skip to content

What Can Cause AC Low Side Pressure To Be Too High?

When testing an AC system, you can get a value of more than 300 psi for the low side pressure readings, which means something wrong with your AC diagnosis.

You are not the only one who has this problem. When I mention it to other technicians, they also get confused because they do not know why it happens.

This article will discuss what can cause the low side pressure to be too high and how you should go about it when you encounter such a situation.

What is the exact problem when it comes to pressure?

When we test an AC system, we want to look at the pressure readings to assess something wrong with the AC machine.

There are three important pressure readings that we should look at.

  • You want to start by taking the high side pressure readings (red-purple scale in the image above). In a healthy AC system, you will get a value between 90 and 120 psi when you take this reading. In an old R22 AC machine, you may find that the low side pressure is too high because many people add refrigerant to the system to get a good high side pressure reading.

In many cases, this is not recommended because it can cause the pressures on the other side of the system to drop below the normal operating range. In such cases, you should use a refrigerant leak detection solution and run a leak detection test before you start adding refrigerant.

  • When you take the low side pressure readings (blue scale), you should get a value between 40 and 80 psi, depending on the temperature of the evaporator. If it is around 90 F, you would expect to see a reading close to 70 psi.
  • The third pressure readings that we should consider when looking at an AC test is the suction pressure readings (green scale). This one can be important if you are purging a line first.

There are many reasons why you would want to take each of these pressure readings. However, what we want to know is whether there is enough refrigerant in the system. If the pressures are too high, then it means that the AC is overcharged.

What can cause the low-pressure side to be too high in AC?

There are several reasons on the low side pressure is too high in AC:

The most common cause of this problem is the wrong refrigerant charge, which means you must add additional refrigerant for it to work properly. Another possible reason is that the system has leaks. So if it does not cool properly or there is no cold air

Your car’s air conditioning system has two parts that are responsible for cooling your vehicle’s interior:

  • The evaporator absorbs heat from the inside of the car by turning the refrigerant into a gas, and the condenser expels heat from the system.
  • The refrigerant flows to the condenser. This refrigerant is under high pressure, so it can drive out all of its heat before returning to low pressure in your system.

If there is something wrong with the cooling system, you might notice that your AC is blowing warm air. If this is the case, it’s best to check all of your areas.

If the ac low side in your car is too high, here are some reasons why this might be happening:

1. The cap on the evaporator core may not be working properly

As long as there are no leaks in your cooling system, all of the pressure should remain at a high level. If this is not happening, it might mean that the cap to the evaporator core is not working properly.

Using a pressure gauge to measure the ac low side pressure, you can see if this is true. If you notice the pressure too high in the A/C, you might need to replace or tighten the cap on the evaporator core.

2. The condenser is not working properly

Your car’s condenser works by moving heat from your air conditioning system and into the air around it. Several parts work together to get this process done.

However, the compressor is the main part of your system because it increases normal air pressure in your air conditioning system so that all of these parts can work.

And if any one of these parts breaks down, you will have problems with your AC’s cooling capabilities. The best way to find out what is wrong with your car’s AC is to bring your vehicle in for a professional inspection.

3. The evaporator core has leaks

The high low side pressure of your car’s air conditioning system means that there might be one or more leaks in your evaporator core. Your system loses refrigerant due to the leaks, making room for more refrigerant to enter the system.

It can cause your cooling system to run constantly, which is one of the main reasons why your ac low side pressure would be too high.

When you notice that your AC is blowing warm air, check up on all its components, including the evaporator core, for any leaks. If you find out that there are leaks in your evaporator core, you will have to replace the full system because those leaks cannot be fixed easily.

4. Your air conditioning system is not sealed properly

For an AC system to work perfectly, it has to be completely sealed. If there is something wrong with your car’s AC sealing, you might experience issues like uneven cooling. If the ac low side pressure is too high, you leak somewhere.

The easiest way to check if your car’s AC system has leaked is to take off all of the hoses connected to it. You can then use a hose or container full of water to spray the hoses and the AC system itself.

If there are any leaks, you will notice that the water can get into your car’s AC system. Once you find out where the leak is, you can replace or reattach all the hoses properly.

