Air Conditioning Evaporator Coils

An evaporator or evaporator coil is a part or an air conditioning system and is sometimes referred to as a cooling coil or indoor coil. Liquid refrigerant or Freon travels through a sealed copper tube and into the evaporator coil and then goes through a very tiny hole or metering device causing the liquid's pressure to drop significantly. This causes the refrigerant to expand which turns it into a low temperature, low pressure gas. By spreading out the molecules the temperature of the gas drops to just above freezing. This gas then absorbs heat from the air traveling across the coil which is pulled in through the return air and into a sealed duct system by the indoor fan.

An air conditioner not only cools the air but adds to the comfort level by dehumidifying or taking the moisture out of the air. Moisture condenses on the indoor coil like it does on the outside of a glass of ice water on a hot, humid day. As the warm air passes over the coil and is cooled it can't hold the same amount of moisture. The extra moisture is then carried away through a drain which is usually designed into the evaporator coil. From there it goes into a septic system or water trap. Sometimes the drain lines may become clogged which can result in water leaks in your ceiling or walls. An annual air conditioning inspection is a great way to keep your system is running smoothly and to keep drains clean.

An evaporator can come in several designs which vary with the type of installation. In a fan coil the evaporator is a part of the larger system. In a upflow or vertical installation a A coil is the most common configuration. Its called an A coil because is shaped like the letter A with the air blowing in through the bottom and out through the top. A vertical or box coil is the usual choice for a vertical system and typically has a built in drain pan with an external drain pan or emergency pan for safety.