Why Does My AC Freeze?

Cooling Process

• Air conditioners cool by both cooling air and removing humidity. Inside an air conditioner are a set of coils that are either cooled by a gas, such as Freon, or by chilled water. As hot air passes over these coils, the air is cooled and humidity condenses. Cooled air is blown out of the air conditioner and heat is vented to the outside. The condensation collects in a pan or is piped into a drain. Some window air conditioning units have a drain that allows the condensation to drip outside.

Causes of Freezing

• Since air conditioners require air flow to function, an air conditioner will freeze if air flow is obstructed. The most common cause of air conditioners freezing is blocked or dirty filters. If the condensation does not drain properly, an air conditioner can freeze since water blocks where air needs to pass. Some air conditioners are not designed to be run when the outside temperature falls below 65 F and will freeze when this occurs. In air conditioners that use a gas such as Freon to cool, low coolant or a leak in the pipes containing the coolant could cause the unit to freeze.

Solutions

• If an air conditioner has frozen, turn off the air conditioner and allow it to thaw. Running the air conditioner on only the fan setting will thaw the ice quicker, as will aiming a hair-dryer at the ice. Do not attempt to dislodge the ice by poking at it, as this can damage the delicate insides of an air conditioner. If the air conditioner has a hole to drain condensation, check to make sure that it is clear and that water can drain from it. If the air conditioner is clean and draining properly but still freezes on a hot day, then the cause could be a Freon leak. Freon leak repair requires specialized equipment and training, so consult a qualified repair person if this is the cause of freezing.

Prevention

• To prevent against freezing, regularly clean and vacuum all filters and vents. Clean any drainage pipes or openings on the unit. Some window air conditioners are required to be installed at a slight downward angle so that the water drips outside. When the outside temperature is lower than 65 F, turn the air conditioner off.