What Will Causes Low Side AC Pressure Too High?

Learn how to troubleshoot your issue of ac pressure

The problem of air conditioner compressors suddenly building up pressure on the low side is very common.

Any workshop you refer to may already have had dozens of vehicle owners who have this problem. The problem is frustrating too, especially in the hot summers.

Now, the question arises, what causes low side ac pressure too high?

The most reported reason for this issue is the condenser, the part that cools down the air. The problem occurs when the condenser moves through its cycles quicker than it should. This helps in building up the pressure on the low side.

If you have confirmed that this is the issue, you need to get it checked and repaired by a professional. This article will further elaborate on the problem so you can take the appropriate measures.

Checking The AC Pressure

Before you draw any conclusions, the first thing you should do is check the air conditioner pressure. The pressure checking will get you the confirmation you need that it is indeed the pressure that is too high and causing the issue.

  1. To check the pressure of an air conditioner, what you need to do is that you need to buy a pressure gauge. This is a relatively inexpensive piece of hardware that costs anywhere from $30 to $50. You can go for more expensive ones, but a cheap one, in this price range, is more than suitable for the job.
  2. You have to connect the gauge to the low side of the compressor and then turn on the vehicle. Turn the air conditioner on to maximum power and then check the pressure on the gauge. You can also connect the gauge to the high side of the air conditioner and take the reading from there too.
  3. The next step is to take your vehicle’s service manual and compare the readings. If your AC has cooling issues, then you will most probably find the pressure on the low side to be high.

Check this video if you would like to learn about this topic:

The Function Of The Compressor

Before you begin, you may have a vague idea of how the air conditioning system works. I will be detailing the work of the compressor as it is the part that does almost everything.

It is responsible for, as is evident by its name, compressing the coolant that is in the engine.

This repeated cooling of the coolant creates two pressure sides, which are the ones that show symptoms if something is wrong. The compressor increases the pressure by compressing it.

It is then released, where it is sent to the condenser for cooling. The whole process repeats itself, and hence the two pressure sides increase.

Pressure Range Of The Air Conditioning System

There are many vehicles out there whose service manuals are not available online or anywhere else.

For those people, it becomes difficult to ensure if the pressure is correct or not. Well, worry not as I have mentioned the average pressure that should be present in the compressor.

The gauge on the low side should give you a reading of anywhere between 25 to 230 pounds per square inch. The temperature of the environment should not affect the pressure too much.

So, you can expect a reading in this range when the air conditioner is working properly. If the pressure is greater than this range, then you have to get it fixed as soon as possible.

Although the focus of this article is for the low side only, I will be mentioning the pressure range for the high side only.

The range of the reading is 200 to 250 pounds per square inch. The high side can have low pressure but not more than the mentioned range, even when there is an inconsistency.

The Readings Are Out Of Range

The first thing that you need to do is not panic. This is a common issue and can be fixed. If the pressure on the low side is near or above 100, and it is 150 for the high side, then there is indeed something that is causing this imbalance in the system.

In this case, it is recommended that you don’t use the AC at all as the compressor may get damaged. Plus, an air conditioner with a pressure inconsistency does not cool either, so there is no point in turning it on.

Why Does The Pressure On The Low Side Go Too High?

Let’s talk about the main problem, the one which many of you opened this article for.

If the pressure on the low side is high while the high side is within the correct range, then the problem is most probably the condenser. I mentioned this in the introduction, but the issue will be elaborated upon even further over here.

The condenser goes through a cycle in which it performs all the required jobs to cool the air and send it to the cabin. Each process has a set time interval in order to maintain pressure and stability. Sometimes the compressor goes through the cycles very quickly.

This causes pressure to build upon its low side. But, with a system that is as delicate as the air conditioning system, there are many factors one must consider before drawing conclusions.

It is recommended to get the inspection done from a dealership or a workshop as they can pinpoint the issue.

What Is The Reason For The Pressure On The High Side Being Too Low?

Normally, only one of two things happens, either the low side has too much pressure, or the high side cannot retain it. But, in case there is a pressure issue on both sides, then there is a very high probability that the compressor, itself, has failed.

The issue can also be related to the pressure switch too. It is designed to provide power when the pressure on the high side gets too low. If it fails, then the pressure of the high side will not increase.

Both these issues cannot be diagnosed at home, so you need to spend an inspection fee to confirm that this is the problem.

Why Does The Compressor Have This Issue?

This section is linked directly to the previous one. A compressor cannot suddenly, by itself, start to decrease its cycle times, right?

Yes, that is true. The reason for it to act erratically is the thermostat or the temperature gauge. The thermostat controls and manages the temperature, while the gauge is the one that collects and measures it.

If they become faulty, the incorrect readings and adjustments can cause the compressor to malfunction. Yes, the compressor is not the one that is always at fault.

The air conditioning system is quite a complex one. One issue can result in collateral issues. So, a proper diagnosis is the only way to go if you or the mechanics are unsure of the origin of the problem.

Reasons For High Pressure When The Engine Is Switched Off

There are two possible reasons for the low side of the compressor to have an increased amount of pressure than normal, even when the engine is not working. Both of them are quite serious, so you should read this section of the article in its entirety.

1. Problems With The Condenser Fan

The condenser fan in an air conditioning unit is essential for its functioning. It has been designed to cool down the entire system, as it tends to get pretty hot while cooling the air.

