Why do we clean the HVAC evaporator or cooling coil

Dirt and debris accumulating on an air conditioner or heat pump coil block airflow across the coil, increasing the cost of heating or cooling the building. In severe cases cooling or condensing coils can become so blocked that air flow is seriously reduced, possibly also leading to:

• an evaporator or cooling coil icing problem indoors
• an overheated, damaged compressor outdoors
• simply a loss of cooling capacity of the system.

In addition, a blocked evaporator coil can cause the HVAC compressor to run at higher than normal temperatures – a condition that over time can break down lubricants circulating inside the system, thus shortening the life of the compressor motor itself.

Air Conditioner Evaporator Coil Blocked by Debris

Ice on the cooling coil is not the only (nor even the most common) cause of blocked air flow in an air conditioner. This photograph shows how easily debris can stick to and clog the inlet side of the cooling coil in an air conditioning system. This evaporator coil was nearly totally blocked with dust and debris. How does this happen?

There was no air filter installed in the system. Ordinary house dust is comprised largely of fabric fibers and skin cells.

These and other debris in building dust such as soot and organic particles like pollen and mold spores all join to form a gray mat on the fins of the cooling coil in an air handler.

Debris sticks particularly quickly to this surface because of the combination of close spacing of the cooling fins (about 1/16″ apart) and the fact that condensate forming on the coil keeps the surface damp.

Here is a close up photograph showing how fibers in building dust readily cross the blades of the cooling coil and how the fibers themselves then collect smaller particles to rapidly block air flow across the coil. The same principles that make an air filter work can also clog the cooling coil of an air conditioning system.

As a cooling coil (or evaporator coil) in an air conditioner becomes blocked with dust and debris the air flow across the coil is reduced.

This reduced air flow (in cubic feet per minute or CFM) across the coil means that the cooling capability of the whole air conditioning system is reduced.

Cleaning Indoor Coil

If the coil is contaminated with a light dust or dirt not adhered to the fins, blowing low pressure compressed air across the fins or the use of a soft bristle brush may be sufficient.  Applying a plain water or mild detergent solution to the surface, allowing it to sit for a short time then rinsing is employed in some cases.  More aggressive deposits call for the use of stronger cleaning solutions or solvents as required.

As shown in previous photos dirt/debris gets embedded in the coil between the fins (impacted).  A simple coil cleaning of the surface will not be sufficient to remove this debris.  The use of a foaming agent (cleaner) is required.  The Home Improvement stores carry a cleaner that will suffice for slightly impacted coils but for more heavily impacted coils – the ones that give you trouble by icing or noticeable performance issues -  require a stronger professional cleaner.

If possible and practical the coil should be removed from the system in order to access all angles required for cleaning.  This process requires a professional with EPA certification to handle refrigerants. The pressure is relieved from the system by pumping the system down or recovering the refrigerant.  After the refrigerant and pressure is at 0 psig in the coil the coil is removed from the system and taken to a safe environment with water access for cleaning.  The cleaner is then sprayed on the coil and allowed to penetrate the fins to lift the dirt out. Water is then back-washed through the fins to flush out the impacted debris.  This process should be repeated until the fins are clear of the debris  The coil is then placed back in position.  The copper tubing is then brazed and leak checked.  The system is dehydrated and refrigerant is returned to the system.  It is a time consuming process and 2-3 hours should be allowed for the process.

Cleaning the coil in place can be unwieldy.  However, there are times that coil removal isn’t practical or possible.  This could be due to many reasons including unit location restrictions; the unit configuration or coil size.  In these cases a water source must be available.  Additionally, understanding the use of chemicals and water, a means to remove the muck and prevent from causing damage.