AC Low Side Pressure Too High: Possible Causes and Fixes

AC low side pressure too high is a common occurrence that many drivers face which can make driving uncomfortable, especially when driving in a hotter climate. A few people understand how it works as the AC system is a complex one, thus they don’t how to fix or prevent it.

AC Low Side Pressure Too High

Fortunately, we have done some digging and have discovered how the system works and what causes the low side of the AC to go high. We’ll also discuss how to fix the problem and how much it will cost you to do so.

What Is Meant by AC Low Side Pressure Too High?

AC low side pressure too high simply means that the AC system is failing to generate enough cool air to cool down the cabin temperature. This can be unbearable during the hot days as the temperature in the car gets hotter.

– Explaining the AC Low Side 

AC low-side is the part of the AC that has the evaporator and can be accessed by the port between the condenser and the evaporator. The port usually features a blue or black plastic cover that can be removed to access the low side.

Explaining the AC Low Side

On the low-pressure side, the refrigerant is transformed from liquid to air, which then absorbs the heat in the cabin. 

– Preventing the AC Low Side Too High

The best way to prevent the temperature of the AC Low Side from rising too high is to have a professional mechanic service the system instead of doing it yourself. This helps to eliminate all potential problems that could crop up later. 

Another way is to watch out for signs of leakage including hissing sounds from the AC low side. This enables you to detect a problem faster and solve it before it escalates.

– AC High Side Pressure Too High Low Side Low

If the AC’s high side pressure is too high and the low side is too low, it means that the AC has a problem and needs fixing. Some components of the system could be damaged or there could be leakage that needs to be stopped.

– AC Low Side Pressure Is Too Low

AC Low Side Pressure too low comes about when the air conditioning system is undercharged, which means there’s not enough refrigerant in the system. Another possibility is that the metering device could be blocked, thus the refrigerant is unable to move from the evaporator into the compressor.

When this happens, the AC fails to work well and the temperature in the car rises, making it uncomfortable on sunny days. The component causing the problem can either be fixed or replaced to enable the AC to do its job. Also, AC low side normal high side low is an indication that one or more of the components are broken

– Causes of AC High Side Too Low

Just like the other faults, this can be attributed to a broken component of the car’s AC system, particularly the condenser. However, if the condenser is working fine, then the AC pressure switch, the expansion valve, or the dryer could be at fault.

Causes of AC High Side Too Low

The task of the dryer is to remove all debris and moisture from the refrigerant. If it fails to do so, the moisture would cause low pressure on the high side and high pressure on the low side. If the metering device is blocked, then the refrigerant will not flow properly leading to higher pressure on the compressor. This will prevent the AC from cooling properly, leading to higher temperatures in the vehicle.

The AC pressure switch is a type of safety switch that is located inside the compressor and its duty is to regulate the flow of the refrigerant. The AC safety switch works in tandem with sensors on both the high and low sides to regulate the refrigerant. Thus, if there’s a fault on either side, the condenser would go off to protect the system. However, if the sensors fail and the switch doesn’t go off, there would be a false reading which could cause AC too low and the low side too high.

What Causes the AC Low Side Pressure To Go High?

The causes of the AC’s low side pressure going high is when there is a leak in any part of the system. If this happens, the refrigerant seeps out of the system and the pressure drops. Another possibility is when the system is filled with too much refrigerant.

– A Leak in the AC System

When there is a leaking problem in the AC system, the refrigerant, also known as Freon or the top essential part of the system, will seep out. When this happens the quantity of the Freon will reduce, subsequently lowering the pressure in the system. When the level of Freon drops, there won’t be enough refrigerant to absorb the hot air and cool the temperature in the cabin. Thus, the cabin will get hotter and more unbearable.

On the Low Side of the AC, it is common for the condenser and the evaporator coils to leak. Thus, they need to be replaced as fixing them is not possible. Replacing the evaporator can cost between $900 to $1200 while the condenser’s cost ranges between $600 and $800. Note that all prices quoted include parts and labor.

– Excess Refrigerant

Another cause of high readings on the low-pressure side of the AC is when the Freon level is too high, technically referred to as overcharged Freon. When the Freon is overcharged it mounts excess pressure on the condenser, which breaks down eventually. This is because the excess pressure from the overcharged Freon damages the valves and seals of the condenser. Excess Freon also causes the AC system to overheat and blow hot air instead of the expected cold one.

Excess Refrigerant

Note that AC low side pressure 150 PSI shows that the Freon is overcharged. To fix this, the excess Freon can be taken out by bleeding, which is done by a device that uses vacuums to draw out the refrigerant while monitoring the system to ensure the right volume of refrigerant is left in the system. This should cost you between $170 to $320.

However, the broken valves and seals of the condenser have to be replaced and we’ve already discussed the cost involved.

