Photograph of attic air conditioning air handler, condensate drips on floor Effects of Cooling Coil or Evaporator Coil Ice-up or Frost Over
on Air Conditioners or Heat Pumps

  • FROST / ICE IMPACT on A/C - CONTENTS: what are the symptoms of evaporator coil frost or ice blockage and what problems does this ice or frost blockage cause for air conditioners or heat pumps?
  • POST a QUESTION or READ FAQs about the causes, effects, and cures of icing or frost formation on the air conditioner or heat pump cooling coil

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Effects on A/C or heat pump system operation due to cooling coil ice & frost formation. This air conditioning repair article series discusses evaporator coil icing: the problems of ice and frost formation in air conditioning system air handler units, blower units, or AHU's, duct work, or other air conditioning system components. A freezing or frosted A/C coil blocks air flow and leads to loss of cooling.

The air conditioning system evaporator coil and problems of frost build-up on the air conditioning coil are explained and diagnosed here Our page top photograph of a thoroughly ice-blocked air conditioner evaporator coil was contributed by a reader who described: "I cleaned the coils & installed a new filter - obviously I have a low refrigerant problem. This is an 11 year old furnace/air handler with no history of other problems, but low on Freon."

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Effects of Coil Frost & Ice in the HVAC System

Photograph of attic air conditioning air handler, condensate drips on floorWhat Happens to the Ability of the Cooling System to Cool the Air When an Evaporator Coil Ices Up?

When the cooling coil has a nice thick ice build-up on its surface there will be no cool air produced by the air conditioning system at all. The fan runs, outside compressor/condenser run, but little or no air moves through the duct system. The page top photograph shows icing on the cooling coil and refrigerant lines exiting the coil inside air handler close to the evaporator coil even.

You might see ice formation on the suction line just outside of your air handler even though you cannot see the evaporator coil itself - on most residential air conditioning systems, the surfaces of the cooling coil are not readily accessible by the homeowner. But if you don't see ice on the suction line, ice could still be present on and blocking air flow through the cooling coil.

The cooling coil, or evaporator coil is visible if the air handler is opened on some air conditioner units. At other installations the cooling coil is completely covered and can't be seen at its location (say on a retrofit installation atop an existing hot air furnace) unless an inspection opening has been made (by cutting the steel and installing an access panel cover), or unless there is an opening that was made previously to install a humidifier in the same plenum chamber.

When an air conditioning system with a frost-blocked coil is turned off and allowed to warm up the ice on the coil melts and spills into the internal condensate collector tray in the air handler. Then when the air conditioner is re-started it may for a while produce cool air before becoming ice blocked again. If an air conditioning system behaves in this way coil icing is a possible explanation.

Frost build-up indicates an air flow or refrigerant problem. A blocked coil (by dirt) or a blower fan which has lost its ability to move air (such as a dirty squirrel cage fan) will reduce air movement across the coil and lead to frost build up there. We suspect this is the more common cause of this defect. We discuss the problem of dirt on the cooling coil slowing air flow and leading to ice-build-up at DIRTY COOLING COIL.

[Photograph of ice formation at the suction line of an air conditioning compressor/condenser unit (and some odd insulation there) courtesy of Mark Cramer a past president of ASHI and a Florida home inspector.]


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