AC Low Side Pressure Too High – How To Diagnose And Fix It?

AC Low Side Pressure Too High – How To Diagnose And Fix It?

It’s not an uncommon problem with automotive AC systems to find the pressure on the “low” side of the compressor being too high. As a result of this, you’ll probably notice your air conditioning not working correctly. You know that feeling when you open the car door on a hot, humid afternoon, and it feels like hell itself comes bellowing out?

One of the (many) possible reasons for your AC not working is an imbalance in pressure. When the compressor’s low-pressure side is too high, it inhibits the system’s ability to cool the incoming air. In this article, we’ll be discussing the issue of why your car’s AC low-side pressure is too high. This means diving deep into how a car’s AC unit works.

Besides that, we’ll be looking and analyzing what “AC low-side pressure is too high” actually means. Moving on, we’ll then look at the respective symptoms of this issue, and what causes your car’s AC unit to go awry. Not to mention, how to diagnose and fix this issue, as well as what it’ll cost you for a professional repair.

There are additional guides, references, and resources here that you might handy for diagnosing car AC issues, too.

How Does An AC System Work

The modern AC system hasn’t changed much in the last 60-odd years. Sure, it’s considerably more efficient now, but the principles governing it are pretty much the same – a bit like the internal combustion engine.

Here’s a fundamental fact that most people don’t quite grasp. The main job of the AC in a car isn’t to push cold air into the vehicle. Instead, it’s to remove the hot air and associated humidity. Sure, adding cold air in is a by-product (as you’re trying to figure out how to make car AC colder), but it’s not the primary purpose.

Here is an example of an AC system. Have a quick watch – this video is 7 minutes long but well worth your time.

The serpentine drive belt is attached to the crankshaft – the “power output” shaft of your engine if it helps to think of it that way. This belt can drive several components, depending on how the company designed the car. These components might include the alternator, the power steering pump, and – such as is relevant to this article – the air conditioning compressor.

1. Compressor

From the compressor, two lines lead in/out. These are what we call the high-pressure and low-pressure sides of the compressor. They contain a fluid – the refrigerant.

You can tell which side is which from a quick look at your air conditioning system. The larger-diameter pipes are lower pressure. The pipes with a narrower diameter are high-pressure.

To get your head around this, it might help to compare your thinking with a hose pipe. When the nozzle is wide open – just a big hole – the water comes out slowly. It’s low-pressure. When the nozzle opening narrows, the water shoots out further with more force: higher pressure.

The compressor compresses the refrigerant gas within it by squeezing it between two points. As a result, it forces scorching, highly-pressurized refrigerant gas into the high-pressure area of the system.

2. Condenser

From here, the compressor forces the gas through a condenser. The condenser works in a way very similar to your car’s radiator. As the gas travels through this component, the temperature drops, and it turns back into a liquid.

Immediately after passing through the condenser, the liquid is forced through the dryer. The dryer ensures that the refrigerant is now entirely liquid – there are no gaseous elements to it.

3. Expansion Valve

The next component is the thermal expansion valve. This turns the hot liquid into a cold gas. Following this, the gas passes through the evaporator.

You can think of the evaporator as the central part of the system for cooling the air heading into your car’s cabin. Like the condenser or the coolant radiator, air passes through it. However, whereas these have the purpose of removing heat from the vehicle, the evaporator removes heat from the air.

The fan sucks air in towards the cabin. In the process, the air passes through the evaporator, giving you that cool, refreshing feeling as it blows out onto your face.

Following that, the cold refrigerant flows back to the compressor, where the whole process starts all over again.

AC Low Side Pressure Too High – What Does This Mean?

Air conditioning (AC) is an essential feature in most modern vehicles, providing comfort during hot weather or long drives. However, as with any system, certain issues can arise, affecting its performance. One such issue is when the AC’s low side pressure is too high. Let’s delve into the details of what this means, the causes, and potential solutions.

The AC low side pressure getting too high implies a malfunction within the system that prevents it from generating the needed temperature to cool down the vehicle. The core function of an AC system is to absorb heat from the car’s interior and dissipate it to the outside environment, thus cooling the inside of the vehicle.

This heat transfer process is facilitated by pressure changes within the system’s components.

If the low side pressure is too high, it suggests that the refrigerant cannot absorb and remove sufficient heat. The consequence is a less efficient AC system, resulting in a warmer vehicle interior than desired.

The cause could be a variety of factors. It might be an issue with the AC compressor, an overcharge of refrigerant, a leak in the system, or blockages within the AC components.

High Side Low Side HVAC

Understanding the different sides of your car’s AC system, along with potential issues like high low-side pressure, can help diagnose and potentially resolve problems with your vehicle’s cooling system. If your car’s AC system is not cooling as expected, it might be time to consult a professional mechanic to ensure optimal performance.

1. AC Low Side

The low side of a car’s AC system, also known as the suction side, primarily consists of the evaporator and lines leading back to the compressor. The refrigerant enters this side as a low-pressure gas.

The evaporator, located inside the passenger compartment, absorbs heat from the car’s interior, causing the refrigerant to evaporate. This heat absorption process cools the inside of the vehicle. The refrigerant, now a low-pressure gas, travels back to the compressor through the low side lines, ready to repeat the cycle.

In terms of physical identification, the low side line or tube typically has a larger diameter than the high side tube. Additionally, the low side port, used for recharging the AC system, is often covered by a blue or black cap.

