Why is my AC freezing up? How to Fix

If you ever find a frozen evaporator coil ( inside unit )  or you notice the refrigerant line going to your condensing unit outside is iced up, you have a problem. Shut your AC off and read the tips below.
If your AC system is freezing up, it’s important to correct the issue to prevent potential damage to your compressor. Compressor replacement is one of the most costly repairs on a homeowner’s AC system.

What causes your AC to develop ice?

A majority of icing issues are related to airflow issues. If the volume of air across the evaporator is low or restricted, the refrigerant in the system absorbs less heat from the surrounding air. The temperature of the refrigerant in the system drops to below 32 degrees – the freezing point of water. The humidity ( moisture) in the air slowly starts to freeze on the surface of the evaporator coil & ice forms. As the ice starts to form, it causes further airflow restriction & accelerates the ice formation.

Iced evaporator coil

How to thaw ice from equipment

Regardless of why the ice formed, the first step is to fully clear before correcting the problem. This can sometimes can take hours, depending on the severity. It is important to clear all the ice.* We are assuming a bad blower motor is not the reason for icing

  1. Adjust the thermostat setting from cool setpoint to the “Off ” position
  2. Adjust the Fan setting from ” Auto ” to the “On” position. The indoor fan will remain on constantly in this position. Make sure to return to the previous setpoint when finished.

What this does is shut the AC cooling off but allows the air handler fan only to operate. This allows the warm indoor air to accelerate the melting of the ice. Be aware that if the coil is heavily iced, some water may drip off the face of the coil as it thaws out. This is normal but if excessive, you may want to use a couple of towels or a wet-dry vac to suck up to prevent flooring damage, etc.

** This Tip would not apply if the indoor fan motor has failed – Typically it is pretty obvious the blower motor is operating. You can hear the operation or may feel some airflow. If the motor is not operational, simply leave everything off and call for a repair.

Most common reasons for system icing

  • Dirty Filter
  • Dirty evaporator coil
  • Ductwork issues 
  • Bad blower motor
  • Defective expansion valve
  • Low Refrigerant

Dirty filter

A very dirty filter can restrict ( slow ) airflow enough to allow the evaporator to form ice. Again, once the ice starts to form, it exacerbates the situation. Often once the ice is clear, just changing the filter will remedy the situation. Check the cleanliness of the evaporator at this point. Most systems have a small 1″ door where the filter is located. Look up under ( from the filter side) the evaporator coil from this filter location to see if significant dirt is on the coil. If ductwork is in your way, a cell phone can be used to snap a picture of the coil to confirm. If the coil is very dirty it may need to be professionally cleaned to restore proper function.
* Be careful not to drop your cell in the ductwork.

Dirty Evaporator

 If you’re not frequently changing the air filter, dirt can bypass and get embedded on the evaporator coil itself. This is pretty common. A dirty evaporator coil causes airflow restriction and loss of heat transfer to the refrigerant in the system.
Depending on how your system is configured, it may be possible to clean the coil yourself. Coil cleaner can be purchase online or at a local home store. Make sure you buy the appropriate cleaner designed for evaporator coil cleaning, Using the wrong product can damage the fin surface of the coil. This cleaner along with a nylon type dish brush to scrap the heavy dirt off may be sufficient to correct the problem.
** Be extremely careful not to bend the fin surface of the evaporator. You need to brush in the direction of the fins to prevent bending & damage. It can be very costly to replace the entire coil if damaged.
Depending on how dirty the coil is, it may be required to have to coil professionally cleaned. This may involve removing the entire coil to chemically clean.

Dirty evaporator coil

Ductwork issues

Damaged supply or return ductwork, or sometimes just improperly sized, also can cause enough airflow restriction to cause ice formation. All HVAC systems are designed to move a rated specific amount of air.Homeowners often inadvertently damage ductwork crawling around in the attic. Cable guys are notorious for damaging ductwork and leaving.

Bad Blower motor

If the interior blower motor stops operating – there is no airflow. Your system will ice up immediately. Blower motors do fail, but often it is only a run capacitor ( depends on the type of motor) that is required for the motor to operate. This usually requires a professional to correct.

Defective Expansion Valve

There is a refrigerant metering device located in the air handler. A TXV style metering device can fail or gets weak & not meter the correct amount of refrigerant to the evaporator. This can cause a condition that causes an icing situation. Professional service would be required to determine & correct.

Low Refrigerant / Leak

Loss of refrigerant is a very common reason for system icing. The Freon or refrigerant in the system is a chemical that has a consistent pressure/temperature relationship. For example, R-410 refrigerant at 120 PSIG correlates to approximately 40-degree refrigerant temp. This would be OK but if the system loses refrigerant and the pressure drops to say 96 PSIG the refrigerant temperature is 29 degrees – below freezing point – Icing can occur.

While there are other reasons for ice to form, these are the most common culprits. Give us a call if we can help! 727-392-6111.