AC System

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

Mike Cross
Updated Feb 12, 2024
AC low side pressure too high

Have you ever encountered your AC's high-pressure buildup on the low side? I did during my last trip. I also realized it's a common issue during hot summers. But what factors contribute to AC low side pressure being too high? 

Excessive AC pressure leads to discomfort under the scorching sun and gradual damage to the unit. Such a situation signals a significant underlying issue that requires your attention. If you are facing AC low-side pressure that is too high, my quick tips to fix them might help you.

AC low side pressure too high
AC low side pressure too high

AC Low Side Pressure Too High: Cause And Fixing

I will underline the principal causes that can cause high pressure. However, I will also give you some DIY tips to reduce the cost of your repairs.

#1 Failing Compressor

The compressor doesn't work correctly when the low-side pressure is excessively high while the high-side pressure remains low. In such instances, even if you switch on the AC, it cannot produce cold air. It's because the refrigerant cannot circulate without the compressor's function. This issue commonly arises when your AC remains inactive for a long time.

#2 Overcharged AC

There might be too much Freon gas in your system, which leads to overcharging. It results in high pressure even when the engine is off. This may also happen due to excessive oil in the air conditioning system. In either scenario, you have to release some pressure. But in most cases, it's better to call a local mechanic.

#3 Damaged Condenser Fan

A damaged fan can hinder the airflow through the condenser. Plus, if you have debris or dirt, it can obstruct your car's ventilation. These issues can contribute to airflow reduction and lead to warm air blowing out. 

Furthermore, fan problems may also result in leaks, exacerbating the issue. So when you sweat during the drive, even after switching on the AC, the hot air may come from this damaged fan.

A damaged fan can lead to increased pressure on the low-pressure side. It can further cause damage to the evaporator coil and result in leaks. The air conditioning system may require additional repairs to restore proper functionality if such damage occurs.

#4 Contaminated AC Coils and Poor Maintenance  

High pressure in your AC may be attributed to issues with the coils or piping. Potential causes include refrigerant leakage or the use of incorrect refrigerant. In cases of leakage, your AC can get air or water contamination. It ultimately increases the pressure within your AC system.

#5 The Expansion Valve Has Failed

The expansion valve, positioned close to the evaporator, regulates the coolant flow within the AC machine. Depending on the coolant flow rate, this component may either overheat or freeze. It may lead to system damage and, subsequently, high pressure.

How to fix it?

Now that you have understood the major causes behind the issue let us focus on a few tips that can save you. These are simple DIY techniques that will help you reduce your repair cost. 

Check Your AC Pressure

Testing AC pressures is straightforward with the help of a reliable set of gauges. You need to be aware of the appropriate pressures for your vehicle. You can easily find them in the service manual. You can get the specifications online in the vehicle's documentation if you don't have access to the manual.

Here are four steps to check your AC pressure:

  • Get a Pressure Gauge: Do you have a pressure gauge? If not, then get it for this task. You can purchase it from a local store or online. It typically ranges from $30 to $50 in retail stores.
  • Connect the Gauge to the Compressor's Low Side: Calibrate that Gauge and connect it to the compressor's low side. Make sure you do it before starting your car. Alternatively, connecting the pressure gauge to the compressor's high side is also acceptable.
  • Turn on the AC and Record the Reading: After you connect the Gauge to either side of the compressor, activate your air conditioner to its maximum setting and note the reading displayed on the Gauge.
  • Refer to the Vehicle Manual: With the vehicle's manual available, compare the gauge reading to the pressure specified for your car in the manual. If your vehicle's air conditioner is experiencing cooling issues, you may find that the low-side pressure reading is excessively high.

How Can You Release Pressure From Low Side AC?

While there are methods and procedures available for releasing the pressure, this task may involve some risks. It's better to have someone experienced by your side while releasing the pressure. 

Incorrect actions could complicate issues and lead to more significant costly problems within your AC. But before you seek professional assistance, try to release pressure with these simple tips.

Follow this step-by-step process for releasing pressure from the low-side AC:

Lower the Thermostat Setting

Lowering the thermostat setting helps cool the engine. It will prevent overheating and mitigate potential mechanical complications in your vehicle.

Try Connecting the Suction and AC’s Low-Pressure Side

Connect the low-pressure side and the suction side to facilitate the extraction of excess pressure from AC’s low-side.

Close the Service Valve Prior To Pressure Release

You can use a hex key to close the service valve on the high-pressure side partially. It will prevent a complete shutdown.

Try To Activate Your Compressor and Release Pressure

Try using a jumper to get the compressor started. It will avoid the car's ignition and release the pressure systematically. Continue until all pressure is alleviated before disconnecting the components.

It's Time To Disconnect the Compressor

Once you successfully release pressure, disconnect the line that connects the low-pressure side of your compressor to the suction line. Then, you can open the service valves.

AC’s low side pressure to be too high
AC’s low side pressure to be too high

Is it my evaporator coils?

It is possible that your car’s evaporator coils are cracked and leaking and this is why your pressure readings are off. In this case, you will need to take your car to a mechanic for repairs. If you have a problem with the coils in your car’s AC system, that could also cause icing. The icing can then cause a problem with the pressure by blocking the flow of air.

Could it be a problem with the condenser fan or fan motor?

The condenser fan in your car’s AC system does operate at different capacities and different speeds. It is very possible that any kind of malfunction with the condenser fan would reduce its speed and also its efficiency. This in turn, will result in the inability of the fan to cool the system properly and allow proper airflow.


If your AC requires extensive repairs, especially in case of a leak, you might need professional help. The exact reason for the leak will determine your repair cost. Sometimes, the technician may also suggest replacing the parts.

Mike Cross
Life is too short to drive with stock audio

Leave a Reply

Your email address will not be published. Required fields are marked *

One comment on “What Can Cause AC Low Side Pressure To Be Too High?”

linkedin facebook pinterest youtube rss twitter instagram facebook-blank rss-blank linkedin-blank pinterest youtube twitter instagram