How do Condenser & Evaporator Coils Work?

  • Air Conditioning

When you hold your hand up to a vent or feel the intake of air at your air conditioner's filter, you can feel how rapidly it circulates air through your home. Another substance, coolant, also flows through its own closed system within your air conditioner. That hidden system holds the key to how your AC unit cools your home.

Air conditioners and refrigerators rely on a fundamental property of gases to cool the surrounding air. As pressure on a gas decreases, the gas expands and cools; increasing pressure makes the temperature rise. You could also express these phase changes as evaporation and condensation, which is how evaporator coils and condenser coils get their names. Refrigerants, including Freon and Puron, may never need recharging throughout the life of your AC.

The coolant in the system travels through four components:

  • An expansion valve to reduce the pressure on liquid coolant
  • An evaporation coil where the coolant can become gaseous, absorbing heat from surrounding air
  • A compressor that pressurizes the gas
  • A condenser coil in which the heated gas becomes a liquid, releasing its heat to the outside air

The blower moves warm indoor air over the chilled evaporator apparatus as the exterior exhaust fan moves hot air away from the heated condenser coils. All air conditioning systems, including window units, heat pumps and ductless units, operate on the same principle. They differ only in the size and configuration of the coils.

Evaporator Coils

You might think of your air conditioner as adding cool air to your home, but it's more accurate to say that your AC unit subtracts heat from indoor air and transfers it outside. That transfer takes place in the evaporator coils on the interior half of your air conditioning system. As the coolant inside the metal coils evaporates, it acts as a heat sink for the air that moves across it from the blower. Copper conducts heat readily, so the coils that contain the coolant are usually made of this metal. To maximize surface area and provide more cooling power, the copper coils have metal fins or vanes surrounding them. In a dual or hybrid heat pump system, the same coils that act as evaporation sites in the summer to cool your home become condensation sites in the winter to provide warmth.

Keeping the coils clean is vital to proper heat exchange. When dust and debris collect on coils, the particles form an insulating layer that prevents warm household air from the blower from reaching the chilled metal. If you smoke or cook frequently, you may need additional cleaning power for dirty coils. Investing in quality air filters may save you challenging cleaning jobs in the future.

Just as a glass of iced lemonade develops beads of condensation on a hot, humid day, evaporation coils can collect droplets of water. Cooled, conditioned air can hold less water vapor, so the remaining water condenses on the coil's surfaces. Drain pans normally collect the condensation and move it outside your home, but a clogged drain can cause water leaks. Interior coils can also freeze up if they become too cold; it may seem strange that ice makes your air conditioner less efficient, but iced coils cannot transfer heat effectively and should be allowed to thaw before turning the unit on again.

During routine seasonal maintenance, your AC service cleans the interior coils for you, but if you notice reduced cooling capacity, check the coils for signs of dirt or ice. A brush and a commercial coil cleaning spray can remove the worst of the soil, but turn off the power to the unit before attempting to clean the coils. If you feel unsure about working with your AC unit's coils, call a professional instead of trying to do the work yourself and risking damage to delicate metal vanes.

Condenser Coils

Your air conditioner's condenser apparatus is outside where waste heat can dissipate to the outdoor air as the heated gas inside it returns to its liquid state under pressure. Like the interior coils, the exterior coils are a heat transfer site; in this case, though, the heat moves in the opposite direction, going from the coolant into the surrounding air with the help of exhaust fans.

Like evaporator arrays, condenser arrays typically contain copper or other metals that easily transfer heat. Their vanes are built into the exterior unit to facilitate cooling. Your air conditioner runs more efficiently when excess heat leaves the system quickly, so keeping the coils clean can lower your utility bills and lengthen the lifespan of your system.

Outside units are susceptible to collecting dust, pollen and other debris, but they are easier to clean than interior coils. A stiff nylon brush, a can of commercial cleaning solution and a hose are usually sufficient to remove any build-up of dirt. As with interior unit cleaning jobs, turn off power to the unit before cleaning the vanes, coils and grill. If the unit has not been cleaned in some time, it's best to call a professional AC service to clean the coils thoroughly.

For the first time cleaning interior or exterior coils, calling HVAC specialists such as the certified technicians at Air Conditioning Southeast is a good idea. Your technician can give you tips on keeping coils clean and free of debris and help you devise a maintenance schedule to make your AC run at peak efficiency.