How to Check the Freon in a Home Air Conditioner in 4 Simple Steps

Josh Miller

Josh is a contributing writer to the site and former HVAC specialist.

Last Updated on November 24, 2021

Air conditioning units are innovative and ergonomic products that cool down a room and keep you and your family feeling refreshed during hot, stifling summer days and nights.

However, sometimes your conditioning system breaks down and stops functioning correctly. Most of the time, these operational issues are due to a problem with the unit’s internal electrical components, but they result from a freon leak on occasion.

If you suspect that your air conditioner is running low on refrigerant or coolant, you should follow four simple steps to calculate the unit’s superheating and subcooling values before contacting an engineer for help.

What is Freon and Why Does Your Air Conditioner Use It?

If you bought your air conditioner before 2003, it’s likely that this unit uses freon as its main refrigerant substance. Before looking at how to check the freon in a home air conditioner, it’s worth understanding more about freon and its uses.

Freon is a type of odorless, colorless gas that is a popular anthropogenic compound. In 1930, Pierre DuPont and his former company General Motors worked together to produce and trademark this distinctive compound under the brand name freon.

If your air conditioning system uses freon, it compresses and heats up this gas before pushing the hot vapor through a tangle of coils, where it becomes cool and turns into a liquid state. The liquid then passes through a specialist expansion valve, where it turns into a unique low-pressure gas that absorbs the hot air in the room and filters out colder air in its place.

Signs That Your Air Conditioner is Running Low on Freon

Most of the time, if your air conditioning unit isn’t working, it comes down to an electrical issue. However, sometimes your home air conditioning system will stop operating effectively because it’s running low on refrigerant.

Here are a few telltale signs that there’s a leak in your air conditioning unit and that the system is running out of freon.

You notice ice on the refrigerant lines

When your air conditioner is low on freon, this leads to lower head pressure levels throughout the machine. If your unit has low internal pressure levels, this causes a drop in the machine’s temperature levels, which results in the evaporator core freezing up.

This evaporator coil is the section where the unit’s refrigerant absorbs heat from the outside air, so when this part of the machine freezes, the liquid freon remains cold as it runs through the core. This leads to ice forming around the outside of your system’s refrigerant lines.

The refrigerant lines are emitting a buzzing or popping noise

If you’re worried about your air conditioner’s freon levels, put your ear to the unit’s refrigerant lines and see if you can hear a constant popping, fizzing noise. If you can, then this noise is most likely the sound of the liquid or gaseous freon leaking out of the insulated tubes.

The unit is blasting out hot or tepid air

If you notice that your conditioner is blowing out tepid, warm air rather than circulating cold, refreshing air, this could also signal that the system’s refrigerant levels are too low.

How Do You Check the Freon Levels in Your Home Air Conditioner?

If you strongly suspect that your machine is leaking freon, you should try calling an HVAC expert so they can repair the leak and add more refrigerant to the conditioner.

However, if you’re unsure about the cause of any issues with your air conditioner and you want to learn how to check the freon in a home air conditioner, then follow these steps to figure out the unit’s subcooling and superheating values. If the superheating value is too high, there’s not enough refrigerant in the unit’s evaporator section. If the subcooling value is too low, this is also a sign that there’s not enough refrigerant.

If it’s possible, check the unit’s pressure levels

Most home air conditioners will have pressure gauges built into the main unit’s side, so take a reading of the discharge and suction pressure levels. The discharge value is the pressure in the output section of your conditioner’s gas compressor unit, while the suction value is the pressure in the line moving into the gas compressor unit.

If you notice that the discharge pressure is too high and the suction pressure is too low, this indicates that there’s a problem with the system’s refrigerant levels.

Use a refrigerant slider tool to calculate the freon’s condensation and evaporation temperatures

Download a high-quality refrigerant slider tool online, and use this application to figure out the condensation and evaporation temperatures for your system’s freon.

Most of these apps are free and very simple to use. Start by figuring out the freon’s evaporation temperature. Use the drop-down menu to set the app to “freon refrigerant,” then turn on the dew function. Insert the suction pressure value you found earlier, and the slider tool will do the rest, giving you a corresponding temperature.

Next, turn on the bubble function, type in the discharge pressure value, and note the refrigerant’s condensation value.

Measure the temperature at critical points in your air conditioning system

You should now calculate the unit’s superheating and subcooling temperature values. To measure the subcooling temperature, hold a digital thermometer next to the discharge pipe that leads into the expansion valve section. For the superheating temperature value, hold this thermometer next to the suction pipe that flows into the gas compressor.

Figure out your superheating and subcooling ranges

Once you have these temperatures, you can figure out your system’s true subcooling and superheating values. To calculate the superheating value, take the refrigerant’s evaporation temperature away from the suction pipe’s temperature.

To calculate the subcooling figure, take the discharge pipe’s temperature away from the freon’s condensation temperature. If these final values lie somewhere around 5K for subcooling and 10K for superheating, then you can rest assured that your conditioning system contains the ideal amount of refrigerant. If either of these values varies drastically from these standard figures, you should contact an engineer so that they can come and sort out the issue.

Learn How to Check the Freon Levels in Your Home Air Conditioner

If you’re worried that there’s a refrigerant leak in your home air conditioner, you can follow four simple steps to calculate the system’s subcooling and superheating values. Once you know these values, you can tell whether your unit is running low on freon.

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