R-134a pressure-temperature chart
R-134a saturation pressures from -40 °F to 150 °F, in gauge pressure (psig), with vacuum shown in inches of mercury. At 40 °F, R-134a saturates at 35.0 psig; at 105 °F, 135.0 psig.
R-134a PT chart (psig, every 5 °F)
| °F | °C | Pressure psig |
|---|---|---|
| -40 | -40.0 | 14.8 inHg vac |
| -35 | -37.2 | 12.5 inHg vac |
| -30 | -34.4 | 9.8 inHg vac |
| -25 | -31.7 | 6.9 inHg vac |
| -20 | -28.9 | 3.7 inHg vac |
| -15 | -26.1 | 0.1 inHg vac |
| -10 | -23.3 | 1.9 |
| -5 | -20.6 | 4.1 |
| 0 | -17.8 | 6.5 |
| 5 | -15.0 | 9.1 |
| 10 | -12.2 | 11.9 |
| 15 | -9.4 | 15.0 |
| 20 | -6.7 | 18.4 |
| 25 | -3.9 | 22.1 |
| 30 | -1.1 | 26.1 |
| 35 | 1.7 | 30.4 |
| 40 | 4.4 | 35.0 |
| 45 | 7.2 | 40.1 |
| 50 | 10.0 | 45.4 |
| 55 | 12.8 | 51.2 |
| 60 | 15.6 | 57.4 |
| 65 | 18.3 | 64.0 |
| 70 | 21.1 | 71.1 |
| 75 | 23.9 | 78.7 |
| 80 | 26.7 | 86.7 |
| 85 | 29.4 | 95.2 |
| 90 | 32.2 | 104.3 |
| 95 | 35.0 | 114.0 |
| 100 | 37.8 | 124.2 |
| 105 | 40.6 | 135.0 |
| 110 | 43.3 | 146.4 |
| 115 | 46.1 | 158.4 |
| 120 | 48.9 | 171.2 |
| 125 | 51.7 | 184.6 |
| 130 | 54.4 | 198.7 |
| 135 | 57.2 | 213.6 |
| 140 | 60.0 | 229.2 |
| 145 | 62.8 | 245.7 |
| 150 | 65.6 | 262.9 |
Need a reading between rows, or your elevation corrected? Use the tool above: type a temperature or a pressure and it fills in the other.
About R-134a
R-134a is a single-component HFC used in medium-temperature refrigeration, chillers, and car air conditioning in older vehicles. Car AC is covered by EPA Section 609 certification; stationary equipment by Section 608.
It runs at much lower pressure than AC refrigerants: below about -15 °F its saturation pressure is under atmospheric, shown here as inches of mercury of vacuum.
How to read a PT chart
A pressure-temperature chart gives the saturation temperature: the temperature at which the refrigerant boils or condenses at a given pressure. Inside the evaporator and condenser, where liquid and vapor are both present, pressure and temperature are locked together, so one gauge reading tells you the other.
- Find your pressure on the chart (or type it into the tool) and read the saturation temperature next to it.
- Superheat = suction line temperature − saturation temperature at suction pressure. Use the superheat calculator.
- Subcooling = saturation temperature at liquid line pressure − liquid line temperature. Use the subcooling calculator.
- Gauges read psig, pressure above the air around you. Charts are built for sea level (14.696 psi). At 5,000 ft your gauge reads about 2.5 psi high against the chart; enter your elevation in the tool and it corrects for it.
Working on refrigerant circuits?
Opening the refrigerant circuit on stationary equipment using the refrigerants on this page requires EPA Section 608 certification, and suppliers can only sell you most refrigerants if you have it. See how to get EPA 608 certified or take the free EPA 608 practice tests.
Where the numbers come from
Saturation pressures for R-134a: NIST Chemistry WebBook (NIST Standard Reference Database 69). Converted to gauge pressure at sea level (psig = psia − 14.696); below 0 psig the chart shows inches of mercury of vacuum. Values are for pure refrigerant: air, moisture or a mixed charge will throw readings off. The equipment manufacturer's charging chart and data plate govern.
FAQ
What is R-134a pressure at 40 degrees?
35.0 psig at sea level.
Does this chart work for car AC?
Yes, the saturation pressures are the same refrigerant. But a car's low-side reading changes with engine speed, blower and ambient temperature, so use the vehicle maker's charge procedure, which is usually by weight.
Is this tool free?
Yes. No account, no email, no download. It runs in your browser and works on your phone at the unit.