2. AC High Side

Opposite to the low side is the high side of the AC system, which includes the compressor, condenser, and the lines leading from the compressor to the condenser. The refrigerant enters this side as a high-pressure gas.

The compressor pressurizes the refrigerant, heating it up significantly. This high-pressure, hot refrigerant then travels to the condenser, typically located at the front of the vehicle near the radiator. Here, the refrigerant releases its heat to the outside environment and cools down, transforming into a high-pressure liquid.

This high side of the system is often referred to as the discharge line, as it’s through this line that the pressurized refrigerant departs the AC compressor. This line, or port, is generally warm to the touch if the AC system is operating. For identification purposes, the high side port usually has a red cap.

How To Check AC Pressure

Now we’ve considered how the AC in your car works, let’s consider how to test its pressure.

I should point out, first of all, that you could (and perhaps should) take your car to an air conditioning specialist to have them do this job for you. It’s essential to be very careful when working with AC systems. Some parts of them are quite fragile, and making the wrong mistake could be catastrophic.

1. Find An AC Pressure Gauge And Refer To A Repair Manual

If you want to test your car’s AC pressures, it is possible to do it yourself. You should be able to find gauges on Amazon for about $50 to $100. In most situations, you won’t need to shell out hundreds of dollars for a top-of-the-range model – you’re only doing a quick, cheap check. That being said, make sure that you buy a reliable gauge.

Before starting the testing procedure, you should find out what the correct required pressures are. Some manufacturers list these in the owner’s manual. For lots of cars, however, you’ll have to look them up online. When doing this, make sure to use a factual vehicle directory rather than random people’s random guesses on a random forum.

Use the expected ambient temperature or general readings for comparison.

2. Find The Low-Pressure Side And High-Pressure Side

When you’ve got your AC pressure gauge, hook it up. The AC system has two caps on it. One of these caps is on the low-pressure side, the other on the high-pressure side. Remember that the high-pressure side of the AC has a narrower diameter and vice versa.

ac low side pressure too high
Cap for the high-pressure side of a 2005 Vauxhall Corsa. Note the low-pressure pipe passing next to it. The cap for this is in a separate location.

In your owner’s manual, there should be a page detailing which AC cap is which, as well as where to find them. On some vehicles, just accessing these ports can be quite a chore. They can be tucked away down the back of the engine block sometimes. Yep. Manufacturers do seem to just like making things difficult occasionally.

3. Check The AC Pressure Gauge Reading

The gauge usually differentiates between the high- and low-pressure hoses with colors. Blue represents low pressure, whereas red represents high pressure.

Remove the caps and attach the hoses, ensuring you put each hose on the right side. You’ll have to pull the sleeve up, push it on, and then release the sleeve before tightening it on. It’s easy not quite to attach it properly, so make sure it’s on correctly.

Now, turn on the engine and leave it for a little while. Doing this should give the system sufficient time to get the refrigerant flowing around and working efficiently. At this point, read the pressures on the gauges.

The low-pressure (blue) gauge should show something in the range of 20 PSI to 30 PSI, or 1.3 to 2.1 Bar. You should expect much higher readings on the high-pressure gauge of between 200 PSI and 250 PSI (13.8 to 17.2 Bar).

These readings will vary depending on the manufacturer, make, and model. The figures provided above are a general estimate only.

If either of the pressures is too high or too low, it indicates a problem somewhere within the AC system.

What Are The Symptoms Of AC Low Side Pressure Too High

When the low-side pressure in a car’s AC unit is too high, it can lead to various symptoms that indicate potential issues with the system. Recognizing these symptoms is crucial as it allows car owners to take appropriate action and seek professional assistance to diagnose and rectify the problem.

Here, we will explore the common symptoms associated with high low-side pressure in a car’s AC unit and discuss each symptom in detail.

  • Weak airflow from the AC vents
  • Odd noises from the AC compressor
  • High cabin temperatures
  • High AC pressure readings
  • Engine performance issues

Recognizing the symptoms of high low-side pressure in a car’s AC unit is essential for timely diagnosis and repair.

If you experience weak airflow from the vents, unusual noises from the compressor, elevated cabin temperatures, abnormal high-pressure readings, or engine performance issues, it’s advisable to consult a professional mechanic who can assess and rectify the problem to restore optimal AC functionality in your vehicle.

AC Low Side Pressure Too High, Symptoms #1: Weak Airflow from the Vents

When the low-side pressure in the AC unit is excessively high, one noticeable symptom is a decrease in the airflow coming from the vents. The air may feel less forceful, reducing the system’s ability to cool down the cabin effectively. This can make it uncomfortable for occupants, especially during hot weather.

AC Low Side Pressure Too High, Symptoms #2: Unusual Noises from the Compressor

An overcharged or malfunctioning AC system can put excessive strain on the compressor. This can result in strange noises emanating from the compressor, such as rattling, hissing, or grinding sounds. These noises indicate potential issues with the system’s refrigerant circulation and compressor operation, which should be addressed promptly to prevent further damage.

AC Low Side Pressure Too High, Symptoms #3: Elevated Cabin Temperatures

One of the primary functions of an AC system is to regulate the temperature inside the car’s cabin. However, when the low-side pressure is too high, it can affect the cooling capacity of the system. As a result, the cabin may not reach the desired temperature even when the AC is running at full blast.

The air blowing from the vents might feel warm or not as cool as expected, making driving conditions uncomfortable.

