Understand What An Evaporator Coil Is And How To Fix Common Problems

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How Does Your Air Conditioner Work And The Early Signs Of Common Problems

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Most of the problems experienced with air conditioners can often be contributed to the evaporator coil.

Understanding what an evaporator coil is and how it operates will go a long way towards helping you diagnose and fix your air conditioning unit in order to enhance its efficiency and prolong its lifespan.

What is an Evaporator Coil?

The first step is to study the basic components of an evaporator coil, where it is situated in the air conditioning unit, and what its function is.

The evaporator coil forms an integral part of an air conditioning unit. Its function is to absorb heat from the air and turn it into cool air. It is either attached to the furnace or located inside the air handler. Its appearance is similar to that of a car radiator. The evaporator and condenser coils work together to perform the task of heat transfer that produces a cooler internal environment.

In the next section, we will get into more detail about the basic function of an evaporator coil and how it works to cool the air in your home.

How Does An Evaporation Coil Work?

A split-system air conditioning unit contains a closed-loop refrigerant system that contains coolant. Refrigerants are high-heat absorbing chemicals with unique properties capable of continuously changing state under pressure from vapour to liquid and back again.

The function of the evaporator is to extract heat from indoor air and expose it to the refrigerant circulating through the copper tubes of the coil. By the time the refrigerant reaches the evaporator it has a consistency of 80% liquid and 20% vapour.  The copper tubes maintain a cold vapour state of around 40 degrees that maximizes the heat-absorbent properties of the refrigerant. As the coolant travels through the coil it absorbs heat from the hot air constantly flowing over the evaporator. The effect is heat transformation known as latent heat transfer.

What is Latent Heat Transfer? Also known as heat transformation, it refers to the heat evaporated by a unit of mass. During this process of evaporation there no increase in temperature is recorded, however, the heat is transformed into vapour.

Once the refrigerant inside the coil is completely transformed into a state of vapour it undergoes a super-heating process. The vapour then performs a complete cycle, returning once more to the compressor and through the condenser where it is transformed back to its original consistency of 80% liquid and 20% vapour. Because it is a low-pressure coolant it can undergo the same process again and again, while continuing to cool the air that flows through the AC.

What happens if the evaporator coil is dirty?

The evaporator coil is the part of your air conditioner that cools the air. If it’s dirty, then you’re paying for air that isn’t clean. Dirt and dust getting into your cooling system can also damage parts like compressor and condenser coils, which are expensive to fix. If you don’t want to pay higher utility bills and be forced to replace parts, you need to clean your evaporator coils regularly.

Some Common Problems that can occur with an Evaporation Coil

Once you have a basic understanding of the purpose and function of an evaporator coil, you are in a better position to troubleshoot possible problems. Below we list a few of the most common evaporator coil problems to look out for:

1. Frozen Coil

As strange as this may sound when an evaporator coil becomes frozen it will affect the capacity of the air conditioning unit to cool the air effectively. The reason, while this may sound counter-intuitive, is that the main function of the refrigerant (which is to absorb hot air) is interfered with by a formation of ice on the outer tube. A film of ice acts as insulation that prevents hot air from being absorbed. If ice has accumulated on the outer tube of the coil the air conditioner will continue to run but it will not produce the desired cooling effect.

How to Fix a Frozen Coil

Proper airflow is essential for an air conditioner to work properly. When airflow is limited or restricted it will affect the balance of the operating system the air conditioner relies on. The first thing to do is to find out what is limiting or restricting the unit’s airflow.

The most obvious thing is to look for anything that is blocking the airflow like damage or kinks in the tubes. This is often found when an air conditioner has recently been installed incorrectly.

The second most common reason may be a low level of coolant so check the refrigerant level to make sure there it is adequate coolant in the unit.

2. Leaking

If there is a leak it can usually be detected to the coil. A leak in the unit will obviously affect the balance of the system. When the system has been thrown off balance the unit will automatically work much harder, placing additional pressure on the AC motor which will eventually cause more serious problems.

How to Fix a Leaky UnitIf you discover a leak in your air conditioning unit you should have it fixed immediately. Refrigerants are made from highly poisonous chemical compounds that should not be touched or breathed in as they can cause damage to the skin and serious respiratory problems. These chemicals are highly dangerous to humans, animals, as well as the environment and should be treated as such. Do not procrastinate when dealing with this problem.

In addition to the health and environmental problems, leaked refrigerant can also damage your air conditioner. It will corrode the outside of the coil that will cause wear and tear, limiting the lifespan of the air conditioning unit.

Fortunately, leaks are easy to detect if you inspect the unit regularly. If you do find a leak it is imperative not to try and fix it yourself but to call a professional air conditioning expert to deal with it as soon as possible in order to prevent any health risks from occurring.

3. Dirt and Debris

While it may seem obvious, you will be surprised at how many air conditioning units are allowed to become suffocated with accumulate dirt and debris. As you have probably discovered by now, an evaporator coil cannot perform properly if it is coated with ice. This also applies to dirt and debris. While the coil will not be adversely affected by a light coating of dust, if too much dust and dirt are allowed to accumulate on the outer tubes it will insulate the coil the same way that ice formation does, preventing the coil from properly absorbing heat and transforming it into cool air.

How to Fix a Dirty Coil

Cleaning the evaporator coil should be part of the regular maintenance of your air conditioner. Fortunately, this is an easy task to accomplish. First remove any visible dust and debris like leaves, bits of grass and stray plastic which are some of the more common things found around coils.

There is no shortage of advice on how to clean an evaporator coil. Always switch the power off before cleaning. Basically, it involves using a spray cleaner and a soft brush to gently brush the dirt from the coil. After cleaning, hose down the coil and allow it to dry before switching the unit back on. If the evaporator coil is cleaned regularly at the beginning of each season, it will help prolong the life of the unit and improve its efficiency. A clean coil will also help reduce the running costs of the unit.

Can the air conditioner evaporator coil be repaired?

Yes. The most common repairs are: Cleaning out the dust, Cutting and re-welding fins that have become bent due to improper transit or installation of the AC unit, Straightening a coil that has been dented in transit or damaged by poor handling or installation by another contractor. However, this is usually not recommended. The coil is usually the least expensive part of an AC system compared to the repair cost and the service call. If the coil leaks, it is generally cheaper to buy a new one than to repair it.

Is it normal for evaporator coils to be wet?

Yes. It is usual for evaporator coils to be wet because humidified air can’t escape the evaporator coil without condensation forming at the low point where the water droplets are drawn off by a small blower fan and exhausted outside.

How long do AC evaporator coils last?

AC evaporator coils last between six and 15 years. If AC coils are doing their job, they will be getting dirty and should be replaced at least every 10-15 years. In some cases, coils can last for up to 20 or 30 years. Keeping the coil clean will help extend its lifespan. Any dirt buildup on the coil could cause it to overheat, leading to the deteriorating of electrical components and overheating that may cause fires in your home! A periodic check of your heating equipment is advised to ensure proper operation and safety!


We hope this brief article has served as an introduction to help you understand the function and operation of an evaporator coil and that it will help you recognize and fix the most common problems associated with it. We wish you a cool season!

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