Photograph of attic air conditioning air handler, condensate drips on floor Refrigerant Piping Ice or Frost Diagnosis & Repair
in Air Conditioners or Heat Pumps
     


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Cooling coil ice & frost formation diagnosis & cure; refrigerant line frost cause & remedy.

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. If you don't see information you want, ask us for it using the comments box on this page.

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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Why Frost or Ice May Appear on an Air Conditioning Refrigerant Suction Line

Photograph of ice formation on the suction line of an
air conditioner compressor/condenser unit in Florida -- Mark Cramer The ice formed here is at the low pressure inlet to an air conditioning compressor condenser unit. Similar ice may form at the evaporator coil (also called the cooling coil) or at the refrigerant suction line on the cooling coil at other end of the air conditioning system, as you can see in our iced-up air conditioning cooling coil photograph at the top of this page. [More photographs wanted].

Frost and ice can even form inside air conditioning duct work, leading to troublesome leaks into the building. This article explains locations and causes of condensate, frost or ice formation in air conditioning systems, air handlers, compressor/condensers, refrigerant lines, and in air ducts.

Several reasons can cause frost or ice formation not only on the cooling coil, but on the refrigerant suction lines at the equipment as well:

  • Blocked air flow across the cooling coil, for example from a dirty air filter, collapsed duct insulation, crimped flex-duct, or similar problem.
  • Refrigerant charge level: Improper refrigerant charge (too low a charge of refrigerant in the A/C system can, for a while, lead to too-low temperatures in the coil which will then cause frost or ice build-up on the suction line.

    Ultimately however, when there is simply little or no refrigerant left in the cooling system, temperature at the cooling coil will climb back up, the frost will disappear, and you'll no longer have any cooling at all. In air conditioning service schools the instructor may demonstrate this effect by dynamically adjusting the amount of refrigerant in the cooling system as students watch the frost line extend down the suction line, then crawl back up to near the end of the cooling coil as the proper refrigerant charge amount is reached.

    Alternatively, on some cooling systems too much refrigerant can cause liquid refrigerant to flow past the cooling coil into the suction line,also causing icing.
  • TEV/Cap Tube: a malfunctioning refrigerant metering device like a bad thermal expansion valve (TEV). Conversely, a bad capillary tube (a more rudimentary refrigerant metering device found on refrigerators, dehumidifiers, and window air conditioners) won't fail by passing too much refrigerant but it might fail to pass any refrigerant at all if it becomes blocked by debris or by a slug of oil in the system.
  • Defrost control: A malfunctioning auto-defrost control or bad defrost timer control (less common on residential air conditioning systems)

Technical Note on Refrigerant Piping, HVAC Design and Heat Exchange Between the Low Pressure & High Pressure Refrigerant Lines: an HVAC economizer detail using refrigerant line brazing or soldering together

In some air conditioners or heat pumps at the point where the low-side suction line enters the compressor condenser unit the low-temperature (heat laden) vapor line (suction line) is soldered or brazed right next to and touching the high-temperature, high-pressure liquid refrigerant line.

The purpose of this refrigerant piping detail is to act as a heat exchanger, to reduce the temperature of the liquid refrigerant that is going to enter the metering device (TEV or cap tube), gaining some benefit to system operation.

Details about soldering or brazing the two refrigerant lines in direct contact are discussed at REFRIGERANT PIPING INSTALLATION - at Technical Note on Refrigerant Piping: HVAC economizer detail or select a topic from the More Reading links shown below.

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