Your evaporator coil is the side of your air conditioning system that picks up heat from your home. Warm air travels through your return air ductwork, eventually passing over the cool evaporator coils and depositing its energy into the refrigerant. Problems with the evaporator coils can reduce system efficiency or stop your air conditioning from cooling your home altogether.

Fortunately, the evaporator is a relatively robust piece of equipment, but that doesn't mean it can't be a source of trouble. Keep reading to understand more about three common (and frustrating!) problems that can develop in or near your air conditioner's evaporator coil.

1. Galvanic Leaks 

Galvanic (or dissimilar metal) corrosion is a somewhat esoteric term that can have some surprising real-world effects. Air conditioning evaporator coils typically combine aluminum for the fins, copper for the refrigerant tubes, and galvanic steel for the framing elements. Unfortunately, these dissimilar metals can promote corrosion in the presence of moisture.

As a result, evaporator coils are a relatively common source of refrigerant leaks. In a worst-case scenario, these leaks may occur in the tubing located inside the fins. Fortunately, leaks are more common in brazed areas or joints, and these leaks are typically easier to repair. Leaks deep within the coil will often require replacing the entire unit.

2. Coil Freezing

Freezing isn't (always) the fault of the coils, but it is a problem that occurs at the evaporator. There's a direct correlation between refrigerant pressure and temperature, meaning that lower refrigerant pressure results in a lower temperature. If insufficient refrigerant reaches the evaporator coil, the temperature will potentially drop below freezing.

Once the coils become cold enough, you can expect an insulating layer of ice to form around them. This insulation stops the refrigerant from absorbing heat, ultimately reducing system efficiency and potentially causing other problems. If ice is forming on your evaporator coils, that's a sure sign that your system requires immediate attention.

3. Liquid Line Restrictions

Refrigerant enters your evaporator coil as a liquid but leaves it as a vapor. As the refrigerant picks up heat from the air in your ductwork, it undergoes a phase transition. This transition is crucial since liquids are incompressible, and liquid refrigerant will damage your compressor. However, it's also important that the liquid refrigerant enters your evaporator at the correct pressure.

A metering device (also called a thermostatic expansion valve or TXV) regulates the pressure on the liquid line right before the evaporator. This device can become clogged or damaged, creating a restriction in the line and reducing refrigerant pressure. A restriction at the TXV can potentially cause your evaporator to freeze or stop your system from absorbing sufficient heat to cool your home.

To learn more, contact an AC repair service.