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What Causes Low Side AC Pressure Too High

One of the most common problems with AC is abnormal compression pressure. This breakdown mainly consists of two forms: Excessively high compression pressure and abnormally low compression pressure.

Of the two types above, too high compression pressure is the most common cause. So What causes low side ac pressure too high? This article outlines the most fundamental reasons and includes several directions to resolve this common problem.

What Causes Low Side AC Pressure Too High

What Causes Low Side AC Pressure Too High

Newly assembled ACs always operate at a lower compression pressure than those used for a long time. Here are a few reasons for that difference:

Adding too much refrigerant

Too high low side pressure and moist air escaping from the vents are indications that you have added too much refrigerant.

If you’re still unsure how much new refrigerant to add, you can check by spraying water over the fins while the system is running.

If the low-side AC pressure drops significantly, the cause of the pressure surge is too much refrigerant leading to system overload.

Air in the system

The AC system cannot function properly if there is any refrigerant leak or outside air leak. Because the system’s operating principle is closed, if the outside air enters the system, the AC will not be able to complete the cooling task and cause the pressure to rise.

Condenser reduces airflow.

A clogged system is also one of the causes of abnormal pressure in AC. And airflow reduction condensers are no exception.

There are several reasons for condenser failure: debris blocking the airflow, condenser fan motor failure, etc. All of the above reasons cause the condenser to restrict airflow, failing the condenser fan pressure change.

More seriously, if the condenser fan is not working, causing a leak, your air conditioning system can be seriously affected. Usually, it will be difficult for you to troubleshoot this on your own.

Fan not working properly

Car condenser fans operate at different capacities, at different speeds.

Any failure can result in the fan not cooling the system properly, preventing air from circulating as it should. It is therefore easy to understand why the pressure of the AC can be abnormally high.

How To Fix This Problem

How To Fix This Problem

After knowing the most common causes of low side ac pressure too high problems, you can follow the abnormal behavior of AC to find a way to deal with it.

Repair condenser fan

Condenser gas blockage is one of the reasons for abnormal pressure. Meanwhile, the condenser fan plays an essential role in keeping the condenser and the entire car’s air conditioning system working properly.

Therefore, when it is detected that the low side AC pressure is too high, you should check the condenser fan problem first. The OBD2 analyzer will be a valuable tool to help you with this step.

If your condenser fan is having problems, you should change the fan system. Just a slight change, but you can get more benefits in return: not only stabilize the AC pressure but also have a fan system to help cool the system faster.

Drain coolant

As mentioned, an overloaded system with coolant can cause high pressure on the low side. Although this phenomenon is most common, fortunately, the solution is not too complicated.

You just need to drain some coolant from your AC system. During the discharge process, do not forget the following notes:

  • Turn off the thermostat for safety.
  • The high-pressure valve should be slightly open.
  • For the service valve, you need to close it completely. It would help if you used specialized equipment to make sure you have completed the valve.
  • Use the lever to turn on the compressor instead of starting the car engine.

Repairing the coils of the evaporator

The cracked pipe causes an air leak, which causes a pressure surge. You have two solutions to this problem: repair or replace.

With some coils, due to a long time of use, the cracks are too severe, you have only one option: to replace them altogether.


Low side ac pressure too high is not an uncommon condition.

However, the problems surrounding this AC abnormality have never subsided. Here are some frequently asked questions that may help you in the future if you have issues with AC pressure:

What are the symptoms of an overcharged AC system?

What are the symptoms of an overcharged AC system

Based on the common signs below, it is swift for you to detect that the AC is overloaded:

  • The cooling AC is faulty, most evident because the air is only slightly cooler than room temperature, and the cooler can even blow out hot air.
  • The compressor is noisy or damaged.
  • High pressure.
  • The engine is not working efficiently, which can cause the car to slow down and consume more fuel than usual.

What happens if you over pressurize AC?

Overloaded AC will reduce both efficiency and cooling capacity. Even the temperature in the car will increase while the ability to absorb moisture will decrease. To learn more about AC abnormality, you can refer to why AC only works when driving.

More worryingly, overloading the AC can have a severe effect on the compressor. You may have to replace the entire compressor unit because you can’t drain the coolant in time, causing the system to overload.

What causes high head pressure and high suction pressure?

Simply put, when exhaust gas leaks through the piston rings of the compressor, it creates a lower head pressure during the compression of the system.

Meanwhile, because the exhaust gas leaks through the calls, the reverse suction pressure increases. This results in pressure changes in the AC.


The pressure gauge will be a valuable tool to help you check the operating status of the AC system. Therefore, you can completely detect abnormal signs of AC early.

However, with the knowledge that answers the question What causes low side ac pressure too high, you can only diagnose the AC problem encountered.

To quickly resolve the problem, you should contact a mechanic who has the tools and experience to repair your AC system.

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