Is Your Central AC Low on Freon? When to Recharge It

How do you know if your central AC needs to be recharged?

I want to start by saying that not all air conditioners use Freon. In fact, newer air conditioners use Puron (R-410A) and other refrigerants but not Freon (R-22).

Most people use the term Freon to refer to any refrigerant that is used in air conditioning. I have therefore purposely used the words Freon and refrigerant interchangeably throughout this post.


The last air conditioners that use Freon were manufactured in 2010. Production and importation of Freon in the United States was stopped in 2020 in line with the requirements of the Montreal Protocol.

The production and use of Freon as a refrigerant was stopped because it was discovered that Freon depletes the ozone layer resulting in global warming. As a matter of fact, Freon’s global warming potential is about 2000 that of carbon dioxide.

It is however not illegal to use Freon or have Freon-using air conditioners. Freon (R-22) is however currently very expensive due to dwindling supplies. recycled Freon is also available but expensive as well.

A refrigerant is used to remove heat from indoors and release it to the outdoors through the AC’s outside unit. It does so by changing state from liquid to gas and then back to liquid again?

Your central air conditioner has a close-looped system. That means that you actually don’t need to regularly top it up with Freon. If you suspect that your AC is low on refrigerant, it is a sign that the system is leaking somewhere.

So, how do you know that your central air conditioner is low on Freon or any other refrigerant and that it needs to be recharged?

The signs that your AC is low on Freon/refrigerant and that it needs to be recharged are:

  • AC is running but not cooling the house
  • There is ice buildup in refrigerant line
  • The energy bills are unusually high
  • Hissing/bubbling sounds when the AC isn’t running
  • The air from the vents is warm

Unfortunately, the smell of Freon is not as strong as that of natural gas. If your air conditioner is leaking, you are therefore not likely to notice it.

Why Your Air Conditioner is Low on Freon


An air conditioning system is made up of 3 components. These are the compressor, condenser coil and evaporator coil.

The 3 components are connected together using copper pipes. Freon/refrigerant is then cycled between these components where it easily changes state from gas to liquid and back to gas again and in the process remove heat from indoors thanks to its high latent heat of vaporization.

Unlike the gas used in your car, an air conditioner’s refrigerant should never get depleted. It only changes from one state to another but it is never used up. Air conditioners use electrical energy to run but not Freon.

Therefore, as I had earlier mentioned, if you think that your central air conditioner (or any other air conditioner for that matter) is low on Freon, you need to call in an HVAC technician as it is a sign that the refrigerant is leaking out.

The thing about air conditioning is that it is really hard to diagnose a problem unless you are a trained technician. You could be thinking that your AC is low in Freon while in essence you could be dealing with a bad compressor or fan.

How Do I know if My Central Air is Low on Freon?

Just to remind you, Freon in this case refers to the actual Freon (R-22) or any other refrigerant used in air conditioning. Many folks haven’t yet get used to Puron or the various other newer refrigerant brands.

In more details now, the following are the telltale signs that your central air conditioner is low on Freon:

1. AC is Running but not Cooling the House

As I mentioned earlier, the work of the refrigerant is to cool the house by absorbing heat from the indoor air. When Freon enters the evaporator coil inside the house, it is usually in the form of a cold liquid.

The cold refrigerant liquid absorbs heat from the warm indoor air until it (Freon) evaporates and enters the compressor as a gas. As it evaporates, its takes with it heat from house.

Now, if there is no sufficient refrigerant in the air conditioning lines, heat from the indoor air will not be absorbed. As a result, you will notice that the AC is running but the air inside the house is still warm.

2. High Electricity Bill

Your house is equipped with a thermostat whose function is to send a signal to the various AC components to start running as a soon as the indoor temperature drops below its (thermostat) settings.

If the air conditioner is unable to cool the air inside the house as per the thermostat settings, the thermostat will signal the AC to keep running in a bid to try and cool the house.

Needless to say, the longer your AC runs the more the power it consumes and the higher your utilities bill.

3. Ice Buildup on Refrigerant Line

Where you central air conditioning system is low on Freon/refrigerant, the evaporator coil inside the house gets too cold, resulting in a backflow of the Freon (now a cold liquid) in the refrigerant line.

Due to the difference in temperature between the refrigerant inside the line and the surrounding air, condensation takes place and ice starts to build up on the refrigerant line.

It is the same thing that happens when you are inside your car (warm) while it is freezing outside. Your car windows will after sometime become foggy and you will need to turn on heat to defrost them.

I should mention that ice buildup on an AC’s refrigerant lines is a serious problem. If not fixed in good time, the liquid can flow back all the way back to the compressor.

A compressor should only compress the refrigerant in its gas state. A liquid inside the compressor will without a doubt damage it resulting in even more expensive repairs.

4. Hissing or Bubbling Sound

It is not easy to notice a leak of your air conditioner’s refrigerant but if it is a major leak you sure can. A hissing or bubbling sound from the refrigerant line or even coil is a good sign that Freon is leaking from your AC system.

Can you detect if your AC’s Freon is leaking by the sense of smell?

At low concentration, a Freon leak will have no distinctive taste or smell. However, if there is a lot of the Freon leaking (high concentration), the Freon will have a slightly sweet smell. The smell can also be similar to that of nail polish, paint or paint thinner.

5. Heat Pump not Heating the House

A heat pump is basically an HVAC system that works pretty much like a central air conditioner during the months of summer but also heats the house during winter. From the outside, heat pumps and central air ACs look exactly the same.

A heat pump has a reversing valve that allows high-pressure superheated refrigerant gas to flow to the evaporator instead of the condenser coil. Inside the house, the cold indoor air absorbs heat from the refrigerant and that is how the house is heated.

If the heat pump system is low on Freon, it will be unable to extract heat from the surrounding air meaning that the heat pump will not have energy to heat the house.

Because heat pumps are always equipped with a secondary source of heat, you will therefore notice that the auxiliary heating will always be on in your thermostat even when it shouldn’t be.

How Do You Know Which Refrigerant You AC Uses?

To check the type of refrigerant used by your air conditioner, look for a nameplate or label on the air conditioner’s outside unit, also known as a condenser unit.

On the nameplate you will find more details about the air conditioner but importantly you will see the type of refrigerant it uses. You can also find that information on the unit’s user manual if you still have it.


And basically those are the major signs that your central AC system is low on Freon and that it needs to be recharged.

Unfortunately, this is not something you can do on your own. A licensed HVAC technician will first need to find and fix the leak before recharging the system.