Photograph of a blocked corroded air conditioning evaporator coilAir Conditioning & Heat Pump Air Handler Cooling Coil Blockage

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Cooling coil blockage by debris, damage, or ice - diagnosis & repair:

This air conditioning repair article discusses the problem of dirt or debris blockage of the air conditioning system's cooling coil or evaporator coil in an air conditioning system air handler, how the dirt gets there, what problems it causes, how to clean a cooling coil (or evaporator coil), and how to prevent future dirt on the coil.

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Blocked Cooling Coil: Air Conditioner Evaporator Coil Blocked by Debris

Photograph of a dirt blocked air conditioning evaporator coil

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?

[Click to enlarge any image]

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.

For A/C or heat pump cooling coil blockage problems, also see  DIRTY COIL CLEANING PROCEDURES and  FROST BUILD-UP on AIR CONDITIONER COILS . If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building.

Photograph of a dirt blocked air conditioning evaporator coil

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.

How do we clean a dirty air conditioner or heat pump cooling coil or evaporator coil? 

What Else Causes a Blocked Air Conditioning Evaporator Coil or Reduced Air-flow Across the Coil?

Dirty air filter: can be mistaken for a blocked cooling coil. Always check your air filter first. Replace it if it's clogged and dirty and check the filter regularly.

Air Conditioner Evaporator Coil Frost or Ice Formation: When the coil becomes sufficiently blocked with debris as to slow down the air flow enough, the coil may actually become so cold that the condensate forming on its surface freezes, completely blocking the coil.

That's because the rate of release of refrigerant into the evaporator coil was designed with an assumption of a sufficient volume of air moving across the coil to keep it from becoming too cold.

When the surface temperature of an air conditioning cooling coil drops below 32 degF or 0 degC, condensate forming on the coil surface begins to freeze, leading to sometimes some pretty weird behavior of the cooling system as we discuss
at FROST BUILD-UP on AIR CONDITIONER COILS where we explain that there can be more than one reason that a cooling coil ices-up but none of those conditions is desirable.

Damaged air conditioner coil fins: can occur on both the evaporator (cooling) coil and the outside condensing coil.

See CONDENSING COIL REPAIR REPLACE for discussion of repairing bent or damaged coil fins. Only in extreme cases will fin damage be so severe that air flow across the cooling coil is severely blocked - enough to cause loss of function or coil icing.

Dirty air handler blower fan: see AIR HANDLER / BLOWER UNITS and its section titled DIRTY A/C BLOWERS This article describes the very significant reduction in airflow across a cooling coil that can occur if the squirrel cage fan blades are dirty on the blower fan in the air handler. A dirty blower fan can be the cause of reduced airflow across the cooling coil and can even lead to coil icing.

Air leaks or unnoticed duct openings: in the duct system can interfere with proper airflow through the duct system, reducing air delivery into the building, and can be mistaken for a blocked or dirty cooling coil. Details are

Air Conditioner or Heat Pump Cooling Coil Articles


Continue reading at DIRTY COIL CLEANING PROCEDURES or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.



Or see COOLING / EVAPORATOR COIL REPAIR to diagnose cooling coil leaks or to replace a corroded, leaking coil

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DIRTY COOLING COIL / EVAPORATOR COIL at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


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