AC Low Side Pressure Too High, Symptoms #4: Abnormal High-Pressure Reading

An overcharged AC system or other underlying issues can lead to abnormally high pressure readings on the high-pressure side of the system. This can be detected by using specialized gauges to measure the pressure levels. If the low-side pressure is high, it can indicate a problem that needs to be addressed to ensure the proper functioning of the AC system.

AC Low Side Pressure Too High, Symptoms #5: Engine Performance Issues

In some cases, a car’s AC system with high low-side pressure can impact the engine’s performance. The excessive strain on the compressor can draw additional power from the engine, resulting in decreased overall performance.

It may lead to symptoms like reduced acceleration, increased fuel consumption, or even engine misfires. If these issues arise alongside AC problems, it’s crucial to have the system inspected to identify the root cause.

What Causes Low Side AC Pressure Too High

The performance and efficiency of a car’s air conditioning (AC) system are often taken for granted until it malfunctions. One such problem could be high low-side pressure in the AC system, which could result in insufficient cooling, further complicating the situation, especially in the hot summer months.

This issue might arise due to a variety of factors including a faulty AC compressor, an overcharged AC system, a defective condenser fan, and other factors. Here are the primary causes:

  • Failing AC Compressor
  • Overcharged AC System
  • Damaged Condenser Fan
  • Faulty Expansion Valve
  • Blocked or Contaminated AC Coils
  • Leaks in the System

AC Low Side Pressure Too High, Causes #1: Failing AC Compressor

The compressor, often referred to as the heart of the AC system, plays a pivotal role in circulating refrigerant within the system. When the compressor malfunctions or fails completely, it leads to irregularities in pressure.

In such instances, the low-side pressure might rise, and the high-side pressure could drop. This imbalance often occurs when the AC system is not utilized for an extended period, resulting in the compressor’s inability to facilitate effective refrigerant circulation, hence hindering the production of cold air.

AC Low Side Pressure Too High, Causes #2: Overcharged AC System

An overcharged AC system can significantly affect its performance. High pressure, even with the engine turned off, may indicate an overcharged system. This overcharge could be due to an excess amount of refrigerant or oil in the system.

It’s essential to have a professional mechanic relieve some of this pressure, as the issue will not resolve independently. The careful maintenance of an AC system’s charge is crucial to ensure optimal operation and prevent pressure imbalances.

AC Low Side Pressure Too High, Causes #3: Damaged Condenser Fan

The condenser fan is vital for maintaining the cooling efficiency of the AC system. When damaged or obstructed by debris, the airflow through the condenser diminishes, consequently leading to a rise in the low-side pressure.

This could potentially result in a leak or warm air emanating from the vents. Keeping the condenser fan clean and in good working condition is key to maintaining correct pressure levels within the AC system.

AC Low Side Pressure Too High, Causes #4: Faulty Expansion Valve

The expansion valve, located near the evaporator, regulates the flow of coolant within the AC system. If it fails or becomes inefficient, it can cause an overheating or freezing scenario depending on the coolant flow, leading to high low-side pressure. A regular check of the expansion valve can prevent such irregularities and ensure a smoothly running AC system.

AC Low Side Pressure Too High, Causes #5: Blocked or Contaminated AC Coils

AC coils can also contribute to high low-side pressure if they are blocked or contaminated. This could be due to a refrigerant leak, or if the incorrect type of refrigerant was added to the system. A contaminated or blocked coil can disrupt the normal flow of refrigerant, leading to pressure imbalances. Regular inspection and cleaning of the AC coils can mitigate these problems.

AC Low Side Pressure Too High, Causes #6: Leaks in the System

Leaks in the AC system can lead to changes in pressure levels. These leaks could occur in the compressor, condenser, or evaporator, allowing the refrigerant to escape, causing the pressure to drop. If the system is recharged without identifying and repairing these leaks, it could lead to an overcharge, thereby causing a high low-side pressure.

Regular inspections for leaks can help ensure the smooth and efficient operation of the AC system.

A/C Diagnostic

This article will consider what happens when the pressure on the AC’s low side is too high.

There are two different possible situations here.

  1. The AC low side pressure is too high, and the high side pressure is also high.
  2. The AC low side pressure is too high, and the high side pressure is too low.

Depending on what your gauges show, different problems are likely. Therefore, there may be different steps you need to take to get it fixed. Therefore, we’ll be looking at these two scenarios, in particular:

AC Low Side Pressure Too High

The high-pressure side is what comes out of the AC belt-driven compressor. If the readings here are still high – that is, within their normal operating range – it indicates that this part of the system is working correctly.

The problem probably lies somewhere in the transition between the high- and low-pressure sides.

There could be something wrong with the condenser or the condenser fan. These are the most likely issues, although that’s far from an exhaustive list.

The condenser is the first component in the AC system after the compressor. It should reduce the temperature and pressure as it heads up to the expansion valve. Suppose there’s an issue with it or the fan. In that case, it might not cool the refrigerant sufficiently, meaning the pressure is still higher than it should be after it’s passed through the evaporator.

The other potential reason for this situation is an overcharged system. When the AC system is re-gassed, every car is designed to take a certain quantity of refrigerant and oil. Like all the fluids you need in a vehicle, you have to put the right amount of them in.

It’s possible for a mechanic to accidentally put too much refrigerant or oil into your vehicle for various reasons.

The result is an overall increase in pressure in the system as a whole.

