Evaporator coils of the air conditioner hold refrigerant that is in liquid form and turns the cool liquid into gas to make warm air cool, which the AC blows into the house. If the evaporator coils of your HVAC freeze up, your AC won’t cool the house and you may require the help of HVAC repair services. These are causes of a frozen evaporator coil.

Dirty Air Filters

The reason for many AC problems is dirty or clogged air filters because they allow better airflow. Moreover, air filters in mini split ACs are used for keeping the evaporator coils cleaner. When air filters collect dust, they become clogged and the airflow is restricted and evaporator coils freeze up.

You should clean or replace the air filters of your HVAC unit every month and during the peak summer and winter months, you should clean or replace the air filters every two weeks for getting the best efficiency.

Dirty Evaporator Coils

When the AC condenser unit and the ducts or the indoor unit are not cleaned frequently, dust and dirt settle on the air filters and the evaporator coils. This can lead to the freezing of the evaporator coils. Moreover, it will also stop the AC from cooling the house.

Therefore, clean your ACs evaporator coils every 3 months. Keep in mind that evaporator coils are present in the indoor unit or air handler of a mini split whereas, in the case of HVAC units, evaporator coils are present inside the condenser unit.

Clogged Drain Pipes

As evaporator coils cool the warm air, condensation occurs. This water is directed towards the drain pipes that lead to a floor drain inside or outside the house.

Dust and dirt build up inside the drain pipes because the air that condenses into water contains dust particles as well. Moreover, drain pipes can be clogged due to mold or algae growth. When drain lines become clogged, condensed water can’t flow out of the unit and cause water leakage and freezing of the evaporator coils.

For cleaning drain lines of your HVAC, you can use a vacuum to suck dirt out of the drain pipes. You should also use bleach to clean the drain pipes once a year.

Outdoor Temperature Is Too Low

Evaporator coils can freeze up if your AC is in cooling mode and the air outside is already cold. This is because evaporator coils make warm air cool during cooling. When the air that it has to cool is already cool, evaporator coils may freeze up.

So, check the outside temperature and if it’s low, there is nothing wrong with your AC. You can thaw the ice by running only the fan of the AC. If you have a heat pump, you should run it in heat mode for a few minutes.

Low Refrigerant Levels

The refrigerant flows through the evaporator coils to cool the indoors through the air handler or air ducts. If there is insufficient refrigerant, the AC will overwork to make up for the low refrigerant. This may increase condensation and also freeze up the evaporator coils.

This should be kept in mind that refrigerant levels don’t reduce often. So, the cause of low refrigerant is usually a leakage of the refrigerant or the AC wasn’t charged with the refrigerant to the correct levels.

Faulty Blower Fan

The blower fan keeps the temperature inside the condenser unit in check to keep air flowing around the evaporator coils. If the blower fan stops working due to a malfunction, air can’t flow out of the unit and cold air can also get trapped inside the unit freezing up the evaporator coils. Have a professional check your unit if the blower fan of the unit is busted.

Malfunctioning Thermostat

The cause of freezing coils can be a faulty thermostat as well. If the thermostat isn’t sensing the temperature correctly, the AC will run for much longer. As the HVAC unit will overwork, it may produce ice on the evaporator coils.


Many causes of the icing up of evaporator coils are due to a lack of AC maintenance. Make sure to clean your AC components regularly to avoid this issue and hire an air conditioner repair service DC once every six months for maintenance.