5. The evaporator core has a hole in it

If there are holes in your evaporator core, it means that air can get into your system. It can cause uneven cooling, and if the low side pressure is too high, it means that you will have to replace the entire AC system.

6. The compressor is not working properly

If your ac low side pressure is too high, there might be a problem with your compressor. You should check the refrigerant levels in your compressor by using a pressure gauge to measure both sides of it. If there is high pressure on the high side than the low side, your system is not working properly, which is most likely caused by a bad seal.

7. Your leak detection dye is leaking out

If you have added dye to your car’s air conditioning system, you will need to check its levels periodically. If there is no dye in your air conditioning system or if the low pressure becomes too high, it means that there are leaks somewhere in the AC system.

8. The hoses are leaking

If you have already checked for any leaks using water and you did not find any, it means that there might be a leak in the hoses themselves. Check out the rubber seals and compressor clamps to make sure that none of them are leaking. It is extremely difficult to pinpoint where the leaks are coming from, so you will have to replace all your AC hoses if you want your car’s air conditioning system to work perfectly.

9. You need to recharge your system

If the evaporator core has small leaks, you might not notice any changes in cooling capabilities at all; however, if high low pressure means that you will need to recharge your car’s AC with refrigerant. The best way to do this is by taking your vehicle to a certified AC repair shop.

10. You have some mechanical damage to your system

If the low side pressure is too high on your car’s air conditioning system, it could mean that there are some major mechanical damages in one or more of its components. If this is the case, you will need to replace all of the parts on your system.

To find out the real problem of why your car’s air conditioning system is leaking, you will have to ask a certified mechanic to inspect it. If, for example, your compressor is not functioning properly or there are some holes in the evaporator core, you will be able to repair these issues by replacing the damaged parts.

If you find any leaks in your car’s AC system, you will have to repair them before recharging the refrigerant. However, if your system is leaking out dye or has some major mechanical malfunction, you will need to consult with a certified mechanic for further inspection.

Once the proper issues are determined, they can be repaired, and the refrigerant levels will get back to normal. As a side note, it is advised that you do not attempt to repair your car’s AC system yourself if you have no prior experience with repairing or recharging air conditioning systems.

If you have never dealt with an air conditioning system before, it would be best to take it to a certified mechanic, as it can be quite tricky to repair or recharge one on your own.

Frequently Asked Questions

What does it mean when the low side pressure is too high?

It means there is some problem with the condenser fan. After the compressor, the condenser is the next important component in the AC system. It is responsible for reducing the high pressure and temperature by heading up to the expansion valve.

If there is an issue with the condenser or the condenser fan, it will not cool the refrigerant sufficiently. It leads to high pressure on the l even after it passes through the refrigerant.

What would cause AC high pressure?

When there is limited or no airflow in the condenser of your AC system or if it is an overcharged system, under both situations, the AC’s low side pressure is too high.

How do you release pressure from low-side AC?

By releasing high pressure on the low-side AC, you are attempting to find out where the leaks are coming from, leading to further repairs. You can use an aerosol spray, but if there is just one leak, it means that spraying it could be useless.

If your car’s air conditioning system has no leaks and it still seems like the compressor is not kicking in or it won’t cool down the inside of your vehicle, then you might have a different issue on your hands.

Does adding more refrigerant lower pressure?

Yes, but this will only work temporarily. Adding more refrigerants could equalize the difference between the low side and high side pressures to work efficiently.

Is the AC system working if the high side pressure is too low?

No, it’s not because you need to increase the refrigerant levels, so there isn’t any loss of refrigerant in the air conditioning system. It will also help this cause even distribution of refrigerant throughout your car’s AC system.

What are the symptoms of an overcharged AC system?

A slow compressor, compression noise, struggling engine, inefficient cooling and High-pressure readings are symptoms of an overcharged AC system.

What is the average PSI for an AC system?

It depends on the car, but most cars only have about 30 to 50 PSI of pressure in their AC systems.

Website | + posts

My Name is Christopher Angels, and I am a postgraduate in mechanical engineering. Cars have always excited me as a child, and soon I decided to dive into the world of cars by pursuing mechanical engineering. I also worked as a Mechanic for over 3 years to understand Cars' anatomy and how each part contributes to its working.

Leave a Comment