R134a Pressure Chart
The R134a Pressure Chart is a technical reference tool covering r134a pressure chart, r134a pressure temperature chart, ac refrigerant pressure chart, r134a gauge readings chart. Use the chart below to look up values instantly. Printable and downloadable versions are available on this page.
R134a Pressure-Temperature Chart
| Temperature (°F) | Pressure (psig) — Gauge | Pressure (psia) — Absolute |
|---|---|---|
| -40°F | -15.0 psig | 0 psia (vacuum) |
| -30°F | -10.7 psig | 4.3 psia |
| -20°F | -5.4 psig | 9.6 psia |
| -10°F | 0.3 psig | 15.3 psia |
| 0°F | 6.9 psig | 21.9 psia |
| 10°F | 14.6 psig | 29.6 psia |
| 20°F | 23.4 psig | 38.4 psia |
| 30°F | 33.3 psig | 48.3 psia |
| 40°F | 44.5 psig | 59.5 psia |
| 50°F | 57.0 psig | 72.0 psia |
| 60°F | 70.9 psig | 85.9 psia |
| 70°F | 86.3 psig | 101.3 psia |
| 80°F | 103.3 psig | 118.3 psia |
| 90°F | 121.9 psig | 136.9 psia |
| 100°F | 142.4 psig | 157.4 psia |
| 105°F | 153.3 psig | 168.3 psia |
| 110°F | 164.8 psig | 179.8 psia |
| 115°F | 176.8 psig | 191.8 psia |
| 120°F | 189.4 psig | 204.4 psia |
Source: ASHRAE Refrigerant Handbook — R-134a (1,1,1,2-Tetrafluoroethane) saturated pressure-temperature properties
R134a Normal Operating Pressures for Automotive AC
| Condition | Low Side Pressure (suction) | High Side Pressure (discharge) | What This Indicates |
|---|---|---|---|
| Normal operation (ambient 75°F / 24°C) | 25–45 psig | 150–250 psig | System working correctly |
| Too low on both sides | Below 25 psig | Below 150 psig | Refrigerant leak or low charge. Recharge after leak check. |
| High suction, normal or high discharge | Above 55 psig | 150–250 psig | Possible overcharge, faulty expansion valve, or restricted orifice tube. |
| Both sides high | Above 55 psig | Above 300 psig | Overcharged system, condenser airflow problem, non-condensables (air) in system. |
Normal pressures vary significantly with ambient temperature — hotter ambient air raises both high-side and low-side pressures. Always compare readings to the expected pressure at the current ambient temperature using the chart above. These values are for a typical automotive R134a system at idle with AC set to max cold.
Source: ASE automotive AC diagnostic reference standards
R134a System Specifications Reference
| Property | Value |
|---|---|
| Chemical name | 1,1,1,2-Tetrafluoroethane |
| Chemical formula | CH₂FCF₃ |
| Boiling point at atmospheric pressure | -26.3°F (-32.4°C) |
| Critical temperature | 214.0°F (101.1°C) |
| Critical pressure | 588.7 psia (40.6 bar) |
| Global Warming Potential (GWP) | 1,430 — moderate (being phased out in favour of R1234yf in new vehicles) |
| Ozone Depletion Potential (ODP) | 0 — does not deplete ozone (replaced CFC-12 which had ODP of 1.0) |
| Applications | Automotive AC (1990s–2020s), household refrigerators, commercial refrigeration, heat pumps |
Source: ASHRAE and EPA refrigerant properties database
AC Refrigerant Pressure Reference
Enter the current ambient temperature to get expected R134a high-side and low-side pressures for your system.
| Condition | Low Side | High Side | Likely Cause |
|---|
Frequently Asked Questions
What is R134a used for?
R134a is a hydrofluorocarbon (HFC) refrigerant used primarily in automotive air conditioning systems manufactured from the early 1990s through the mid-2010s. It replaced CFC-12 (Freon) which was phased out for its ozone-depleting properties.
What pressure should R134a be at 90°F ambient?
At 90°F ambient temperature a normally operating automotive R134a system typically shows low-side (suction) pressure of approximately 35–50 psig and high-side (discharge) pressure of approximately 225–275 psig. Higher ambient temperatures produce higher pressures across the system.
How do I know if my R134a system is low on refrigerant?
Low refrigerant charge typically shows both low-side and high-side pressures below normal — the low side may drop below 25 psig and the AC will blow warm or intermittently cool. A leak test should be performed before recharging to find and repair the source of the leak.
What replaced R134a in cars?
R1234yf (HFO-1234yf) has replaced R134a in new vehicle AC systems since approximately 2014 in Europe and 2017 to 2019 in most new US vehicles. R1234yf has a global warming potential (GWP) of only 4 compared to R134a's 1,430.
Can R134a and R1234yf be mixed?
No — mixing refrigerants is unsafe and illegal. R134a and R1234yf have different pressure profiles and use different refrigerant oil formulations — contamination will damage the system and refrigerant recovery equipment.
How do I read R134a gauge pressures?
The low-side (blue) gauge reads suction pressure from the evaporator side — typically 25–45 psig in normal operation. The high-side (red) gauge reads discharge pressure from the compressor outlet — typically 150–250 psig at moderate ambient temperatures.
What is the difference between psig and psia?
PSIG (pounds per square inch gauge) measures pressure relative to atmospheric pressure — a reading of 0 psig equals atmospheric pressure. PSIA (pounds per square inch absolute) measures pressure relative to a perfect vacuum — 0 psia is a complete vacuum and 14.7 psia equals standard atmospheric pressure.
Why are R134a pressures in a vacuum at very low temperatures?
At temperatures below approximately -10°F the saturation pressure of R134a drops below atmospheric pressure — meaning the refrigerant would need to be in a vacuum (below 0 psig) to remain in its normal liquid-vapour equilibrium state. This is why refrigeration systems operating at very low evaporator temperatures must manage vacuum conditions carefully to prevent air infiltration.