AC High Side Pressure Too Low

In this situation, where the high-pressure side of the AC is too low, and the low side pressure is too high, the problem is probably compressor-related.

It could also be related to the AC pressure switch, the expansion valve, the evaporator, or the dryer. There could also be a leak in the AC system.

The AC pressure switch regulates the flow of refrigerants through the compressor. Sensors on the high and low sides monitor their pressures. If either side is too high or too low, it should switch off the compressor to prevent any damage and keep the system working. Should these sensors or the switch develop faults, this can lead to the refrigerant pressures being too high or too low.

If the expansion valve isn’t working – or at least isn’t working correctly – the pressure and temperature will be affected as the refrigerant goes through the evaporator. As a result, the gauges might show that the system’s pressures aren’t what they should be.

The dryer’s job is to remove moisture from the refrigerant. If for some reason, it stops working or gets overloaded, it won’t be removing moisture. This moisture leads to the high-pressure side being too low and the low-pressure side being too high.

ac low side pressure too high temperature controls

How To Fix AC In Car

Embarking on a DIY journey of diagnosing and repairing your car’s air conditioning (AC) unit can be quite an adventure. Armed with just a bit of technical know-how and a will to learn, you could save yourself some extra cash that you might have spent at a garage. This guide is for those brave DIYers who notice that the low-side pressure in their car’s AC unit is higher than it should be.

A variety of issues could be causing this, from a damaged evaporator coil to an overcharged AC system. Don’t be daunted though; tackling this problem is as easy as following a step-by-step process. We’ll guide you through diagnosing the problem and then go on to show you how to fix it.

Here’s a quick list of steps to try and fix AC low side pressure too high :

  1. Park the car safely and turn off the engine.
  2. Locate the AC system under the hood.
  3. Disconnect the negative battery cable for safety.
  4. Inspect the evaporator coil.
  5. Check if the AC system is overcharged.
  6. If the evaporator coil is damaged, replace it.
  7. If the AC system is overcharged, discharge the excess refrigerant.
  8. Restart the car and check if the AC is working properly.

Now, let’s delve deeper into each of these steps.

Step 1: Park the Car Safely and Turn Off the Engine

Before getting started with the diagnostics and repair, ensure the car is in a safe, flat location with the engine turned off. Give yourself ample time to complete the repair without rushing.

Step 2: Locate the AC System Under the Hood

Under the hood of your car, you will find the AC system. The components we’re particularly interested in, such as the compressor and the evaporator, are usually located near the front of the engine, often on the passenger side.

Step 3: Disconnect the Negative Battery Cable

To prevent any accidental electrical shocks while working on the AC system, it’s essential to disconnect the negative battery cable from the battery.

Step 4: Inspect the Evaporator Coil

One of the common causes of high low-side pressure is a damaged or leaking evaporator coil. Inspect it for any visible damage or leaks. In case of damage or leakage, you’ll need to replace the coil, which can cost anywhere from $850 to $1100 for parts and labor depending on your car’s model.

Step 5: Check if the AC System is Overcharged

Another cause of high low-side pressure could be an overcharged AC system. This means there’s too much refrigerant in the system, which can lead to excessive heat and pressure and possibly damage the compressor. A telltale sign of an overcharged AC system is the AC blowing hot air out of your vent.

Step 6: Replace the Damaged Evaporator Coil

If you’ve found that your evaporator coil is damaged, the next step is to replace it. Remember, this is a cost-intensive process and may require professional help depending on your comfort with auto repairs.

Step 7: Discharge the Excess Refrigerant if Overcharged

In case you’ve determined that your AC system is overcharged, you will need to discharge the excess refrigerant. Professionals typically use vacuum devices to bleed out the extra refrigerant and bring the pressure levels back to normal.

Step 8: Restart the Car and Check the AC

After performing the necessary repairs, start the engine and turn on the AC system to check if the issue has been resolved. You might need to add more refrigerant if necessary. If the AC is working well, you’ve successfully diagnosed and repaired the problem!

With some patience, the right tools, and this guide, even complex issues like a high low-side pressure in your car’s AC system can be tackled head-on.

How To Release Pressure From The Low-Side AC

When maintaining your vehicle, it’s crucial to keep a keen eye on the various systems that keep it running smoothly. The air conditioning (AC) system is no different, and it’s particularly crucial to monitor its pressure levels. Although managing your car’s AC system might sound like a professional mechanic’s job, some of the tasks can be handled at home if you’re a DIY enthusiast.

One such task is releasing excessive pressure from the low-side of a car’s AC unit, a procedure that requires care and precision to avoid causing damage to your car’s AC system. If not handled correctly, this situation can lead to costly repairs. However, with the right steps and safety measures, you can navigate this task effectively.

  1. Lower the Thermostat
  2. Establish a Connection Between the Suction Side and the Low Pressure Side
  3. Secure the Service Valve Before Pressure Release
  4. Initiate the Compressor and Release the Pressure
  5. Disconnect the Compressor

While a car’s AC system might seem daunting to handle, understanding the processes involved can save you from potential high-cost repairs. Regular servicing and maintenance by a certified mechanic is the best way to prevent high low-side AC pressure.

However, understanding these steps allows you to tackle issues as they arise, equipping you with the confidence and capability to maintain your vehicle’s health. Here are the detailed steps to how you can release excess pressure from the low-pressure side of your car’s AC unit:

Step 1: Lower the Thermostat

The first step in releasing excessive pressure from your AC’s low side is to lower your car’s thermostat. Doing so cools down the engine, preventing potential overheating and further mechanical problems. Be aware that an excessively hot engine can compromise the integrity of other components, which could lead to additional issues.

