AC Low Side Pressure Too High (Causes and How to Fix It)

High-pressure build-up on the low side of auto ACs isn’t uncommon. However, it’s a situation you don’t want to encounter, especially during the hot summer season.

What causes the AC low side pressure to get too high, and how can you fix it? Please read along to find out.

What Does It Mean When AC Low Side Pressure Is Too high?

AC low side pressure getting too high means that the system can’t generate the needed temperature to cool down the vehicle. This situation could be related to several possibilities. It could be something to do with the compressor or refrigerant added to charge the AC or even a leak in the system.

Before getting deep into the causes, it’s only prudent to touch on an AC system’s low side and high side.

What Is the Low Side of an AC System?

The low side is the line connected from the compressor to the evaporator. On most vehicles, it has a colored cap, blue or black, that you must remove when recharging the AC system. The low side tube/line usually has a larger diameter than the high side tube.

What Is the High Side of an AC System?

The high side connects to the compressor from the bottom and is usually warm if touched. It’s also referred to as the discharge line since it’s through this line that the pressure departs the AC compressor in liquid form. The high side has a red cap.

What Happens When AC Pressure Is Too High?

When the AC pressure is too high, the interior temperature becomes too hot to survive on a sunny day. This situation indicates an underlying issue with the unit, and it’s slowly getting damaged. The first part that may fail is the compressor, which is very costly to repair or replace. You must correct the situation the first time you notice it to avoid further damages.

How to Check Your AC Pressure

Here is how you can check your AC pressure:

  1. You need a pressure gauge to help you carry out this assignment. Buying one isn’t that expensive, costing between 30-50 dollars in the retail market.
  2. Once you have the gauge, connect it to the compressor’s low side before you can turn on your car. Connecting this pressure gauge to the compressor’s high side to get the pressure readings is still okay.
  3. After connecting it to either side of the compressor, turn on the AC to the maximum and record the gauge’s reading.
  4. Now, with the vehicle’s manual at hand, you can compare the reading on the gauge to the pressure rating for your car to see which side is too high. But if your vehicle’s air conditioner has cooling problems, you’ll discover that the reading from the low side pressure is too high.

What Causes High AC Pressure?

There are several causes of high air conditioner pressure. The two main ones are:

  • A limited airflow or no airflow is passing through the condenser due to blockage
  • An overcharged air conditioner

Here are the reasons your vehicle is experiencing high AC pressure.

a.   Issues With the Condenser Fan

Since the AC’s condenser fan works at different speeds, an issue associated with this part may reduce its pace and efficiency. The result is the condenser fan being unable to cool the AC system and pass enough air effectively.

b.   Overcharging

Overcharging, in this case, has nothing to do with the electrical system but adding too much coolant or refrigerant to the AC unit. To be sure that the overcharge is causing the high pressure, you must measure the system’s pressure.

It’s advisable not to add more coolant or refrigerant to the system when the pressure is too high to avoid damaging the evaporator core.

c.   The Expansion Valve Has Failed

The expansion valve, located near the evaporator, controls the coolant flowing through the AC system. This component could either overheat or freeze depending on the amount of coolant flowing, causing damage to the system hence the high pressure.

d.   AC Coils Could Be Contaminated

The AC coils or the piping system could be why there’s too high pressure. Perhaps there’s a refrigerant leakage, or you’ve added the wrong refrigerant to the system. In the case of a leakage, the air or water produced could contaminate your AC system, leading to too high pressure.

e.   Blocked Condenser

There won’t be sufficient airflow to cool the refrigerant system if there’s a blockage on the condenser by dust or any other debris from the road.

f.     Bad Compressor

Without the compressor, the AC system’s refrigerant can never circulate, so you don’t get cold air even when the system is on. Usually, this happens when you don’t run your AC system for an extended period.

How Do You Release Pressure From Low Side AC?

Though there are ways and steps you can follow to release pressure from low side AC, this work should be left to professionals only. Any wrong action could lead to a bigger and more costly problem to the AC system. Taking your car for pressure release could be expensive, but it’s right.

Here are the steps to release pressure from low side AC if you’re a DIY enthusiast.

a.   Turn the Thermostat Down

Turning the thermostat down cools the engine so it doesn’t overheat. In turn, you avoid further mechanical issues with your vehicle.

b.   Form a Connection Between the Suction Side and the Low Pressure Side

Connecting the low pressure side to the suction side of the compressor helps in sucking out the excess pressure from low side AC.

c.   Close the Service Valve Before Releasing Pressure

You can use a hex key or a wrench to close the service valve on the high-pressure side but don’t close it entirely.

d.   Activate the Compressor, Then Release the Pressure

Use a jumper to activate the compressor instead of starting the car to release the pressure. Do it until all the pressure from the low side AC is out before disconnecting everything you used.

e.   Disconnect the Compressor

Now, after releasing the pressure from the low side AC, disconnect the line connecting the low-pressure side of the compressor to the suction line. Finally, open the valves.

How Much Will It Cost to Fix the AC Pressure Problem?

If it’s an issue with the condenser fan and you must replace the component, it may cost you 300 to 450 dollars. The larger part of the money will cover the AC parts, while labor costs 75 to 125 dollars.

In case of leaks and regassing, expect the cost to rise, but it would be hard to estimate the expense until the work is complete.

The AC pressure problem repair requires special refrigerants and tools that you may not get without the help of a professional.

Where to Have Car AC Diagnosis

A licensed mechanical shop is the best place to take your car for AC diagnosis. Some of the AC diagnosis centers include:

If you must conduct the diagnosis yourself, ensure you refer to the service manual to get the specific diagnostic according to your vehicle’s model.

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Author: Dave Johnston

Dave Junior is a hands-on automotive technician with experience in performing service, diagnostics, and repairs on domestic and imported vehicles. He enjoys writing and sharing his knowledge far and wide.

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