperature, so one column works. R-454B, one of the low-GWP replacements covered in our refrigerant types guide, is a zeotropic blend of R-32 and R-1234yf. At a fixed pressure it starts boiling at one temperature (the bubble point) and finishes at a slightly higher one (the dew point). That spread, the temperature glide, is roughly 1 to 2 °F for R-454B.

PT charts for R-454B therefore list a dew-point (vapor) and a bubble-point (liquid) temperature. The rule is: use the dew point for superheat on the suction side and the bubble point for subcooling on the liquid side. Its pressures run slightly below R-410A at the same temperature. We have not included an R-454B column here because charging should be done from the manufacturer's dew and bubble tables, which digital gauges also carry.

Altitude and gauge type

The table is in psig, pressure above the surrounding atmosphere. At high elevations atmospheric pressure is lower, so a mechanical gauge reads slightly high relative to absolute pressure: about 2.5 psi at 5,000 ft. On the low side of R-22 that is worth around 1 to 2 °F, which matters for a precise superheat reading. Digital manifolds that measure absolute pressure (psia) or let you enter elevation remove this error.

Frequently asked questions