Step 2: Establish a Connection Between the Suction Side and the Low Pressure Side

Once your car’s engine has cooled down, the next step is to form a connection between the suction side and the low pressure side of the AC system. This connection allows the compressor to pull out the excess pressure from the low-side AC. Remember to do this carefully to avoid causing damage to the compressor or the AC system.

Step 3: Secure the Service Valve Before Pressure Release

After forming a connection, secure the service valve located on the high-pressure side of the AC system. This can be done using a hex key or a wrench. However, be sure not to close it entirely. Leaving the valve slightly open will allow for the controlled release of pressure when you activate the compressor.

Step 4: Initiate the Compressor and Release the Pressure

With the service valve secured, it’s time to engage the compressor. Instead of starting your car, use a jumper to activate the compressor. This process helps to release the pressure from the low-side AC. Be sure to continue this process until all excess pressure is released before proceeding to disconnect the setup.

Step 5: Disconnect the Compressor

Once all the pressure is released, you can now disconnect the line connecting the low-pressure side to the suction side of the compressor. Following this, open the valves. Ensure all connections are safely disconnected to prevent any unintended mechanical issues or potential leaks.

AC Pressure Chart

If you’re trying to diagnose and troubleshoot an issue where your AC low side pressure too high, here’s an AC pressure chart for you to refer from. This chart represents the ideal pressure ranges for a typical R-134a A/C system in vehicles:

Ambient Temperature (°F/°C) Low-Pressure Gauge (psi / kPa) High-Pressure Gauge (psi / kPa)
65°F (18°C) 25-35 psi / 172-241 kPa 135-155 psi / 931-1069 kPa
70°F (21°C) 35-40 psi / 241-276 kPa 145-160 psi / 1000-1103 kPa
75°F (24°C) 35-45 psi / 241-310 kPa 150-175 psi / 1034-1207 kPa
80°F (27°C) 40-50 psi / 276-345 kPa 175-210 psi / 1207-1448 kPa
85°F (29°C) 45-55 psi / 310-379 kPa 225-255 psi / 1551-1758 kPa
90°F (32°C) 45-60 psi / 310-414 kPa 250-285 psi / 1724-1965 kPa
95°F (35°C) 50-65 psi / 345-448 kPa 275-310 psi / 1896-2137 kPa
100°F (38°C) 55-70 psi / 379-483 kPa 315-350 psi / 2172-2413 kPa
105°F (41°C) 60-75 psi / 414-517 kPa 330-375 psi / 2275-2586 kPa
110°F (43°C) 65-80 psi / 448-552 kPa 340-385 psi / 2344-2655 kPa

Please note that these values are approximations and your vehicle’s specifications might differ. Always refer to your vehicle’s specific service manual. Meanwhile, here’s an additional table to help you understand these A/C system pressure readings.

Understanding A/C System Pressure Readings:

Low-Pressure Gauge High-Pressure Gauge Required Action
IN RANGE IN RANGE A/C system is functioning correctly.
LOW LOW Add more refrigerant.
LOW HIGH Needs service – possible blockage in the expansion valve or orifice tube.
HIGH LOW Needs service – potential compressor malfunction.
HIGH HIGH System is overcharged. Carefully remove refrigerant. Venting is illegal.

Please remember, discharging R-134a refrigerant into the atmosphere is illegal due to environmental hazards. Always ensure that a certified technician handles refrigerants.

Cost Of Fixing AC In Car

High low-side pressure in your car’s air conditioning (AC) system is a common issue that may have several underlying causes. Often, this condition could be due to an overcharged system, a failing condenser fan, blocked condenser coils, or refrigerant leaks. Identifying the precise cause and resolving the issue can be complex and usually requires professional intervention.

While the below cost estimates provide a useful guide, it’s important to remember that costs can vary widely based on various factors, including your vehicle’s age, make, model, and the location and severity of the issue.

Always seek professional advice when dealing with AC problems to ensure you get a detailed diagnostic and a precise cost estimate. Additionally, while some AC repairs can be done at home, always prioritize safety and legality, especially when handling refrigerants.

1. Condenser Fan Replacement

One of the main culprits behind high low-side pressure is a malfunctioning or completely failed AC condenser fan. This fan plays an essential role in dissipating the heat from the condenser coil, enabling the refrigerant to condense from gas to liquid form.

If the fan fails or isn’t working optimally, it can’t effectively cool the refrigerant, resulting in high pressure. Replacing a faulty condenser fan typically costs between $350 and $500. The majority of this amount, approximately $250 to $350, accounts for the cost of the new part.

Labor is relatively less, usually around $100 to $150, as it requires less technical skill to replace. It’s important to note that these figures may vary depending on your vehicle’s make and model, as well as the garage’s labor rates.

2. System Overcharge

An overcharged AC system is another common reason for high low-side pressure. This means there’s too much refrigerant in the system, which can put unnecessary strain on the AC components and lead to a high-pressure reading.

Resolving an overcharged system usually involves safely removing some refrigerant or oil. This is a job for professionals due to Environmental Protection Agency (EPA) licensing requirements for handling refrigerants.

Depending on the extent of the overcharge, you might need to spend between $70 and $150 on labor for refrigerant removal, plus an additional $50 to $100 if the system needs to be re-gassed.

