Automotive Air Conditioning Pressure Chart: A Complete Guide 

Car air conditioning has changed and gotten better over time. It began with basic systems and open windows. Now, we have advanced setups in our cars. One crucial thing to keep an eye on is the refrigerant pressure. Especially with the commonly used R134a. Let’s understand how car AC systems work. We’ll also look at the automotive air conditioning pressure chart. Additionally, we’ll provide troubleshooting tips related to pressure issues in AC systems.

How Does Automotive Air Conditioning Work? 

To understand how a car’s air conditioning works, let’s look at the basics. The system’s main job is to take away heat from inside the car. It does this using special fluids called refrigerants. These fluids go between being a high-pressure liquid and a low-pressure gas. This back-and-forth helps them take away heat and humidity from the car, giving us cool and dry air.

Different parts like the compressor, condenser, accumulator, and evaporator all work together. These make the inside of the car comfortable. The refrigerant, which is cold and under low pressure, takes in heat when it turns from a liquid to a gas. Then, it releases that heat when it changes back from a gas to a liquid, but now it’s hot and under high pressure.

Refrigerant Properties:

A critical player in the cooling process, the refrigerant must possess specific properties:

  • Non-explosive and non-flammable
  • Low boiling point
  • Non-corrosive to metals mixes well with oils
  • Non-hazardous, safe, and non-toxic
  • Large latent heat value
  • Easy to liquify or vaporize, moderate pressure and temperature

Popular and industry-approved refrigerants:

  • R-12
  • R-134a
  • Freon
  • Freeze-12
  • GHG-HP
  • Hot Shot
  • Ikon-12
  • R-406A
  • Among others

R134a Refrigerant:

Because of environmental worries, R-12 was phased out. And, R134a has become the new standard in the industry. R134a has similar thermodynamic properties but is less harmful to the ozone layer. It has been widely accepted as a replacement. At atmospheric pressure, its boiling point is -26.8°C, and it rises to -10.6°C at 10 psi pressure.

Low Side and High Side Pressure 

In a car’s AC system, the refrigerant goes back and forth between liquid and gas in a closed loop. This change in pressure is connected to temperature shifts. It makes a high-pressure side and a low-pressure side.

The compressor takes low-pressure gas from the evaporator and squeezes it into high-pressure gas. This high-pressure gas goes to the condenser turning into high-pressure liquid and releasing heat. The filtered high-pressure liquid goes through a thermal expansion valve, becoming a low-pressure liquid. It then reaches the evaporator, boiling and becoming low-pressure gas again. Keeping an eye on both low and high side pressures is important to understand how the refrigerant is doing in the system.

Automotive Air Conditioning Pressure Chart

To check the pressure of the refrigerant in a car’s AC system, you use a special testing device. This device has two pressure gauges connected to a manifold assembly. The AC Pressure Chart for R134a is a useful guide. It gives you typical pressure values for both the high and low sides at different temperatures. This chart is handy for technicians and people who like doing it themselves. Plus it helps figure out potential problems in the AC system.

Automotive Air Conditioning Temperature Chart For R134a Refrigerant


  • in °F
  • in °C

Low Side Pressure:

  • in psi
  • in kPa

High Side Pressure:

  • in psi
  • in kPa
Temperature Low Side Pressure High Side Pressure
18°F / -8°C 25-35 psi / 172-241 kPa 135-155 psi / 931-1069 kPa
21°F / -6°C 35-40 psi / 241-276 kPa 145-160 psi / 1000-1103 kPa
24°F / -4°C 35-40 psi / 241-276 kPa 150-170 psi / 1034-1172 kPa
27°F / -3°C 40-50 psi / 276-345 kPa 175-210 psi / 1207-1448 kPa
29°F / -2°C 45-55 psi / 310-379 kPa 225-250 psi / 1551-1724 kPa
32°F / 0°C 45-55 psi / 310-379 kPa 250-270 psi / 1724-1862 kPa
35°F / 2°C 50-55 psi / 345-379 kPa 275-300 psi / 1896-2068 kPa
38°F / 3°C 50-55 psi / 345-379 kPa 315-325 psi / 2172-2241 kPa
41°F / 5°C 50-55 psi / 345-379 kPa 330-335 psi / 2275-2310 kPa
43°F / 6°C 50-55 psi / 345-379 kPa 340-345 psi / 2344-2379 kPa

How To Use The Automotive Air Conditioning Pressure Chart

If your car’s AC isn’t working well, an important thing to do is check the refrigerant pressure. An AC technician will use the AC Pressure Chart to make sure that both the high and low side pressure readings are in the right range. The chart helps figure out potential problems by looking at pressure changes. It’s essential to remember that releasing R134a into the air is against the law in many countries. It includes the U.S. also.

Auto Air Conditioning Temperature Chart Use: Troubleshooting Guide

Low Side Pressure:

  • Within range
  • Low

High Side Pressure:

  • Within range
  • Low
  • High
Low Side Pressure High Side Pressure Diagnosis
Within range Within range No problem. AC is working fine.
Low Low Refrigerant is Low. Add some refrigerant.
Low High Possible Blockage in Expansion Valve or Orifice Tube. Service Needed.
High High Problem with Compressor. Service or Replacement.
Low High Refrigerant Overload. Vent extra R134a with proper care.

Note: Use the troubleshooting guide and automotive AC temperature chart to identify issues with your car’s AC system. Look at the combination of low and high side pressures to identify potential issues. Always be careful and follow safety guidelines when working with refrigerants.


Know your automotive air conditioning system. Use the R134a Pressure Chart and Troubleshooting Guide. By understanding the system and chart, you can effectively find and fix issues. This helps ensure a comfortable and efficient driving experience. Keep an eye on things regularly. Follow the recommended pressure levels. this awareness will help the AC system last longer and work at its best.


1. Why monitor low-side and high-side pressures in a car’s AC system?

Answer: It’s crucial for diagnosing issues, and ensuring optimal performance. Plus it prevents expensive repairs.

2. Why is R134a the industry standard in automotive AC systems?

Answer: R134a is chosen for its similar properties to the phased-out R-12. Additionally, a reduced impact on the ozone layer. Note that its use is gradually being replaced by HFO-1234yf.

3. How does the AC Pressure Chart help in troubleshooting car AC issues?

Answer: The chart provides reference values for pressure at different temperatures. It helps technicians identify problems. Additionally, this maintains optimal refrigerant levels for efficient air conditioning.

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