2 Reasons Why Your Central Air Conditioner's Evaporator Coil Is Freezing

You've not only seen water leaking from the lower sections of your air ducts, but also noticed a strange, musty odor drifting throughout your home. These are telltale signs that your evaporator coil—the part of your air conditioner that cools air— is freezing. However, you're not quite sure what's causing it. Here are the two main issues that will cause a frozen evaporator coil:

Clogged Air Filter

Your evaporator coil must receive a large volume of air to provide cooling to your home. A well-maintained air conditioning system can operate for hours without developing a frozen evaporator coil since it continually receives a high volume of warm or room temperature air. However, when there isn't enough air flowing through your air conditioning system, the ice-cold refrigerant flowing through your coil will freeze the condensation that collects on the coil during use. In most cases, restricted airflow is caused by a dirty air filter.

Your air filter, whether electrostatic or conventional, is the first component through which air must pass to reach your evaporator coil. If your filter is clogged with pet hair, dust, and other similar types of debris, then it will significantly reduce the airflow throughout your entire system.

The amount of time you use your air conditioner, the cleanliness of your home, and even the number of pets you own will determine the interval at which your air filter needs to be cleaned or replaced. Generally, you should replace your air filter every other month during periods of heavy usage to avoid clogging. 

Malfunctioning Motor

As you well know, air doesn't magically flow through your air conditioner—instead, it's pulled through your central air system by your blower motor. However, if your blower motor is producing a constant hum or burning smell, then it's likely burning out and providing inconsistent airflow to your central air system.

Debris that enters your central air system through your air filter or other entry points can settle on your motor and prevent it from cooling properly. During extended periods of use, inadequate cooling eventually causes your motor's electronics to burn out and malfunction.

To fix this issue, you'll need to perform or arrange for blower motor cleaning. However, if you've continued to regularly use your central air system while your blower motor is malfunctioning, then a cleaning won't fix your problem. In such a case, your motor's electronics are likely fried and need to be replaced by an HVAC technician.

If you have electrical experience, then it's possible for you to clean your blower motor by yourself. Just follow these steps:

  • Blower Motor Cleaning

    • Shut off the power to your central air system and open the access panel on your blower motor compartment. While wearing insulated gloves, begin disconnecting the wires that lead from your air conditioner to your blower motor. If necessary, label each wire to avoid confusion while reinstalling your motor.

    • Take your motor into your yard and disconnect it from your squirrel cage (the large cylinder that surrounds your motor) by removing the three or four mounting screws from the sides of your cage.

    • Use a gas duster or your old air compressor to blast debris out of the motor. Additionally, clean your squirrel cage by washing its interior with your garden hose.

    • Dry your squirrel cage before mounting your motor back inside of it.

    • To finish the job, place your cage and motor back inside your blower motor compartment and reconnect the electrical wiring with wire connectors or solder.

Inspect your air filter and blower motor for clogging or debris. If either of them are dirty, replace or clean them and activate your air conditioner. If these components were the problem, then you'll notice that your evaporator coil no longer freezes and leaks water into your air ducts. However, if your evaporator coil is still freezing and causing problems, then you'll need to hire a professional HVAC technician—your air conditioners condenser or compressor will need to be replaced.