3. Detecting and Repairing Refrigerant Leaks

Refrigerant leaks can cause an array of problems in an AC system, including high low-side pressure. Leaks can occur due to small cracks in the pipes or a failing compressor, necessitating a careful diagnostic procedure to locate them.

Identifying the leak’s location can range from $75 to $400, mainly depending on the leak’s location and size. Some garages use a UV lamp and dye test to trace refrigerant leaks, which is an effective but somewhat expensive procedure. If a leak is identified and a repair is possible, the labor cost could range from $100 to $200.

However, costs can escalate quickly if parts like the AC compressor ($450-$700) or evaporator coil need replacing, and if extensive labor is needed to access these parts (such as removing the dashboard), the labor costs can rise up to $700 or even more.

How Do I Solve AC Low Side Pressure Being Too High

This kind of work is almost solely limited to professionals. While you may be able to find tutorials on the internet that show you how to do it, believe me – it’s probably not worth it.

Re-gassing or fixing an AC system requires specialized equipment and chemicals that you should need licenses to acquire. This is especially the case when it comes to the refrigerants used in your car’s AC.

And that’s before we get into all the specialist knowledge you, honestly, can’t do without.

On this occasion, you’re going to have to swallow the cost and take your car to the nearest qualified AC technician. Ring around your local shops to see who can do it and give you the best quotes.

More in-depth AC work – for example, if the technician finds a leak somewhere in the system – will cost more. It’s hard to put an exact figure on it because it very much depends on where the leak is. The leak could also be a hairline crack in one of the pipes that the technician can only find with CSI-style UV lamps.

All of this – the “finding” and the “fixing” – takes time. Even if the cost of materials isn’t too high, expect to pay somewhere in the hundreds of dollars, if not thousands. Refer to the previous section for a more detailed look at the costs.

AC Pressure Troubleshooting Chart

Automotive AC Diagnosis And Troubleshooting Chart
Low Side High Side Vent Temperature Causes (And What You Need To Fix)
Low Low Warm Refrigerant (aka Freon) charge is too low
Low Low Warm Expansion valve is stuck in its fully closed position
Low Low Warm Orifice tube has been plugged and clogged
Low Low Warm Restriction or obstruction in the high side pressure
High High Warm Refrigerant (aka Freon) was overcharged
High Low Warm Failure of either the compressor or control valves
High High Slightly Cool Air has entered the AC system, or if the Freon is overcharged
Normal Normal Warm Moisture exists in the AC system

AC Low Side Pressure Too High – Causes and Fixes

  1. AC low side pressure getting too high means that the system can’t generate the needed temperature to cool down the vehicle.
  2. The low side of an AC system is the line connected from the compressor to the evaporator and has a larger diameter than the high side tube.
  3. The high side of an AC system connects to the compressor from the bottom and is usually warm if touched.
  4. When AC pressure is too high, the interior temperature becomes too hot to survive on a sunny day, indicating an underlying issue with the unit that could cause compressor failure.
  5. Checking AC pressure requires a pressure gauge, which costs between $30-$50 in the retail market, and comparing the reading on the gauge to the pressure rating for your car.
  6. The two main causes of high AC pressure are limited airflow or no airflow passing through the condenser due to blockage and overcharging.
  7. Several issues, such as issues with the condenser fan, overcharging, failed expansion valve, contaminated AC coils, blocked condenser, and bad compressor, could cause high AC pressure.
  8. Releasing pressure from low side AC requires professional help, and DIY enthusiasts must follow specific steps such as turning the thermostat down, forming a connection between the suction side and the low-pressure side, closing the service valve before releasing pressure, activating the compressor, and finally disconnecting the compressor.
  9. The cost to fix the AC pressure problem varies depending on the underlying issue, and it requires special refrigerants and tools that professionals can provide. The cost could range from $300-$450 for a condenser fan replacement, and leaks and regassing could increase the cost.

AC Low Side Pressure Too High: In Conclusion…

High-pressure build-up on the low side of auto ACs is not uncommon, but it can cause cooling problems during the hot summer season. I hope you’ve found this article useful and that it’s given you a decent beginner’s understanding of an automotive AC system (and to find out more, check out our write-up on how long does it take for a car to cool down).

If there’s one thing to take away, I would suggest taking your car to a mechanic you trust for almost every AC issue you come across. These systems are tricky to navigate and surprisingly easy to break, so if you aren’t sure what you’re doing, it’s better to be safe than sorry.

Thanks for reading, and I hope you manage to successfully get your AC working once again.

FAQs On AC Low Side Pressure Too High

If you still have some unanswered questions, perhaps our FAQs on AC low side pressure too high might have the solution…

What Causes Low Side AC Pressure Too High

There are several reasons why your car’s AC might be experiencing an issue with low side AC pressure too high. For the most part, it could be a component failure, such as a faulty condenser or condenser fan. If either of the latter fails, the AC’s refrigerant (or Freon) can’t be sufficiently cooled, causing issues with the pressure readings. Or else, it might be a problem with over-gassing with refrigerant. The AC pressure switch might also be at fault, falsely regulating the pressure through the compressor.

How To Check Freon Level In Car

All you need to check the level is to find the AC service ports in your car (there should be two pressure service ports). You then have to attach a set of specialty gauges to measure its pressure. Now, turn on your car, set the AC to full, and let the compressor run for a few minutes. Finally, check the pressure to know your Freon levels. On the low-pressure port, it should be reading 25 to 45psi. Meanwhile, the high-pressure port should read 250 to 400 psi. If it’s lower, then you need to top up your refrigerant.

