AC Pressure Too High: What You Need To Do

The air conditioner made a remarkable change to everyone’s lives when it first came on the market. It allowed a person to regulate the temperature in homes and offices, allowing everyone within to stay cool on hot days.

When air conditioning was added to vehicles, though considered a luxury, meant people could drive on even the hottest or most humid days without breaking into a sweat. Today, air conditioning is a common feature in vehicles. But what happens when you find the AC’s high side pressure too high? If this happens, you should understand how to diagnose and repair it.

The Importance of AC Readings

Car air conditioners are delicate pieces of equipment. The main function of an AC system is to remove hot air and humidity. Adding cool air is a by-product of this function. Your car’s AC system can develop issues, especially in the low and high-pressure lines.

High low AC pressure readings can develop. At first, they may not pose any problems to your car’s performance. Over time, if you continue to ignore these issues, your AC system will deteriorate.

Driver adjusting the AC system.

AC readings refer to the pressure readings of your car’s air conditioning system. They reveal if the AC unit is working correctly or not. The readings can detect damage to the system. If the temperature readings rise above normal levels, there is likely an issue with the AC.

Your car’s AC unit needs to stay within a certain pressure range. If the pressure gets too high and continues at this level, it will eventually cause compressor failure, which is expensive to fix.

Problems with AC Pressure

Car AC systems have a pressure switch. It is located on the high and low sides of the system. This switch regulates refrigerant pressure levels. There is a low and high side switch.

Pressure switch inside a car’s engine.

These switches monitor for issues with pressure. When the pressure decreases too much, it may mean there is not enough oil in the system. If the pressure is too high, the compressor could overheat. When the pressure becomes too high or too low, the switch on that side will turn the compressor off to avoid further damage.

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Symptoms and Causes

Your car’s AC system will show symptoms when there are problems with pressure levels.

Here are four symptoms and the possible AC pressure issues they may cause:

AC System Cuts On and Off Too Often or Quickly

AC systems normally cycle on and off continuously. The AC will turn off when it hits the right temperature or pressure. But if the system is cycling too often or faster than usual, it could signal that the cycling switch is broken or malfunctioning.

Inability to Cool Inside

When one or multiple pressure switches break down, the system can’t maintain the right pressure. If the pressure is off, the system won’t produce enough cold air to properly cool the inside of your car. It may take longer to reach the temperature you want, and in severe cases, the proper temperatures will never be achieved.

Compressor Staying Off

Switch failure can also keep the compressor from turning on. This is because the switches have the additional task of managing the on/off controls of the AC compressor. The compressor filters the refrigerant through the system, so if it is no longer functioning the system will stop working too.

Detail of the engine fragment with AC compressor.

Distortions and Leaks

Elevated pressure within the condenser fan of the AC can lead to distortion of aluminum and leaks from evaporator coils. There are two main reasons that cause the air pressure in the AC to exceed normal levels.

  • The first reason is the condenser is receiving partial airflow or no airflow at all. This could be due to the condenser fan malfunctioning. Make sure there is no debris blocking the airflow through the fan.
  • The second reason for higher than normal pressure readings is the system is overcharged.

AC pressure switches play an integral part in monitoring and managing the operations and services of the AC system. If you notice any of the above or other issues, assess and take care of them right away. If you think one or more switches are broken, get them replaced by a professional mechanic.

Problems with the AC System

A too high or too low-pressure reading when the car is turned off indicates problems with the AC system. Or there may be issues with specific parts within the system.

Here are three main problems to look out for:

Overcharged System

Excessive high-pressure readings on the low side can be caused by an overcharged AC system. Overcharging happens when there is too much refrigerant or oil in the system, which leads to pressure build-up. Only add refrigerant or oil to the system when it is low and make sure to insert the correct amount (check your car’s manual for specifics).

Car refrigerant valve.

Condenser Fan Problems

Dirt and debris can build up over time in the condenser fan. Too much will restrict or completely block the airflow that comes through the motor and impair the AC’s ability to cool down. Condensers performing at high pressures can damage the aluminum, which can lead to leaks in the evaporator coils.

Inspect lines, hoses, and the compressor for signs of refrigerant and oil leakage. Replace any parts as necessary. Checking for leaks will help decrease the chance of overcharging the system. You can purchase a kit to help you find leaks.

Faulty Condenser

Car AC condensers mostly absorb high pressure and temperatures from the compressor. The condenser was made to remove heat and decrease the temperature of the refrigerant. Malfunctions and damage to the condenser cause it to mismanage the pressure produced by the AC.

Broken AC condenser.

This can lead to high pressure within the low side of the system whether the engine is off or on. To find out if this is a problem, test the AC with the engine turned on.

Other Issues

High-pressure readings on the low side indicate the condenser is cycling improperly. It is either cutting in or out too quickly. This can also be caused by a malfunction in the thermostat switch. It may give off wrong temperature readings.

