The most common reason for frozen evaporator coils is insufficient airflow. This is commonly caused by a clogged or dirty air filter, backed-up drain clogs, low fan speed, or a dirty evaporator coil. Check to see how many registers are closed in your home.
Clean or Replace Your Air Filter
If your AC system's evaporator coil isn't getting enough airflow through the air duct, ice will eventually begin to form along the coil. Luckily, this can be prevented, as you should be inspecting and changing or cleaning your air filter routinely regardless.
While icing due to low refrigerant is rare, and often requires other problems, it can happen. Because the pressure in the evaporator is so low, the boiling point of the refrigerant is well below 32°F. This causes the coils closest to the metering device to be very cold, which causes moisture to freeze.
Adding more refrigerant is a temporary fix, but you'll continue to see poor air conditioning efficiency until you fix the underlying problem. In most cases, it's more cost-effective to get a new coil than repair an old one.
#1: Dirty air filter
A dirty filter can lead to a dirty evaporator coil and potentially a frozen evaporator coil. Prevent a clogged filter by changing your air filters regularly. This should be every 30-90 days depending on the quality of the filter, how hard your system is running, if you have pets, and other factors.
But when you go outside to see if your system is running, you see ice on your lines and coil. How is that possible? If this happens to you, then your evaporator coil is most likely frozen, which means that all that freezing cold refrigerant is flowing into the outdoor lines (causing them to also be covered in ice).
If mold and grime fill the drain, it also causes water to flow backward into your evaporator compartment. Since the evaporator coil is the coolest during a cycle, nearby water will freeze, almost instantly forming ice crystals.
1st Step: Turn Your HVAC Unit Off.
Even if it's sweltering outside, you still need to turn OFF your air conditioner! Running a frozen air conditioner will wear out parts much faster, and could overheat your unit. Worn parts are bad news for the most expensive piece of your HVAC unit—the compressor.
How Often Do I Need to Change Out My Air Filter? Generally, most air filter manufacturers and HVAC companies recommend changing your air filter every 90 days, or 3 months. That can change based on where your home is located (ex. dusty, dry climates), if you have any pets, and the age of your system and equipment.
Dirty coil
Over time, your system's evaporator coil will become covered in dust, dirt, grime, and more. This prevents it from getting the airflow it needs to properly move heat, which means that the system could then freeze over.
Turn the Thermostat Fan Setting to On. Turn your thermostat fan setting to “On” so that the fan continues to blow air over the coil. The warm air in the home will naturally defrost the frozen coil. In severe cases, the heat can be turned on to speed up the process.
While the refrigerant in your vehicle can escape even without a leak, it's often not enough to cause significant issues unless you've failed to top up the refrigerant for years. When the lack of refrigerant becomes significant though, it can cause a number of problems, including an overheating driver in the summer sun.
Most ACs nowadays come shipped from the manufacturer with the exact amount of refrigerant that it will need for the duration of its life. So, unlike a car, your AC won't ever need to “fill up” on refrigerant unless something goes wrong with the system.
An AC leak will lead to warmer air from your vents over time. In most cases this can be fixed with a proven stop leak additive to seal up any leaks. When it's time for an AC recharge, turn to AutoZone.
The most common reason for this is that the air conditioner is getting insufficient airflow, which is commonly caused by clogged air filters, backed-up drain clogs, or a low fan speed. When there's a lack of airflow, there won't be enough heat to prevent the condensation on the evaporator coil from turning into ice.
Use a can of compressed air (which you can purchase at any hardware store) to gently blow large particles of debris and dirt out of the evaporator coils. Any debris that is stuck can be worked away using your soft bristle brush. Make sure you are not using a metal or wire brush because it can damage the coils.
Brush Off Loose Debris: Using a soft brush or a specialized furnace coil brush, gently brush away any loose dirt or debris from the coils. Be gentle to avoid bending the fins or damaging the coils. Vacuum the Coils: Attach a soft brush to your vacuum cleaner and carefully vacuum the coils.
Low refrigerant can also lead to frozen evaporator coils. Without refrigerant passing through the coils, there will be no way for that absorbed heat to be transferred out of the air handler. The lack of pressure within the coil continues to drop, the moisture freezes onto the coils, and ice forms as a result.