Measuring superheat and subcooling in air conditioning is critical to a troubleshooting process. To help you refresh your HVAC skills, this article will give a comprehensive insight into the dynamics of both terms. We will explain the meaning of each, how to measure it, who can measure it, mistakes to avoid, and outline tools you can use to measure superheat and subcooling. Read on to learn more.

What is Superheat?

To understand the meaning of superheat, which is a complicated term for newbie technicians, it is important to understand saturation. Saturation is a term that describes the temperature at which a substance changes its form. It’s the level to which liquid must heat to convert to vapor and gas to become liquid. In the former case, saturation is used interchangeably with boiling point and condensing point in the latter.

Following the above, superheat is the difference between the temperature of the refrigerant vapor and its saturation temperature.

What is Subcooling?

When condensation occurs, it signifies that vapor has lost its previous heat and now turns into a liquid. Subcooling is the drop in the temperature at which vapor becomes a liquid.

Why You Need to Know How to Measure Superheat and Subcooling

Understanding the measurement of superheating and subcooling is essential for a technician. It helps to discover the cause of the system’s problem and implement a proper line of action.


In addition to this, measuring superheat and subcooling saves the technician from costly errors. While measurement is just one of many approaches to repair, it is still essential to an expert’s assessment.

Measuring Superheat and Subcooling in Air Conditioning: How to Do It

Measuring superheat and subcooling in air conditioning can make repairs a lot easier. The process makes it easy to itemize problems that need fixing in an AC system. The following are steps to take for measuring each.

Measuring Superheat

Start the refrigeration system and allow it to run for about 10 to 15 minutes. This will help to create steady temperatures. Locate the suction service valve between the evaporator and the compressor and connect it to the refrigerant manifold gauges. Afterward, join the pipe clamp thermocouple to the suction line you find close to the suction service valve.

Link the thermocouple to a digital thermometer. When you have done this, determine the suction line pressure with the refrigerant pressure gauge. Note this pressure and the temperature of the suction line from the thermometer. Now, using the refrigerant temperature chart, convert the pressure gauge reading to evaporator saturation temperature.

After this, deduct the saturation temperature from the thermocouple temperature. The result here is the superheat for the AC. You should check your system’s specifications to know its superheat. When the superheat is insufficient, it can cause refrigerant to return to the compressor in its liquid form, creating damage. On the flip side, when excessive, it can cause the compressor to overheat and impact system capacity.

Wrong superheat can also signal issues such as a dirty condenser coil, clogged filter, or a problematic thermal expansion device.


Measuring Subcooling

To create steady-state temperatures, run the refrigeration system for ten to fifteen minutes. Next, join the refrigerant manifold gauges to the discharge service valve. Follow this by joining the pipe clamp thermocouple to the refrigerant line you will find between the condenser’s discharge and the thermal expansion valve.

Next, measure the pressure of the condenser at the service valve by checking the pressure on the refrigerant manifold gauges. Check the digital thermometer for the thermocouple temperature. Now, convert the temperature reading to condenser saturation temperature using the refrigerant temperature chart.

When you deduct the condenser saturation temperature from the thermocouple temperature, you find your subcooling. Like superheating, insufficient subcooling can result from a problematic thermal expansion valve, low refrigerant charge, and an inadequate flow of air over the condenser.

Common Mistakes in Measuring Superheat and Subcooling in Air Conditioning

As someone new to the HVAC world, it is normal to face issues at the opening stage. We have listed some common mistakes below to help you avoid them:

  • Measuring the pressure at the compressor instead of the evaporator: When you do this, you get a false superheat value which is often higher. This can cause you to wrongly adjust the TXV system to accommodate the figures. You could also make the mistake of relying on tools that are not correctly calibrated and inaccurate. Recording the superheat when the system is not yet at a steady state. Lack of knowledge of the correct values. Not following the right steps and moving too fast.

