R-134a Ambient Temperature and System Pressure Relationship Chart

R134a Pressure Gauge Chart

 This chart details how ambient temperature correlates with the system refrigerant charge pressure, and how it affects high and low side psi readings. It can be used for recharging refrigerant, or to diagnose an a/c system based on pressure readings from your gauges.

Ambient Temperature (°F)Low SideHigh Side
110°50-55 psi335-345 psi
105°50-55 psi325-335 psi
100°50-55 psi300-325 psi
95°50-55 psi275-300 psi
90°50-55 psi250-275 psi
85°50-55 psi220-250 psi
80°45-50 psi175-220 psi
75°40-45 psi150-175 psi
70°35-40 psi140-165 psi
65°25-35 psi135-155 psi


 A/C System Pressure Troubleshooting

 In conjunction with a set of high and low side gauges, this temperature and pressure relationship charge can be used to diagnose an a/c compressor that is not working.

Low Side and High Side Pressures are Low
• Refrigerant charge below manufacturer specification
• A/C compressor not engaged / variable displacement inoperable
• A/C compressor performance deteriorating

Low Side and High Side Pressures are High
• Refrigerant charge above manufacturer specification
• Condenser fan inoperable
• Condenser dirty / airflow obstruction
• Internal obstruction of condenser

Low Side Pressure Low, High Side Pressure High
• System restriction

Pressures at or Near Equal
• A/C compressor failing internally
• A/C compressor variable displacement function inoperable
• Expansion valve failure