Furnace Destroyer #4 – The AC Coil

Heat Exchanger Destroyer #4 – The Air Conditioner Evaporator Coil

In the operation of HVAC equipment there are relationships between components that are too often overlooked. What does the furnace heat exchanger have to do with an evaporator coil (A-Coil) from the air conditioning system?

Air flow – is the common link!

Over a period of several years, the evaporator coil of an air conditioning system will collect dust, dirt and debris. It’s inevitable that the coil will need service at some point. Imagine 400 cubic feet of air per minute passing through the coil above your furnace. Multiply that by 3 or 4 tons of cooling and that number quickly becomes 1200 to 1600 cubic feet of air per minute. It’s not a matter of if the coil will get dirty – it’s a matter of when will it need a good cleaning?

Not all technicians inspect the evaporator call on every service call. The best practice is to inspect all heat exchangers and at the same time inspect the evaporator coil for dirt and debris. The evaporator is located directly in the same air steam as the heat exchanger. If the evaporator coil becomes dirty the airflow across the heat exchanger will be reduced resulting in additional and unnecessary stress to the furnace. This is another relationship that will destroy a furnace’s heat exchanger.

In our business – we call this; The Heat Exchanger Destroyer #4

Here are some technician tips and musts when having a furnace or air conditioner serviced:

  1. Inspect the entire heat exchanger
  2. Inspect the evaporator coil
  3. Check the filter

Tips for homeowners:

  1. Hire qualified, educated and knowledgeable technicians
  2. Ask questions
  3. Ask the technician to show you the evaporator coil or heat exchanger
  4. Have your system service annually and in some climates twice per year
  5. Avoid the advertising that offers a too good to be true deal – like the cheap $39, $49, $59 or up to $99 tune ups. These usually are too good to be true resulting in important steps being skipped.
  6. Get to know the company that you are working with. Visit their websites and call their owners. Build a relationship of trust.


I know that this picture is a little extreme. However, it really came from a home in Milwaukee, Wisconsin. Realize that even a little dirt or debris on the surface of an evaporator coil can decrease airflow and result in higher utility bills and lower performance.


The worse A coil that I've ever seen. PLUGGED

The worse A coil that I’ve ever seen. PLUGGED

Taken directly from the Mr. Holland’s Heating and Air Conditioning best practices library.


Some questions and comments from homeowners:

“Can I clean my own evaporator coil?”   –  Yes. However, it’s unlikely that you will have the necessary tools to perform an airflow adjustment and refrigerant charge analysis. After any coil is cleaned your air conditioning system will require airflow adjustments. Plus, you will need to know how to access the coil without damaging refrigerant lines and cracking the plastic drain pan.

“My air conditioning guy said that I only have to check this if my unit is not working (my coil is in my attic).”  FALSE. Get a new air conditioning guy! Typical HVAC companies rarely check the evaporator coil on maintenance visits. This is a MUST on every tune up!