Discovering that your air conditioner is frozen with ice can be perplexing. Air conditioners are designed to create cool air but not to the point of freezing. It takes a temperature of 32 degrees Fahrenheit or below for water to freeze, which is far beyond the cooling capabilities of most residential air conditioning systems.

Freezing, however, is a somewhat common phenomenon with air conditioners. It usually occurs with the evaporator coil or a refrigerant line. If you notice ice on either of these components, you might be wondering what’s causing it.

Refrigerant Leak

One of the most common reasons air conditioners freeze up is because they have a refrigerant leak. Refrigerant is the substance – it cycles between a gas and liquid state – that collects heat from the air inside your home. It’s designed to operate in a closed and sealed system. Refrigerant will collect heat at the evaporator coil, and it will release this heat at the condenser coil.

If the system is breached, refrigerant will leak out. Depending on how much refrigerant leaks out, it may cause your air conditioner to freeze up. With low refrigerant levels, it won’t collect as much heat from the air inside your home. Therefore, the excessively cold refrigerant may freeze the evaporator coil or refrigerant lines through which it flows.

Obstructed Vents

Your air conditioner may freeze up if the air vents are obstructed. Vents allow air to circulate throughout your home. At the same time, they move the warm air to the evaporator coil where the refrigerant can absorb the heat. If your vents are obstructed, the evaporator coil may receive an insufficient amount of warm air, which can cause it to freeze.

Make sure both your return and supply vents are unobstructed. Return vents draw air, whereas supply vents release conditioned air. You can typically close a few supply vents without any ill effect, but you should keep all of your return vents open.

Clogged Air Filter

A clogged air filter can cause your air conditioner to freeze up as well. Before reaching the evaporator coil, air must travel through the filter. A clogged filter will restrict the amount of air that passes through it. With less air reaching the evaporator coil, your air conditioner may freeze up.

If your air filter is clogged, you’ll need to replace it. A clogged air filter will lead to a higher level of indoor air pollution while also increasing the risk of frozen air conditioning equipment.