How To Read AC Gauges

One of the instruments used to measure Freon level is a specialized AC gauge. There should be two gauges, each for the two pressure service ports – one for low pressure, and the other for high pressure. The gauge with the blue ring or accents is reserved for the low-pressure service port. Meanwhile, red is used for the high-pressure port. As your AC runs, you can measure the pressure. For low-pressure ports, this should read 25 to 45psi on the gauge. On the other hand, the high-pressure port should read 250 to 400psi.

What Should AC Pressure Be With Engine Off

If your AC pressure gauges are reading over 150psi with the engine turned off, it’s a sign that you might’ve overcharged your air conditioning system. Although to get a more accurate analysis, you should give it a few hours for pressure to equalize in the AC system. If it’s still reading 150psi, you’ll need to release pressure by evacuating some of the excess refrigerant/freon. However, you should note that 150psi may not necessarily be the threshold for all cars. Certain makes and models of vehicles may have varying limits for how high or low the AC pressure should be with the engine turned off. So, be sure to refer to your owner’s manual, as well.

How Much Freon Does A Car Hold

The majority of vehicles hold somewhere between 28 to 32 ounces of freon/refrigerant. That should equate to around 2 to 3 cans of freon, which typically come in 12oz capacities. Although, some stores sell freon/refrigerant cans in 6oz, 12oz, 19oz, or 22oz capacities. Moreover, you’ll also have to take into account the amount of leftover freon inside your car’s AC system at the moment. Thus, you won’t likely have to fill it entirely, anyway. There’s not really a good way to check how much freon is left inside your car (or if you’re overfilling it), other than using an AC pressure gauge to see if there’s too much or too little pressure.

How Much To Fix AC In Car

The cost to fix a car’s AC system varies significantly depending on the specific problem. Minor issues such as a refrigerant recharge might cost around $100 to $150. However, if the AC compressor needs to be replaced, it can cost between $500 to $1000 including parts and labor. Always get an estimate before any work is done to ensure you’re aware of the potential cost.

How Much Does It Cost To Fix AC In Car

Repair costs for car AC can range from as low as $100 for minor repairs or recharge, up to $1000 or more for more complicated repairs such as a compressor replacement. Other potential costs might include replacing the condenser, evaporator, or AC lines which typically cost between $200 to $800.

How To Use A/C Pro

A/C Pro is a refrigerant kit for DIY car AC recharge. First, start the car and set the AC to maximum cooling. Then, locate the car’s low-side AC service port and connect the A/C Pro canister’s recharge hose to it. After the gauge shows the current pressure, you can check the ambient temperature and compare it with the gauge reading. If the system is low, you can start adding refrigerant. Always follow the product instructions for safe and effective use.

How To Recharge AC In Car R134a

To recharge your car AC with R134a, first, locate the low-pressure port, remove the cap, and connect the recharge kit. Start the engine and turn on the AC to the coldest setting. Check the current pressure and compare it with the recommended pressure. If low, begin charging the system by pressing the trigger on the recharge kit. Stop charging periodically to check the pressure until it reaches the appropriate level.

Why Does My Car AC Only Get Cold When I Accelerating

If your car AC only gets cold when accelerating, it might be due to a low refrigerant level, a failing compressor, a damaged condenser, or issues with the AC’s electrical system. It’s recommended to have the AC system inspected by a professional to accurately diagnose and fix the issue.

How To Remove Excess Freon From Car AC

Removing excess Freon from a car AC should be done by a professional. They use a refrigerant recovery machine to safely remove and store the excess refrigerant. Doing this yourself can cause damage to the AC system and it’s also harmful to the environment if done improperly.

How To Bleed Off An Overcharged Car AC

To bleed off an overcharged car AC, you need a refrigerant reclaimer to safely remove excess refrigerant. If you don’t have one, it’s better to have this job done by professionals. Handling refrigerant improperly can lead to injury and damage to your AC system.

How To Check Freon Levels In Car

To check Freon levels, locate the low-pressure port of the AC system and connect an AC gauge. With the car running and the AC on full blast, check the pressure reading on the gauge. If it’s within the recommended range based on the ambient temperature, the Freon level is good. If it’s below, the system may need a recharge.

How To Use AC Gauges

AC gauges are used to check the high and low pressures of your car’s AC system. To use them, start the car and turn the AC on maximum. Attach the blue hose to the low-pressure port and the red hose to the high-pressure port. Once connected, you can read the pressures from the gauges. Make sure the readings align with the recommended pressures for your specific vehicle.

How Much Does A Car AC Diagnostic Cost

The cost of a car AC diagnostic can vary, but typically, it’s around $50 to $100. This cost can sometimes be waived if you proceed with the suggested repairs at the same facility. The diagnostic should uncover any problems with the AC system such as leaks, compressor issues, or electrical faults.

How To Fix Overcharged AC

To fix an overcharged AC, the excess refrigerant needs to be removed. This should be done using a refrigerant recovery machine, which most people don’t have at home. Therefore, it’s usually best to have this done by a professional. Overcharging can cause damage to the AC system, so it’s important to ensure the right amount of refrigerant is in the system.

