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Is Your AC Low Side Pressure Too High? Here’s The Reason Why

Ac Low Side Pressure Too High

It’s the height of the summer season and you’re all prepped up for a long drive across the country for that much-needed summer vacation. But, there’s just one problem. Your AC is not working properly. No matter what you do, your car still feels like an oven.

If this is the case, then there might be an issue with the compressor, or the refrigerant may be leaking out. The good thing is, there’s a way to find out the problem and diagnose whether your AC system is still healthy. You just need to check the pressure readings.

But, what if the readings say that the AC pressure is too high, especially the low side pressure? Read on to find out what causes these readings, and what you can do about it so your car’s AC system goes back to normal in no time.

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Why are AC readings important?

First of all, why are AC readings important, and what does it tell you?

Well, the pressure readings of your AC system is what indicates whether the AC is functioning properly, or if there are underlying problems, such as leaking refrigerant, system damage, or worse, compressor failure, which can easily cost you a fortune in repairs.

Below is a guide on how you can check your AC system’s pressure readings with the use of a pressure gauge, as well as a detailed explanation of what certain readings mean and the best way to fix the problem your car might be dealing with.

Check the AC pressure with a pressure gauge

Checking AC Low Side PressureIf you want to easily check the pressure readings of your AC system, a simple way to do it is by using a pressure gauge, which you can buy for a cheap price at your local shop or from online stores like Amazon.

Just follow the user instructions of the pressure gauge to read your AC’s high side and low side pressure. The correct pressure readings depend on what car you have, and you can find the correct numbers out from your car manual.

Here’s a simple guide that you can use to compare your readings with:

When the engine is off

When the engine is off, the readings shouldn’t be close to 0 or over 150 psi. Low readings mean that there is almost no refrigerant, which may be caused by leakage, while high readings suggest that the system is overcharged.

If either of these scenarios is the case, you need to either check for leaks and have any issues repaired before filling up the system with refrigerant to the correct specifications, or have a mechanic safely release pressure off of the AC system.

When the engine is on

When the engine is on and the AC is on high, low pressure readings should be around 30 psi and the high pressure side should be about 250 psi depending on your car. The correct reading will display once the clutch engages and the gauge stops cycling.

If there are readings on both the high and low sides but they are not the correct specified pressures, it means that certain parts of the AC system are not functioning properly, such as the expansion valve, compressor, and clutch.

AC pressure readings and what they mean

I have talked a bit on what the correct AC pressure readings should be, and what are the common issues that you might be encountering if the readings are wrong. Now, we’ll go into depth about each of these issues so you’ll have an idea how to address them properly.

High pressure when the engine is off

When there is higher than normal air pressure if the engine isn’t running, this means that there is high pressure in the condenser fan, which is what cools the AC system by passing air through it. This high pressure is commonly caused by two problems:

Pressurized condenser fan

First, there might be debris blocking the flow of air from the condenser fan motor, or the motor itself is damaged, leading to little to no airflow through the condenser. This means that the condenser fan cannot efficiently and quickly cool the AC system.

A highly pressurized condenser fan results in distortion of the aluminum in the compressor, as well as leakage from the evaporator coils. When these things happen, repair costs can easily reach a thousand dollars.

Overcharged AC system

The other usual cause of high pressure readings is that the entire AC system may be overcharged, which happens either when there is too much refrigerant or too much oil. In this case, pressure must be released by a certified mechanic.

However, it’s not always that the system is actually overcharged. You might get a false high reading if the engine is running or if air enters the system. Nonetheless, to avoid overcharging your system, make sure to first check whether there are any leaks along the lines, hoses, and compressor.

High side pressure is too high (low side pressure is low)

Now, when the engine is on and running, and the pressure gauge still reads a high pressure on the high side while the low side pressure keeps dropping, it should be clear that the underlying issue has to do with the condenser.

More specifically, there is restricted air flow in the condenser due to blockage. As such, this blockage and debris should be removed. To avoid this problem in the future, you can regularly inspect the health of your condenser by using a DIY condenser fan speed test kit.

Low side pressure is too high (high side pressure is normal)

Finally, if you’re wondering why your AC pressure reads too high on the low pressure side, while the high side pressure remains normal, you might be dealing with incorrect cycling of the condenser.

This happens when there is an unusually rapid cutting in and out of the cycle. It’s not a common occurrence, and requires a professional to resolve the issue. You’re also likely to be dealing with a thermostat switch malfunction due to a wrong temperature gauge, and in such case, the thermostat switch needs to be replaced by a mechanic.

Other common AC system issues

Repairing AC Low Side Pressure Too High

Aside from the ones I’ve already mentioned above, there are a few other problems that might be going on with your malfunctioning AC system. These include using an inappropriate compressor lubricant, having a low or old oil system, or issues with loose wirings and slipping belts.

Most of these issues and more can be exposed when you rigorously test your AC system’s pressure readings, and you have a clear understanding of what each reading means. But, for a closer inspection and a more accurate diagnosis, it’s still best to take your car to the local mechanic.

A few reminders before you go:

  • When testing your car’s AC system pressure, make sure to proceed carefully, follow instructions properly, and use your car manual as a guide on what you should expect the readings to be for your vehicle.
  • One of the most common issues you may have when it comes to your AC system is leakage. Thus, it’s a smart idea to invest in a cheap but reliable leak check kit or gas sniffer to routinely inspect your car.
  • Another common problem with car ACs arises from adding way too much refrigerant, which affects the condenser and other components of the AC system, resulting in low AC temperature and significantly worse issues.


It’s quite easy to diagnose the health of your AC system and any underlying problem it may be facing, as long as you have the right tools and you know what you’re doing.

However, know your limits as to what sorts of inspections, maintenance, repair, and replacement works you can safely and successfully undertake on your own. It’s easy to make a simple problem worse with a single mistake that will cost you big bucks later on.

Furthermore, trust your local mechanic when he says certain things need to be fixed, and address the issue as soon as possible even if it costs a sizable amount of money. Ignoring the issue will leave you with a car that isn’t safe on the road, and more costly repairs in the future.

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