Category - Air Conditioning
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Will Scholfield, Engineer

31 Jan : Updated 15 Apr ● 4 min read

What does the evaporator coil do in an air conditioner?


Air conditioning units found in homes in the UK have various parts and mechanisms that allow them to do their job of keeping you cool. The evaporator coil is one of the key parts of the air-con system. If it breaks or starts to work less efficiently, this will, unfortunately, affect your whole unit and prevent it from working as it should, so it’s important to understand what it does and how to maintain it. 

What is the evaporator coil?

Split system air conditioning units, like those sold by us at BOXT, have two units that comprise the system. There’s the outdoor unit containing the compressor and condenser coil, and the indoor unit housing the filter, fan and arguably the star of the show, the evaporator coil. 

The evaporator coil is located near the system fan in your indoor unit. It’s an upright structure usually in a shape resembling an ‘A’, comprised of panels and coils made from metals like copper, aluminium or steel due to these metals being good heat conductors. The coiled tubes on the panels of an evaporator coil are also lined with metal fins so the heat from the air can get as close as possible to the refrigerant within the tubes to maximise heat absorption and the cooling effect. 

What does the evaporator coil do?

In a split system air conditioning unit, refrigerant liquid flows between the two units, with the evaporator coil having the role of using the cool refrigerant to absorb the heat from the warm air that’s drawn in from your home. This is a continuous process of absorbing heat from the air to cool it down until your air conditioner detects that your room has reached the desired temperature or you switch off your unit.

It’s a lot more complex than this, though, so let’s go over the process the evaporator coil uses to cool your home in more detail. 

  1. The compressor pulls the liquid refrigerant into and through the metal-lined tubes in the evaporator coil.
  2. The liquid refrigerant passes through the expansion valve, which relieves the pressure from the liquid, lowering its temperature and making it cool. 
  3. The expansion valve then releases the cooled refrigerant in a controlled manner helping your air conditioner function efficiently.
  4.  The cooled refrigerant, once released by the expansion valve, absorbs the heat energy from the warm air that’s brought in from your room’s climate and blown over the evaporator coil’s tubes.
  5. Once the refrigerant has absorbed the heat, it evaporates, hence where this part gets its name!
  6. The remaining water vapour from the household air condenses into a liquid that drains into your unit’s condensate pan and is transported to be disposed of outside your home.  

How can you maintain your evaporator coil?

Due to the evaporator coil being such a prominent part of an air conditioning unit, routine maintenance is essential to ensure it’s functioning as it should, and your overall air-con system can run as efficiently as possible. 

You should ensure you stick to:

  • Regular cleaning

The coils on your evaporator coil need to be kept as clean as possible to perform at optimum efficiency. Even a thin layer of dust build-up can impact your coils ability and cause your system to use more energy than usual to do the same job. Dust or grime can cause the coils heat absorption and cooling capacity to be limited and reduced, costing you more in energy bills and increasing your carbon footprint, so it’s worthwhile keeping it clean. 

  • Servicing 

As well as regular cleaning, you will also need to book in for at least one annual air conditioning service, and where possible, a few services a year to keep on top of the maintenance of your unit’s internal parts. Due to airborne chemicals in your home caused by new carpets, upholstery, air fresheners and cleaning products, evaporator coils can develop tiny leaks due to corrosion. Having regular services carried out by a professional will ensure you identify these as soon as possible and resolve them. 

Read: How to repair an evaporator coil

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