HVAC Training – Mold on an Evaporator Coil

by Ron Walker

Many times during a maintenance visit you will find mold growing on the evaporator coil. Most HVAC technicians will immediately recommend an Ultraviolet light (U.V. light) to “take care” of the mold. While U.V. lights do help kill mold and other living organisms in an HVAC system, mold is a symptom of a problem not the problem itself. Make sure you explain this to the homeowner before you recommend a coil cleaning. Note – the coil cleaning is the FIRST step in eliminating the mold.

Mold growth gradually destroys what they are growing on. Mold can also create indoor air quality problems, damage furnishings, restrict airflow, and can be a health risk to occupants. Mold and mold spores are a natural part of our environment and given the right conditions mold will grow in an HVAC system. The key to remember, if you want to control mold growth control humidity.

A properly operating AC system will help control humidity under normal conditions. However, an AC system that is not operating properly will not properly control humidity.

The first step is to clean the mold growth off of the evaporator coil. Most of the time coils can be cleaned in place using a no-rinse evaporator coil cleaner. Follow these steps to clean an AC coil in place:

  • Turn off or disconnect power to unit being serviced, and remove any heavy or matted soils first.
  • Shake the can well.
  • Thoroughly saturate the targeted area with product.
  • Be sure foam evenly covers the entire surface.
  • With this self-rinsing formula, the foam will break and condensation will completely rinse the emulsified material.
  • You may wipe clean or rinse with water if desired or if using on non-condensation producing coils.
  • For extremely stubborn or heavy deposits, repeat applications may be necessary.
  • Turn on or return power to the unit.

AC coils that have been neglected or are hard to reach will have to be removed from the system and cleaned. I don’t recommend this step for HVAC systems where the coils are severely rusted. Coil replacement is a better option.

The most important step of helping eliminate mold growth is to determine the cause. Humidity in a home must be held below 55%, ideally 30% to 50%. If the humidity in the home is consistently above 55% there is a problem.

Here are some things to check on the AC system:

  • Over charged system
  • Poor airflow
  • Undercharged system

A properly maintained AC system should never have mold growth.

If you would like to learn how to become an AC Technician or have any questions please call or email us.

About The Author

Ron Walker

After retiring from the U.S. Marines and achieving his B.S. degree, Ron Walker entered the HVAC field. He has been an HVAC technician, service manager, and business owner. Working as a service manager, he spent many years training HVAC technicians to be more technically competent and really understand their trade. His passion for teaching and helping others resulted in the creation of HVAC Training Solutions, LLC.