Refrigerant leaks are one of the most common problems with older air conditioners. Once the coil springs a leak, you are often better replacing the air conditioner, although your HVAC contractor may recommend repairs if the unit still happens to be under warranty, or if the crack in the coil is very small. How can you tell whether your AC unit has a refrigerant leak? Look for the following signs:

Colored liquid beneath the air conditioner

Clear fluid beneath the air conditioner does not indicate a refrigerant leak, although it may indicate that your condensate drain is clogged. (This is a minor problem — you can generally unblock the drain simply by cleaning it.) However, if you see a green or pink liquid beneath the unit, that's refrigerant. The pink liquid is a newer refrigerant called R-401a. The green liquid is an older refrigerant called R-22. If your AC unit was installed before 2010, it probably has R-22, in which case it will definitely need to be replaced because R-22 has been phased out.

Constant freezing over

If your air conditioner freezes over, it could simply be due to a dirty air filter. However, if you clean the air filter and ice keeps building up on the condensing coil, you probably have a refrigerant leak. When there is not enough refrigerant left in the coil, it expands too much, which means it cools too much — so much that the coil freezes. 

Hissing sounds

If you venture outside when the air conditioner is running, you may hear some hissing or whistling sounds coming from the coil. This is the sound of the coolant escaping from the cracks in the coils. It hisses because it is still in the gas state inside the coil and is moving very quickly through the cracks.

Loss of cooling power

Usually, an air conditioner that is leaking refrigerant will continue to cool somewhat, but it will not do so as effectively. You might notice that your home does not cool to below 78 degrees on really hot days, or that some rooms stay warm while others are cool. This symptom will continue to worsen if you keep using the air conditioner, as more and more refrigerant will leak out.

If you suspect your AC unit has a leak, contact your local air conditioning repair services. They can come and investigate, and if there is indeed a leak, they can give you quotes for repair and replacement options.