R-134a vs R-1234yf
Key Differences
R-1234yf was chosen for automotive AC because its pressure curve nearly overlaps R-134a's, so compressors and condensers needed only small changes. Service fittings differ on purpose, and R-1234yf is A2L, so it requires SAE J2843 recovery equipment. The two must never be mixed.
Pressure at common saturation temperatures:
- 0°F: R-134a 6.5 PSIG vs R-1234yf 9.2 PSIG (+2.7 PSI, +13% absolute)
- 40°F: R-134a 35.0 PSIG vs R-1234yf 38.4 PSIG (+3.4 PSI, +7% absolute)
- 70°F: R-134a 71.1 PSIG vs R-1234yf 73.9 PSIG (+2.8 PSI, +3% absolute)
- 100°F: R-134a 124.2 PSIG vs R-1234yf 124.9 PSIG (+0.7 PSI, +1% absolute)
- 120°F: R-134a 171.2 PSIG vs R-1234yf 169.2 PSIG (−2.0 PSI, −1% absolute)
Pressure Comparison Graph
Side-by-Side Pressures (PSIG)
| Temp | R-134a | R-1234yf | Δ PSIG |
|---|---|---|---|
| -55°F | -10.0 | -8.8 | +1.2 |
| -50°F | -9.2 | -7.8 | +1.4 |
| -45°F | -8.3 | -6.8 | +1.5 |
| -40°F | -7.3 | -5.7 | +1.6 |
| -35°F | -6.1 | -4.4 | +1.7 |
| -30°F | -4.8 | -2.9 | +1.9 |
| -25°F | -3.4 | -1.4 | +2.0 |
| -20°F | -1.8 | 0.4 | +2.2 |
| -15°F | -0.0 | 2.3 | +2.3 |
| -10°F | 1.9 | 4.4 | +2.5 |
| -5°F | 4.1 | 6.7 | +2.6 |
| 0°F | 6.5 | 9.2 | +2.7 |
| 5°F | 9.1 | 12.0 | +2.9 |
| 10°F | 11.9 | 14.9 | +3.0 |
| 15°F | 15.0 | 18.1 | +3.1 |
| 20°F | 18.4 | 21.6 | +3.2 |
| 25°F | 22.1 | 25.4 | +3.3 |
| 30°F | 26.1 | 29.4 | +3.3 |
| 35°F | 30.4 | 33.8 | +3.4 |
| 40°F | 35.0 | 38.4 | +3.4 |
| 45°F | 40.1 | 43.4 | +3.3 |
| 50°F | 45.4 | 48.8 | +3.4 |
| 55°F | 51.2 | 54.5 | +3.3 |
| 60°F | 57.4 | 60.6 | +3.2 |
| 65°F | 64.0 | 67.0 | +3.0 |
| 70°F | 71.1 | 73.9 | +2.8 |
| 75°F | 78.7 | 81.3 | +2.6 |
| 80°F | 86.7 | 89.0 | +2.3 |
| 85°F | 95.2 | 97.2 | +2.0 |
| 90°F | 104.3 | 105.9 | +1.6 |
| 95°F | 113.9 | 115.1 | +1.2 |
| 100°F | 124.2 | 124.9 | +0.7 |
| 105°F | 135.0 | 135.1 | +0.1 |
| 110°F | 146.4 | 145.9 | -0.5 |
| 115°F | 158.4 | 157.3 | -1.1 |
| 120°F | 171.2 | 169.2 | -2.0 |
| 125°F | 184.6 | 181.8 | -2.8 |
| 130°F | 198.7 | 195.0 | -3.7 |
| 135°F | 213.6 | 208.9 | -4.7 |
| 140°F | 229.2 | 223.4 | -5.8 |
| 145°F | 245.7 | 238.7 | -7.0 |
| 150°F | 262.9 | 254.7 | -8.2 |
| 155°F | 281.0 | 271.4 | -9.6 |
| 160°F | 300.0 | 288.9 | -11.1 |
| 165°F | 320.0 | 307.3 | -12.7 |
| 170°F | 340.8 | 326.5 | -14.3 |
| 175°F | 362.7 | 346.6 | -16.1 |
| 180°F | 385.6 | 367.6 | -18.0 |
| 185°F | 409.7 | 389.7 | -20.0 |
| 190°F | 434.8 | 412.8 | -22.0 |
| 195°F | 461.2 | 437.0 | -24.2 |
Frequently Asked Questions
Can R-134a and R-1234yf be used interchangeably?
No. R-1234yf and R-134a systems use different service port sizes to prevent cross-contamination, and require different PAG oils. Cross-contaminating them can damage the compressor and is illegal under EPA regulations.
Do R-134a and R-1234yf have the same pressure?
Almost identical. At 70°F: R-134a = 71.1 PSIG, R-1234yf = 73.9 PSIG — a difference of only 2.8 PSIG. Across the full temperature range, pressures stay within about 5% of each other, which is why the transition required minimal system redesign.