Sadly AC is one of those parts of the vehicle that malfunctions often. Most of it is due to negligence in maintaining the AC system and pressure regularly. One such common confusion regarding AC maintenance is choosing the ideal AC pressure while the engine is off.
Normally, the AC pressure on the low side should be around 30 to 40 PSI, and the high side should be above 200 PSI. But this depends a lot on the relative humidity and temperature around!
So, you will need much more information to understand if your AC is working correctly. That’s why this article created a complete guide about the proper AC pressure range with proper charts you can follow.
What Should AC Pressure Be With Engine Off?
The AC pressure should be within the normal range for the ambient temperature when the engine is turned off because the engine spreads the refrigerant and cools the air in a car’s AC system.
So, if the engine is off, this spreading of refrigerant does not happen, and the pressure stays fairly stable. Also, the air compressors in the AC system do not run with the engine off.
However, the normal range of AC pressure varies greatly! So, it is tough to give a singular answer. But do not worry because we created a pressure chart of the AC while your engine is off that you can follow.
| Temperature | Low Side Pressure | High Side Pressure |
| 70° F or lower | 25-30 PSI | Around 180 PSI |
| 70°-80° F | Around 30 PSI | 175-210 PSI |
| 80°-90° F | 35-40 PSI | Around 210 PSI |
| >90° F | 40-50 PSI | 210-225 PSI |
As you can see the numbers vary a lot depending on the temperature of your surroundings or ambient temperature.
What Should Auto AC Pressure Be With Engine Off? Factors Affecting AC Pressure
As a general rule, the auto AC pressure with the engine off should be around 25 to 40 PSI and more than 200 PSI on the low and high sides, respectively.
However, several factors can affect the AC pressure of your vehicle. This depends on the age of the vehicle, usage, the area you live in, and many other things. So, you must know a little bit about these factors to understand AC pressure with engine off.
Let’s discuss some of these factors below-
Temperature:
In normal temperatures, the AC pressure remains in the normal range. But, as the temperature increases, AC pressure also increases.
Age:
Over time, the components of the AC system can wear out, leading to reduced efficiency and potentially affecting the pressure.
Leakage:
Leakages in the air pressure system can also reduce efficiency by reducing the air pressure. So, if your AC pressure is lower than the normal range, you should look for leakages in the AC system.
Refrigerant Level:
R134a refrigerant is the most common type in today’s vehicles. However, if you’ve got an older model, especially older than 1995, you can also have freon or R12 refrigerant.
The refrigerant level can also cause the AC pressure to change. If the refrigerant is below normal, the pressure will drop, causing your AC to overwork.
However, it is also worth mentioning that the AC pressure will vary depending on whether the engine is running. Because when the engine is running, the compressor will also be turned on, increasing pressure in the system.
So, what should AC pressure be with compressor off? It should be around 25-40 PSI on the lower and around 200 PSI on the higher sides. When the compressor runs, the AC pressure should be around 40 PSI on the lower side and about 220 PSI on the higher side.
What Pressure Does Car AC Run At?
If measured correctly, A car AC should run at 40 PSI on the low and 220 PSI on the high side. But this can vary depending on the ambient temperature of your area.
Although we have been talking about AC pressure with the engine off, generally, it is not ideal for checking your AC pressure with the engine off.
You should turn on the engine, idle it at 2000 rpm, and ensure it is warm. Then, you can check the AC pressure of your vehicle.
You can follow the ambient temperature-pressure chart in this article to check if your AC pressure is at the ideal level. However, there can be several issues that you may face.
If the low and high side pressures are lower than normal, your car AC system is probably low-charged. But if the low side pressure is low, but the high side pressure is high, that usually indicates a blockage in the system.
Another problem you may face is that the low side pressure is high, but the high side pressure is low. This indicates a faulty reed valve in the compressor. Also, if both side pressures are high, your AC system is high-charged.
Although you can probably fix some of these issues yourself, we recommend you contact an auto AC mechanic if you face these issues.
As car AC systems are very intricate, and if you damage something unknowingly while trying to fix the system, it can be potentially dangerous or cause you a lot of money to fix later!
Frequently Asked Questions (FAQs)
What should be the low-side AC pressure with the engine off?
The low-side AC pressure should be around 25 to 40 PSI with the engine off. Although this varies depending on the ambient temperature, you should check the AC system for leakages if the pressure levels differ too much.
What is the correct AC pressure on a car?
The correct AC pressure range depends on your ambient temperature and whether your engine is on or off. When the engine is off, the AC pressure should be around 25 to 40 PSI and above 200 PSI on the lower and higher side. We answered this topic in the article above.
What should be the AC pressure with the engine on?
The AC pressure should always be measured with the engine on. Although the readings may vary depending on the temperature, you should get around 40 PSI on the low and 220 PSI on the high side.
Do you check AC pressure when the compressor is off?
No. You do not check AC pressure when the engine or the compressor is off. You should check the AC pressure with the engine stalled at around 2000 rpm and the fan speed at MAX.
If you’re checking with the compressor off, you will get a reading where the low side is too high and the high side is too low than normal.
Conclusion
Car AC pressure should be checked regularly to ensure that the AC system works properly. A little maintenance will help you solve problems that can be a major pain in the long run if ignored.
So, we recommend you follow our guide about what should AC pressure be with engine off and check your AC pressure levels properly. Also, remember to wear masks and goggles when working with AC systems and refrigerants.
Keep in mind it is illegal to vent R134a refrigerant into the atmosphere!
Bilzik S Nas is the mastermind behind the visual charts and diagrams you’ll discover in several VehiclesBro’s content.
With a background in coding and design, coupled with years of experience as an assistant wiring mechanic, he participates in developing intricate diagrams and informative charts to enrich our content.
While Bilzik may appear unapproachable to those unknown to him, it’s just his introverted nature. His meticulous detail-grabbing ability and dedication to creating clear-concise visuals make him a key asset to the team.
