Plenty of HVAC terminology can seem arcane and impenetrable to those without experience, but there's one problem that most people understand: frozen evaporator coils. As the name implies, this issue describes actual ice formation on the evaporator. Since moisture condenses from the air around your evaporator coils, various conditions can lead to that moisture freezing and forming a layer of ice.

Unfortunately, ice is bad news for your air conditioning system. Ice will prevent the evaporator coils from absorbing heat and may cause the compressor to overwork and shut down. Contrary to popular belief, a well-maintained AC system won't freeze up simply because it's working hard. Instead, a frozen evaporator coil is always due to one of these three underlying issues.

1. Low Refrigerant Pressure

Your air conditioner's refrigerant acts as a heat transfer medium, but the mechanics of heat transfer can be surprisingly complicated. One particularly confusing aspect relates to pressure and temperature. Although it may seem counterintuitive, lower pressure at the evaporator coil will result in lower temperatures. If your system is low on refrigerant, you'll starve the evaporator.

Typical air conditioning units will produce a temperature at the evaporator coil above freezing. This design maximizes efficiency and eliminates any chance of condensation freezing on the coil. If your system is low on charge due to a leak, the low pressure at the coil will reduce its temperature, causing condensation to freeze on the coil.

2. Refrigerant Restrictions

Modern air conditioning systems include metering devices that ensure refrigerant enters the evaporator coils at the appropriate pressure. A typical metering device has an inlet on the high side and several distribution tubes leading into the evaporator on the low side. These devices include mechanical components, so they can fail or become clogged if contaminants enter the system.

As a result, a restriction (typically at the metering device) is another way to reduce evaporator temperature. Although the system has enough refrigerant, a restriction will reduce its flow into the evaporator. This problem effectively creates the same effect as low refrigerant, causing the evaporator coil to freeze.

3. Airflow Restrictions

Airflow is another critical component in keeping your evaporator at an appropriate temperature. Airflow over the evaporator distributes cool air throughout your home and brings warm air to the coils. Without adequate airflow, the temperature around the evaporator will drop since the already cool air will linger in place.

This situation is similar to a refrigerant restriction, although for a different reason. Without a steady supply of heat energy, water that condenses around the coil will eventually freeze, ultimately causing your entire AC system to freeze up and stop working.

Contact an AC repair service to find out more.