Engine at idle, blower on HIGH, A/C on MAX with recirculation, system stabilized. Reference ranges only: charge by weight to the OEM spec.
| Outside temp | Low side | High side |
|---|---|---|
| 65°F | 25–35 psi | 135–155 psi |
| 75°F | 35–45 psi | 150–170 psi |
| 85°F | 45–55 psi | 225–250 psi |
| 95°F | 50–55 psi | 275–300 psi |
| 105°F | 50–55 psi | 315–340 psi |
Healthy R-134a readings at idle (~800–1,000 rpm), blower on HIGH, A/C on MAX/RECIRC, at thermal stability. Field rule: a healthy high side runs about 2.2–2.5× the ambient temperature in °F (≈176–200 psi on an 80 °F day). High side climbs sharply with poor condenser airflow and higher rpm. The 105 °F row is a conservative extrapolation; defer to your OEM spec.
| Outside temp | Low side | High side |
|---|---|---|
| 65°F | 28–38 psi | 135–154 psi |
| 75°F | 38–48 psi | 149–168 psi |
| 85°F | 49–58 psi | 220–243 psi |
| 95°F | 53–58 psi | 266–289 psi |
| 105°F | 53–60 psi | 305–330 psi |
R-1234yf (in most US vehicles built ~2017 onward) is close to R-134a but the high side usually reads a touch LOWER at the same ambient, while the low side sits a few psi HIGHER. yf systems are charge-sensitive: never diagnose one off an R-134a chart, never cross-charge the two, and always charge by weight to the OEM spec.
Reference ranges compiled from published refrigerant charts. The under-hood label and the OEM service spec always win. A/C gauge readings guide ↗