So, there is a possibility that either the air from the condenser fan is being blocked by debris, or the fan has sustained damage somehow. Both of these scenarios require immediate attention because if they are not attended to, you may risk irreversible damage to the entire air conditioning system.

If the condenser fan is under too high pressure, the aluminum can distort or warp. This may cause a leak from the evaporating coil. So, this issue needs to be fixed as soon as possible.

And, you should definitely not use the AC until after the appropriate repairs are done, or else you risk further damage to the system.

2. System Is Overcharged

The term overcharged, in this scenario, does not mean that there is an electrical problem. Instead, it refers to the over pouring of the oil or the coolant in the engine. If you have put more fluid than the recommended amount, then the engine will indeed have too much pressure.

In order to reduce the pressure, you have to visit a mechanic as soon as possible. The air can also get into the coolant system, but the chances of that happening are low.

3. Failing Expansion Valve

Another reason for the issue can be a failing expansion valve. The valve is near the evaporator, and its job is to control the flow of coolant in the air conditioning system.

It is quite sensitive to the amount of coolant that is in the system. It could freeze or even overheat, which may cause damage. If the valve fails, you may expect the pressure to get uneven.

Things To Check Before Repair

There are some things that you need to check before paying for any repairs. If a mechanic is charging you a repair fee without looking at the issue, you may be a subject of a potential scam. You need to get your vehicle checked somewhere else.

When you find the right person, you need to get the pressure switch, the expansion valve, and the compressor clutch checked thoroughly. The switch and the expansion valve are located close to each other, so they are easy to access.

The switch’s functionality can be tested using an ohmmeter. If it is giving the wrong readings, then it is the culprit possible for the high pressure on the low side. If all of them check out, then, unfortunately, the only thing you can do is get the whole compressor replaced.

And let me warn you, the repair is not cheap. It will cost you, and you have to get it done unless you want to drive your vehicle without an air conditioner.

Repair Options

So, you have finally identified the issue with the air conditioner, and now you are looking to get it fixed. There are a few different paths that you can take in this matter.

Let me explain all of them, so you can know which one you can go after:

If you are in doubt and have not confirmed that there is a condenser issue in the engine, then you need to get the vehicle to a mechanic as soon as possible. And don’t forget to get turn off the AC, or you may be looking at a full replacement of the air conditioning unit.

Before you ask, issues like imbalanced pressure in the system, gassing the system will not help in any regard. It may even cause further issues, as the pressure on the low side may increase even further.

YouTube is also not helpful in this case because there is no way you can fix an issue like this one using household tools. However, it may be helpful when you need to diagnose the issue.

If any videos claim to solve the problem using basic tools, they are most probably faking it. It is better not to take your chances using such methods.

1. Condenser Fan

The condenser fan in the air conditioning system of a vehicle is vital for its proper functioning. It works at different speeds, which means it adapts to the workload. If the AC is turned on at full blast, then the fan will work at full speed. I think you get the idea.

So, what happens when something hinders the fan from working properly? The first thing is that the cooling system will overheat very quickly.

The fan is the only thing that keeps it cool. It is overheating means that you not only risk irreparable damage, but the air conditioner will also blow cool air.

So, how can a person confirm if the fan is not working properly or efficiently? The best and the cheapest way to diagnose the problem is an obd2 scanner.

The scanner plugs into the OBDII port and scans for all issues in the engine. If there is a problem with the fan, then it will definitely show that.

In cases like this, it is recommended to change the fan completely. It does not cost a lot, and a newer one will definitely be better than the older one as it may run faster and may help cool the system quicker.

2. Coolant Discharge

If the issue is related to there being too much coolant in the system, then the steps are not that difficult. There are a few things that you can do to discharge some of the coolants from the air conditioning system:

  1. Turn off the thermostat.
  2. Bridge a connection between the suction side of the compressor to the low-pressure side.
  3. Fully shut the service valve using a wrench or, more preferably, a hex key.
  4. Close the high-pressure valve but leave it open a bit.
  5. Instead of turning on the vehicle, use a jumper to turn the compressor on.
  6. Let the process complete until the low-pressure side is completely unpressurized.
  7. Disconnect everything and open the valves.

If you are a vehicle enthusiast, then you may already have all the required tools at home. If not, then you should head towards a mechanic. One step, if done slightly wrong, can cause a larger malfunction in the system.

3. Repairing The Evaporator Coils

If the evaporator coils are causing the issue, then this may be due to the fact that they have cracked. It is entirely possible for a part like these to crack.

The cracking causes a leak, which in turn makes the pressure unstable. There also may be an icing issue that causes blockage in the air conditioning system, hence letting the pressure increase on one side.

If the damage is not too much, then the coils may get repaired. If they are beyond repair, then the only option you have is to get them completely replaced.

4. Checking The Pressure Switch

If you have exhausted all other options, then you may need to check the pressure switch in the air conditioning unit as I stated that the switch had been designed for turning on the supply when the pressure is too low on the high side.

If it becomes faulty and is unable to perform its job, then there will definitely be a problem with the pressure regulation in the compressor. In cases like this, you may need to get the whole switch replaced.


I hope you got the answer to the question of what causes low side ac pressure too high in this article. It is a serious issue that needs urgent attention as soon as it is noticed or observed.

If the pressure is too much on the low side, you may have to get the compressor replaced as a last resort unless you exhaust all other options.

If you are one of those readers that is going through the issue while reading it, I would advise that you don’t turn on the AC at all.

I hope the lengthy article helped you and I also hope that the repair does not cost you too much!


Written by Kane Dan

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