Technical Reference

R134a PT Chart

️ Pressure-Temperature 📊 Field Reference
Understanding the PT Chart
This pressure-temperature chart shows the relationship between pressure and temperature for R134a refrigerant. Use this chart to determine saturation temperatures for superheat and subcooling calculations.
R134a Pressure-Temperature Chart
Temp °F Pressure PSI Temp °F Pressure PSI
0 6.7 70 72.1
5 9.3 75 79.8
10 12.2 80 88.1
15 15.3 85 96.8
20 18.7 90 106.1
25 22.4 95 116.0
30 26.4 100 126.4
35 30.8 105 137.5
40 35.5 110 149.2
45 40.6 115 161.5
50 46.0 120 174.5
55 51.9 125 188.3
60 58.2 130 202.7
65 64.9
How to Use This Chart
Follow these steps to use the PT chart for superheat and subcooling calculations.
1
For Superheat Calculations
  1. Measure low-side pressure with your gauge
  2. Find the pressure in the chart
  3. Read the corresponding saturation temperature
  4. Subtract from actual suction line temperature

Example: 35 PSI ≈ 39°F saturation temperature

2
For Subcooling Calculations
  1. Measure high-side pressure with your gauge
  2. Find the pressure in the chart
  3. Read the corresponding saturation temperature
  4. Subtract actual liquid line temperature

Example: 175 PSI ≈ 121°F saturation temperature

Common Operating Ranges
Typical pressure ranges you'll see in Bobcat AC systems under different conditions.
Condition Ambient Temp Low Side PSI High Side PSI Saturation Temps
Normal Operation 80-95°F 30-45 PSI 175-250 PSI 34-49°F / 121-131°F
High Load 95-105°F 35-50 PSI 200-300 PSI 39-53°F / 129°F+
Low Load 65-75°F 25-35 PSI 150-200 PSI 28-39°F / 111-129°F
Quick Reference Values
Memorize these common pressure-temperature relationships for field work.
Low Side Values
30 PSI ≈ 34°F
35 PSI ≈ 39°F
40 PSI ≈ 44°F
45 PSI ≈ 49°F
50 PSI ≈ 53°F
High Side Values
135 PSI ≈ 104°F
150 PSI ≈ 110°F
165 PSI ≈ 116°F
180 PSI ≈ 122°F
200 PSI ≈ 129°F
Field Tips
Practical tips for using PT charts in real-world conditions.
← Back to Superheat & Subcooling Back to Refrigerant Cycle →