Adding too much refrigerant can lead to issues with temperature, the condenser, and other parts of the AC system.

To properly diagnose the issue, check the readings for the AC’s low and high pressure.

Pressure gauge for auto air conditioner.

Here are some simple steps for checking the AC system with a pressure gauge:

  1. Measure the pressure while the engine is off. If the gauges on the high and low pressure sides read more than 150 psi, the system may be overcharged. Your car’s manual will explain what the correct pressure reading should be.
  2. If the pressure is extremely low or reads zero, there is little or no refrigerant left in the system. Check for leaks.
  3. While the car is turned on and the AC set to high, check pressure lines. The low side should read at least 30 psi and high pressure should read at least 250 psi. Low and high pressure will cycle between each other. Wait for the clutch to engage to get reliable readings.
  4. Unreliable readings while there is pressure on the high and low sides indicate a part of the AC system is damaged or malfunctioning. Issues with compressors, clutches, and expansion valves can cause readings to be off.
  5. You should add refrigerant when you get low pressure readings while the car is off. Make sure all other parts of the AC system are in working order. Then add the right amount of refrigerant (consult your car’s manual if you are unsure how much to put in).
  6. If the pressure needs to be released, call a mechanic.

How Do I Get the AC Pressure Down?

If you want to repair an AC pressure issue, you need to inspect the AC system and find what, specifically, is wrong and what the cause is. Always take measurements with the car off and make sure the AC has not been used for at least one hour. This will help the pressure equalize, allowing for reliable readings.

The best thing you can do is to carefully inspect the AC system before starting any repairs. Take your time and understand every step before you make any decisions. Being prepared will save time and money in the long run.

  • First, remove the expansion valve, drier, and compressor. Inspect the expansion valves. Remove the evaporator to get a better look at the valve. If the valve is dirty gently wash with water. Make sure you don’t get water in the pipes. Last, wrap the expansion valve in thermo- insulated material with glue or packaging material.
  • Next, flush the system of any dirt and debris that has built up over time. You can achieve this by spraying AC flushing compound into the AC’s pipes. Let the compound sit for 20 minutes, then remove it with an air compressor. Last, check the pressure readings again with the engine off.
💡 If they are still high, a part of the system may need repairing.

What Should High Side Pressure Be?

For an efficiently running AC system, the low side pressure should measure around 30 psi at normal temperatures up to 90 degrees Fahrenheit. The high side pressure should measure roughly double the ambient temperature with an added 50 psi. R-134a is the most common type of refrigerant used in modern cars. You can use this type of refrigerant in older models by attaching an adapter.

The R-134a kind of refrigerant is usually a gas. It becomes a liquid when it is compressed and pressurized. The compressor in your car turns refrigerant into the liquid R-134a that runs through the AC system. The liquid refrigerant is filtered into the evaporator coil, then pumped through a valve responsible for decreasing pressure.

💡Here the refrigerant boils and evaporates into a gas. Heat is removed, leaving cool air.

If you use R-134a refrigerant in your car’s AC system, the ideal range for the low-pressure side of the system is between 25 and 30 psi or 1.3 and 2.1 Bar. High-pressure readings should range between 200 and 250 psi or 13.8 and 17.2 Bar.

Readings will vary from car to car based on the manufacturer, make, and model. The ideal refrigerant pressure will be maintained when the inside of your car stays at an ambient temperature ranging from 22 degrees to 202 degrees Fahrenheit. The best running pressure at the lower end of these temperatures should be around 22 pounds, and at the highest temperature at 57 pounds.

To test whether the high and low side pressures are in the normal range, start your car and turn on the AC system. Do a visual check to ensure the compressor is running properly. Listen for a click when the AC is running, and make sure the center hub is turning. Then look at the pressure gauges. The low side pressure should decrease and the high side pressure should increase.

Once the system has been on for a bit, increase the RPMs to around 1500 RPMs. If the ambient temperature in your car stays between 70 and 80 degrees Fahrenheit, and both pressure sides read in the ranges listed above, then you are good to go.

💡 Remember that the pressures will increase and decrease as you turn the temperature up or down while you drive.


Turning the AC on in your car and setting the right temperature is one of the first things you do once inside. When your car’s AC is not working properly, there may an issue with the high side pressure levels. Excessively high-pressure readings on the high side signify issues within the AC system, including an inability to reach cool enough temperatures, leaking of oil or refrigerant, or compressor damage.

If caught soon enough, these problems can easily be fixed. If they persist, you may need to contact a professional for help. Please leave a comment if you have any questions.

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About Matthew Webb

Hi, I am Matthew! I am a dedicated car nerd! During the day, I am a journalist, at night I enjoy working on my 2 project cars. I have been a car nerd all my life, and am excited to share my knowledge with you!

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