Six Common Symptoms of A Dirty Evaporator Coil

An air conditioner is an integral part of many homes. However, most homeowners only consider the components of their AC unit when something goes wrong.  

A dirty evaporator coil in your HVAC system can lead to multiple problems, including reduced cooling efficiency, increased energy consumption, and potential damage to the equipment. It can even affect the air quality in your home and, consequently, your health.

Here’s our list of the six most common dirty evaporator coil symptoms.  

1. Reduced cooling performance

Reduced cooling performance is one of the most noticeable signs of a dirty evaporator coil. If your air conditioner is not cooling your home as effectively as it used to, or if you notice warm air coming from the vents, it could be a sign that your evaporator coil needs cleaning. 

Dirt on your AC unit’s evaporator coils reduces the surface area available for heat transfer. This accumulated dirt and debris then acts as an insulating layer that inhibits the coils’ ability to absorb heat effectively from the indoor air. 

As dirt and debris accumulate on the coils’ surface, it can restrict air passage, reducing the amount of air that comes into contact with the coils. This will then result in reduced airflow through the evaporator coils, leading to lower cooling performance and reduced air circulation in the room.

As a result, the cooling capacity of the AC system is diminished, and your unit may struggle to cool the air to the desired temperature, leading to reduced cooling performance and higher monthly bills.

2. Increased energy consumption

A dirty evaporator coil can cause your HVAC system to work harder to maintain the desired indoor temperature, increasing energy consumption. If you notice a sudden spike in your energy bills without any other explanation, your evaporator coil could be a potential culprit. 

Here are some causes of increased energy consumption: 

An overworked system 

The evaporator coils in an air conditioning system absorb heat from the indoor air, which is then transferred to the refrigerant for cooling. When the evaporator coils are dirty and coated with dust, dirt, or debris, it acts as an insulating layer that reduces the efficiency of the heat transfer.

As a result, the AC system has to work harder and consume more energy to achieve the desired cooling effect, leading to an increase in energy consumption.

Reduced cooling capacity

In addition, when dirty AC coils restrict the airflow through the coils, it reduces the overall cooling capacity of the AC system. The system compensates by running longer cycles to meet the cooling demand. 

This prolonged operation increases energy consumption as the system has to work harder to maintain the desired indoor temperature. These longer run times mean more energy consumption, which, in turn, results in higher energy bills.

Your system is trying to maintain the refrigerant pressure 

Finally, when it comes to energy consumption, the compressor in an AC system is responsible for compressing the refrigerant to raise its temperature before it is sent to the condenser coils for heat dissipation. 

When the evaporator coils are dirty, the compressor may also have to work harder to maintain the required refrigerant pressure and temperature – yet another reason for increased energy consumption.

3. Frequent system cycling

Another symptom of a dirty evaporator coil is frequent system cycling.

If you find that your HVAC system is turning on and off more frequently than usual, it could be due to reduced cooling efficiency caused by a dirty coil. Consequently, the system may then struggle to reach the desired temperature, leading to frequent cycling as it tries to compensate for the reduced heat transfer. 

Also, when the evaporator coils are dirty, pressure and temperature differentials across the coils can increase. This can cause the system to cycle more frequently as it struggles to maintain the proper pressure and temperature levels for efficient operation.

This frequent cycling can put a strain on the compressor and other components in your air conditioning system.

4. Ice formation on the coil

A dirty evaporator coil can also cause ice to form on the coil itself. 

How? The dirt on the coils can restrict airflow across the coil surface, reducing heat absorption from the air. As a result, the temperature of the evaporator coils may drop below freezing, causing moisture in the air to freeze on the coil surface and form ice. 

This ice buildup can further block the airflow and reduce the cooling capacity of the AC system. Ice on the evaporator coil can further reduce the system’s cooling efficiency and potentially damage the coil.

5. Unpleasant odors

If you notice unpleasant odors coming from your HVAC system, it could be due to a dirty evaporator coil. Moisture can accumulate on the coils, a perfect environment for mold and mildew to grow.

Mold and odor-causing bacteria

Mold and mildew have distinct musty odors that can be released into the air as the AC system circulates the cooled air. These odors can be unpleasant and can also have adverse effects on indoor air quality, potentially causing respiratory issues and allergies.

In addition to mold and mildew, bacteria can also thrive on dirty evaporator coils in AC units. Bacterial growth can produce foul odors that will be distributed throughout the house. 

These odors can range from musty to rotten smells, depending on the type of bacteria present and the extent of the growth.

Build up and decay of organic matter 

Another reason for unpleasant odors can be the accumulation of organic matter in the dust and dirt on your evaporator coil. Over time, this organic matter can decay and produce foul odors, which can then be circulated into the indoor air by the AC system. 

These odors can be unpleasant and may give off a stale or rotting smell.


A third reason for unpleasant odors coming from your AC is volatile organic compounds (VOCs). VOCs are chemicals that can be emitted from various sources, such as cleaning products, paints, and furnishings, and they can accumulate on evaporator coils. 

When the AC system is running, the VOCs can be heated and released into the air, resulting in unpleasant odors. VOCs can also negatively impact indoor air quality and may cause health concerns.

6. Increased dust and allergies

Is your evaporator coil dirty? This can also lead to increased dust and allergens circulating in your home. 

As the coil becomes dirty, it can trap dust, pollen, and other allergens, which can then be blown into your indoor air when the system is running, potentially exacerbating allergies or respiratory issues.

Does your AC unit need cleaning? Contact Anderson Air.  

If you notice any of these symptoms, it’s crucial to have your HVAC system inspected and maintained by a qualified HVAC technician. 

Regular cleaning and maintenance of the evaporator coil can help improve cooling efficiency, reduce energy consumption, and prolong the lifespan of your HVAC system.

Call Anderson Air today and discover how our friendly technicians can help clean and maintain your AC system for cleaner, healthier air.

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