– Damaged Condenser Fan or Belt

A condenser fan’s job is to keep the condenser cool enough to convert the gas into liquid form before it goes to the evaporator. When the fan is damaged, the condenser can’t work properly and that would lead to a rise in the temperature of the AC low side. Thus, the air conditioner would malfunction and blow more heat into the cabin. The cost of replacing a condenser fan is between $260 and $370.

A condenser belt transfers power from the engine to the condenser to pressurize the refrigerant. Without a condenser belt, the AC system will fail to work and the car cabin’s temperature will rise. A damaged condenser belt can be replaced and it’ll cost between $80 and $210, including the cost of labor.

How Does the Air Conditioning System in a Car Work?

The air conditioning system in a car works when the compressor compresses the refrigerant, which becomes hot, and then flows to the condenser which cools it down. The refrigerator then turns into liquid which flows to the evaporator, becomes gas and is circulated in the car by the blower fan.

– Detailed Explanation

The main parts of the AC system are the refrigerant, also known as Freon, the compressor, the condenser, the evaporator, the expansion valve also known as a metering device, and the electronic control unit.

When the driver starts the AC system, the engine’s belt drive powers the compressor to compress the refrigerant – an action that drives the refrigerant’s temperature high. The hot refrigerant now flows to the condenser; a set of coils that cool the refrigerant and turns it into liquid. The liquid refrigerant goes through the evaporator which transforms it into cool air.

Before the cool air enters the car cabin, it passes through the expansion valve which expands and regulates the cool air to maintain proper pressure. The cool air is then circulated in the cabin by the blower fan. The cycle is repeated when the expanded refrigerant (cool air) reenters the condenser. The electronic control unit helps to regulate the various aspects of the AC unit so that a comfortable temperature is maintained in the vehicle.

– Checking the Pressure of the AC

Ideally, checking the pressure of the ac should be done by a professional to get the right results. However, you can also do it but ensure that you use the tools properly and read the results accurately. First, you’ll need an AC pressure gauge which costs between $35 and $55. Attach the pressure gauge to the Compressor’s low side and then turn on the engine.

Checking the Pressure of the AC

After turning on the engine, turn on the AC and increase it to the highest level. Check the pressure gauge and write down the value on it. Now compare the value you just recorded to the pressure rating for the AC low side recommended by the manufacturer in the car manual. If the reading from the pressure gauge is higher than the recommended values in the manual, then the air conditioning system is broken.

– Detecting if the Car AC Is Leaking

Now that we know that a refrigerant leak causes high temperatures on the low side of the AC, let’s find out how to detect them. The easiest way is to listen for a hissing sound coming from the air conditioning system. The hissing sound could be the refrigerant escaping holes or cracks on the many tubes that connect parts of the system. Thus, you have to listen attentively as some hissing sounds can be barely audible.

A second way to find out whether the AC is leaking is to examine the tubes to find out if there’s any leakage. Look for signs of moisture around the tubes and other components of the system. If you find one, then there’s a high chance that the refrigerant is leaking. The best way to fix any of these problems is to have the damaged part replaced.

– Replacing the Compressor if It’s Leaking

Replacing the AC compressor should be done by a professional mechanic, however, if you want to do it on your own, here is one way to go about it. The first step is to find the compressor which is situated under the car’s hood near the front passenger side. Once you find it, make sure you remove the negative battery terminal cable to avoid electrical shock while replacing the compressor.

The next step is to remove the two wires connected to the back of the compressor, then unscrew any fasteners anchoring the compressor and then take out the compressor from its mount. Replace the old compressor with the new one and secure it with bolts and nuts.

Connect the two cables you removed from the old compressor to the new one and connect the negative terminal cable of the battery to the compressor. Start the car’s engine and turn on the AC to check whether it is now functioning properly or not.

Frequently Asked Question

1. What Is the Recommended Value for Your AC Low Side Pressure?

The recommended value for your AC low-side pressure must be closer to 30 psi at a temperature of 90 degrees Fahrenheit. Any value that is too low or too high outside the given pressure range is an indication that the AC has developed a fault.

The value for AC low side pressure for the R134a refrigerant is between 22 and 57 psi.


So far, we’ve discussed the various reasons why the pressure of the AC low side would go high and how to fix the problem.

Here’s a recap of all that we’ve discovered:

  • AC low pressure too high is the phenomenon where the AC system fails to generate enough cool air to circulate in the car.
  • The various causes of this phenomenon could be a leak in the AC system, a damaged condenser belt, and an overcharged AC system.
  • The best method to fix the problem is to replace whichever component of the AC system is causing the problem.

To prevent an R410a low side pressure too high, have a professional service the AC system and repair or replace the necessary components. Also, watch out for signs of leakage or hissing sounds coming from the AC system so you can detect the problem early and have it fixed.

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