How To Check Car AC Pressure Without Gauge

Checking car AC pressure accurately without a gauge can be challenging. However, you can roughly estimate by feeling the temperature of the air blowing from the vents. If it’s not cold enough, it may indicate low pressure. If the compressor keeps cycling on and off, it could indicate high pressure. For a precise diagnosis, it’s best to use a gauge or seek professional help.

Does The Car Need To Be Running When Adding Freon

Yes, the car should be running when adding Freon. This is because the AC compressor, which circulates the refrigerant, operates when the engine is running. Before adding Freon, turn on your car and set the AC to its maximum cooling setting.

What To Do If AC Pressure Is Too High

If the AC pressure is too high, it could indicate an overcharged system, a blockage, or a problem with the condenser. The safest and most effective solution is to seek professional help. They will properly diagnose the issue and take necessary action, such as removing excess refrigerant or repairing a damaged component.

Will A Bad Fan Clutch Cause AC Problems

Yes, a bad fan clutch can cause AC problems. The fan clutch is responsible for controlling the engine’s cooling fan. If it fails, it can lead to inadequate cooling of the AC condenser, causing the AC to perform poorly or not blow cold air at all. A professional should diagnose and repair this issue.

What Else Should I Know About AC Systems

Here, we’ll look at some other common questions about the air conditioning systems you find in cars.

Keep on reading to learn more about these fascinating systems.

History Of AC Systems

AC systems have been used in cars since the American company Packard first introduced them in 1939. However, they never really became popular with consumers due to things like the high cost and the large amount of space required.

Packard discontinued vehicles with AC units in 1941. The market remained AC-less until Chrysler brought them back onto the scene in the mid-1950s, offering them as an optional extra on the 1953 Chrysler Imperial.

This system had a switch on the dashboard with three different positions – low, medium, and high. As well as cooling the passenger cabin quickly, it also filtered out particulates such as pollen and dust and drew in more air from the outside than traditional systems. This meant that the car felt fresher on the inside.

After this year, CadillacBuick, and Oldsmobile also offered AC extras on a range of their vehicles. These AC units were provided by Frigidaire, a company that also produced units for Jaguar, Rolls Royce, and Bentley.

The real benchmark system – the one that, basically, we still use today – was developed by Nash. On the Nash Ambassador, the AC system was compact enough to fit under the hood alone, instead of across the hood and the trunk like most contemporary technologies. Perhaps most importantly, the company combined the AC and the heating systems to produce a basic version of today’s advanced climate control systems.

Why Does The Refrigerant Need To Be Cooled And Then Re-Heated

First of all, let’s briefly look at some important concepts you probably learned in high school physics and chemistry. Liquids are virtually impossible to compress.

You can test this theory for yourself by taking a syringe, half-filling it with water, and then putting your finger over the end. Is it possible to compress the water in the syringe? No. (Also, please don’t hurt yourself attempting this.)

Gases, however, are by comparison easy to compress.

This is due to the inherent molecular structures of liquids and gases.

The compressor must compress the refrigerant to keep the whole system flowing. In turn, this keeps everything cool.

If the compressor attempted to compress a liquid, it would simply break, for the reasons shown above. By the same principles, your pistons and con-rods can warp if coolant gets into the combustion chamber. The liquid can’t be compressed in the compression (or “squeeze”) stroke. Something has to give.

Secondly, as mentioned right at the start of this article, the AC’s main job is to remove heat from the air going into the cabin instead of just pushing cold air in. Where does that heat go? Into the system at the evaporator. From here, it goes back through the compressor and around to the condenser, where the environment cools it.

Does AC Waste Gas

As you’ll remember from the start of this article, the AC is driven by the fan belt, which loops around the crankshaft pulley and the AC compressor pulley. Because of this, it’s inevitable (because, physics) that the AC compressor pulley puts a drag on the crankshaft.

Since the crankshaft is the “power output” shaft of the engine, drag to it technically reduces the engine’s maximum power. By association, your fuel economy is also affected.

AC Low Side Pressure Too High

In old cars, the AC compressor could apply a lot of drag to the system. Yet, in newer cars, this effect is barely noticeable at all under normal conditions. The pulleys and the fan belt – not to mention the AC system overall – are all much more efficient these days.

The EPA released a statement concluding that driving with your windows down resulted in a more significant fuel economy decrease than driving with the AC switched on.

  • How hot it is outside, and how cold you want the incoming air to be. The greater the temperature differential, the more “work” the AC compressor needs to do.
  • Having the correct amount of oil for lubricating the system.
  • Make sure the system is correctly pressurized.

In 2015, the National Renewable Energy Laboratory estimated that the average modern AC system uses approximately 4 hp.


  1. Joven Ruthford

    I think Re-gassing or fixing an AC system requires specialized equipment and chemicals that you should need licenses to acquire. This is especially the case when it comes to the refrigerants used in your car’s AC.

  2. Tuan Phan

    Regasing. Ok s. Least spent money to bring back ac unit working again

    1. Harry Gibson
      Zack Norman

      Thanks for the comment, Tuan Phan!

      Glad to see that your car’s AC unit is working again. Usually, re-gassing fixes most AC-related issues, though it’s always a good idea to check the rest of the AC system for any leaks or component failure if a bit of Freon doesn’t solve things.

  3. Jeff

    My low side is very high. The high side is normal. What do you think the issue my be??

    1. Harry Gibson

      This could be a few things causing the issue if the low side is very high. I don’t like troubleshooting high pressure in a DIY method as you don’t want it going back. I would get your local air con guy to check it out incase you make things worse.


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