Who Can Measure Superheat and Subcooling in Air Conditioning?

Measuring superheat and subcooling in air conditioning is a task that can go wrong without proper skill and care. Among technicians, it requires both experience and conformity to tested standards. If you do not have the right qualifications, it is best to entrust measurement to experts.

An issue you might encounter when you do it yourself is a misdiagnosis of the problem. On the surface, the issue can appear related to the refrigerant. Therefore, applying what would have been the right solution can yield the wrong results. To avoid this, you should call a service expert to do the job.

In addition, there may be legal restrictions in your state on who can fix certain HVAC problems. You should look out for this to prevent complications. A technical result of checking the superheat and subcooling of your AC is overcharging or undercharging the system. This imbalance can cause serious issues.

Summarily, leaving superheating and subcooling maintenance to an expert is a better line of action.

Tools for Measuring Superheating and Subcooling in Air Conditioning

To get an accurate measurement of superheat/subcooling in an AC system, you need a set of tools. First among these is the superheat/subcool gauge. Prices for this can range between less than a hundred dollars to three hundred.

You might want to purchase a gauge that suits most refrigerants. Examples are the R134a, R22, R410a, and the R404a. They will remove the need to enter the specs of the refrigerant you are working on within the field.

Another tool you might want to have is a software tool for converting pressures. A variety of them exist for troubleshooting HVAC, and you can even find some that are free to use. They come in Android and iOS versions, possess qualities that adapt to whatever you’re working on, and offer a dynamic range of features.


How to Prevent Problems With Your Air Conditioning

Superheat and subcooling measurements become necessary when there are problems in the system. To avoid these technical processes that cost you, you can follow the tips below.

Condenser Coil

The condenser coil is responsible for transferring interior heat to the outer part of your building. It begins to malfunction when it is covered in dirt and other materials that affect efficiency. Your system works harder but produces lesser results.

To avoid this, create a special cleaning routine for your unit. The more sanitary attention the unit gets, the lower the chance of problems.

Evaporator Coil

This coil is an integral part of the system. It is filled with refrigerant but also needs heat to function properly. When there is an issue with the airflow, your coil freezes and produces less air or none at all to the interior.

Issues with coils are often linked to dirty air filters. As such, regular cleaning and replacement are crucial to avoiding problems.


Depending on the air conditioning type you use, your system conveys air through a network of ducts. If leaks occur along these lines, the AC’s output wastes within the walls, meaning the unit has to work harder to compensate.

To prevent this scenario, you can schedule regular maintenance checks with an HVAC expert. This will help to detect and fix problems earlier.


You will commonly find a pair of fans in your air conditioning system. One blows air over your evaporator coil for cooling purposes and the other, which is outdoors, expels the heat. Either of these can malfunction due to worn belts or insufficient lubrication. When that happens, neglecting the issue can result in compressor failure, which damages your AC.


The refrigerant helps to remove heat from within your home. In certain cases, it becomes insufficient due to leaks in the refrigerant lines. Responding to this is not merely a matter of adding more refrigerant but tracing those leaks for repair purposes. This consumes time, is expensive, and will need an expert.

It is best to run periodic checks to find leaks early and save costs.


The drains collect the moisture your air conditioning has utilized. Overfilled or clogged drains not only affect the system but can damage your home as well. The best way to handle it is by conducting checks to clear them up.

Reach Out to Us Erica's Plumbing, Air Conditioning & Restoration in Boca Raton FL

In this article, we have detailed the steps in measuring superheat and subcooling in air conditioning. However, it is important to mention that this alone is inadequate. To get an accurate measurement and avoid errors, you need the right set of tools. You may also want to work alongside an experienced technician to observe things practically.

If you are a homeowner in Florida and you need an expert to troubleshoot your system, contact us at Erica's Plumbing, Air Conditioning & Restoration. We are a time-tested company based in Florida. We are also available 24/7. Schedule an evaluation now.

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