How To Check AC Refrigerant Levels (Freon Levels)? [ 4 Methods Included]

We are accustomed to living in an air-conditioned house on hot days. However, just like any other electrical appliance, air conditioners can malfunction at some point, and a low refrigerant level is frequently to blame. Because Freon is the most well-known refrigerant brand, many people refer to it as Freon level.

So, how do you check the refrigerant level in your air conditioner? In this post, I’ve summarized four methods: a sound test, a soap test, a sniffer, and calculating subcooling and superheating.

If you are not an HVAC specialist, you may have never heard about these methods before. Don’t worry, in this post I’ll walk you through each method and provide you with more important information about checking AC refrigerant levels.

Let’s get started!

Effects of low refrigerant level on AC

Due to the Freon ban, most air conditioners made after 2010 use another refrigerant – R-410A, rather than R-22. R-22, also known as Freon, can cause the ozone layer’s depletion. 

However, regardless of the type of refrigerant used in your air conditioner, they all operate on the same principle. By converting from liquid to gas, the refrigerant can absorb a large amount of heat and thus cool the evaporator coil.

When warm air passes over the cold evaporator coil, the air temperature drops below the dew point, causing cold air to return to the house.

In most cases, the refrigerant will remain untouched in the coils. However, when there is a Freon leak caused by metal corrosion, tear and wear, or other factors, the level can drop.

Many people wonder if running an air conditioner with low Freon is harmful. They may want to leave it unattended if it is safe.

Unfortunately, it is not a good idea. Low refrigerant levels can lead to decreased energy efficiency and performance. Furthermore, the refrigerant that leaks into the air will cause respiratory problems for you as well as environmental damage.

As a result, you should hire a certified HVAC technician to repair the refrigerant leak and recharge it.

Signs of low AC refrigerant levels

Before contacting a pro, some common signs indicate the refrigerant level in your AC may be running low. You can make the correct decision by combining these signs with the refrigerant level checking methods.

1. An increase in the utility bill

When the refrigerant level is low, the air does not cool as efficiently as before. To achieve the desired room temperature, your air conditioner will have to work harder, causing overloading in your machine and a noticeable impact on your electricity bill.

2. Blow warm air

Because of the low refrigerant level, your air conditioner will be unable to lower the air temperature as effectively as before, or it will take significantly longer to cool your room.

Place your hand near the vent. If you notice the machine blowing hot air. Your air conditioner most likely has a low refrigerant level.

3. Frozen evaporator coil

There are numerous causes of frost or ice on the coil, one of which is a low Freon level. With the same powerful fan and compressor, the temperature in the evaporator coil will drop significantly.

Rule out the issues of fan and filter on AC

While low AC refrigerant levels may be the primary cause, other factors can also contribute to AC malfunctions. As a result, you can rule out these possibilities before checking refrigerant levels.

Clogged air filter

It is recommended that the air filter be cleaned on a regular basis. A clogged filter will reduce airflow and cause the evaporator to freeze, affecting the performance of your air conditioner. You can open the exterior and inspect the air filter.

If it is clogged with lint and dust, clean it and check to see if your AC is working again.

Failed fan

A fan is used in air conditioning systems to draw air into the machine. If it fails, your air conditioner will be unable to keep your room cool.

Examine the fan when the air conditioner is turned on. It could be the root cause of your faulty air conditioner if it can’t rotate as quickly as usual.

Checking AC Refrigerant levels – 4 Methods

If you want to go one step further and confirm the problem, you can use the four methods listed below to check the Freon level in your air conditioner.

Because low AC refrigerant levels are caused by freon leaks, most methods check the Freon level by detecting leaks.

1. Sound test

The leaking hole on the lines and coils can grow in size over time. When the leak becomes significant, it will make a hissing or bubbling sound. To determine where Freon leaks out, listen to all points along the line.

2. Soap test

Because the motor is noisy, you may not be able to hear the sound. If this is the case, you can apply soapy water to the area where you suspect the leak will occur.

When refrigerant runs out, it will produce bubbles when it comes into contact with soapy water. Similarly, it will only occur if the leak is substantial.

3. Use an electronic leak detector

check freon level in ac

Several types of Freon sniffers are now available on the market as a result of technological advancements.

When the sensor in the detector detects Freon or another type of refrigerant is in the air near the AC, a sound is produced.

Many detectors, however, are not as accurate and reliable as they appear to be.

4. Calculate subcooling and superheating

This method is more complicated, but it is also more accurate. At a certain temperature and pressure, refrigerant can evaporate or condensate.

To ensure that the refrigerant successfully converts from one form to the other, set the temperature slightly higher for evaporation and slightly lower for condensation.

The temperature difference is referred to as subcooling and superheating. Subcooling should be around 5 degrees Kelvin, and superheating should be around 10 degrees Kelvin. When subcooling is too little and superheating is too much, it often represents low refrigerant level.

The temperature of evaporation and condensation will vary depending on the type of refrigerant and the local air pressure. You can get the correct numbers by using this widget.

The temperature on the suction and discharge pipes should then be measured with a thermometer.

Finally, you must use the equation below to calculate the subcooling and superheating.

Superheating = temperature of suction pipe – evaporation temperature
Subcooling = condensation temperature – temperature of the discharge pipe

If the subcooling is less than 5 Kelvin and superheating is over 10 Kelvin, you can confirm that the refrigerant level in your AC is low.


This guide demonstrated how to check the refrigerant level in an air conditioner. Some signs can assist you in making an initial judgment, but the four methods mentioned in the previous section will be more accurate.

If you discover that your air conditioner is low on Freon or other refrigerants, do not attempt to refill it yourself. Hiring a certified professional is the best option.

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Liz Yang is the founder of Airsmartly. She has been working at home for a few years and realizes that the performance of the HVAC system plays such an important role in our life. She has tested a lot of products in person, like humidifiers, air purifiers, dehumidifiers, and ACs, and wants to share tips about using or troubleshooting these products with you. Her uncle is an HVAC expert with over 30 years of experience in the field, and often offers assistance when she is unsure how to handle a situation. He is also in charge of reviewing the articles on this site.

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