Sketch of a cooling coil (C) Carson Dunlop Associates Air Conditioning & Heat Pump Cooling Coil Diagnosis & Repair

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Air conditioning, heat pump or refrigerator cooling coil (evaporator coil) diagnosis & repair procedures:

How to diagnose problems such as leaks, corrosion, or other damage that requires replacement of the air conditioning or heat pump cooling coil (evaporator coil in the air handler).

This article series discusses the diagnosis and repair of cooling coil or evaporator coil problems that occur in the air conditioning or heat pump air handler unit such as frost or icing, dirt, blockage, refrigerant leaks, or improper sizing.

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Guide to Evaluating Evaporator Coil or Condensing Coil Refrigerant Leaks and Deciding to Repair or Replace a Coil

Sketch of an air conditioner or heat pump evaporator coil (C) Carson Dunlop Associates

Article Contents

[Click to enlarge any image]

Evaporator coil or cooling leaks or holes: if an evaporator coil is leaking (or also if the condensing coil is leaking) you'll find out pretty quickly as refrigerant will be lost and the cooling system will stop providing cool air.

You'll need expert diagnosis by an HVAC service technician. Sketches of the evaporator coil or cooling coil shown at left and at page top were provided courtesy of Carson Dunlop Associates a Toronto home inspection, engineering, and education firm.

Replacement of the cooling coil (or condensing coil) is more often going to be recommended by your HVAC technician because of these difficulties.

Guide to Repairs of an Air Conditioning or Heat Pump Evaporator Coil or Condensing Coil

Sketch of a cooling coil (C) Carson Dunlop Associates

  1. Review the coil inspection, diagnosis, and repair tips

    We find that the terms "cooling coil" and "evaporator coil" are used as synonyms in most cases.

    Sketch at left courtesy of Carson Dunlop Associates. [Click to enlarge any image]

    Even if the cooling or condensing coil has a repairable leak, if the coil is badly damaged such as having all crushed fins, it may be best to replace it.

    Damaged cooling / evaporator coil fins over more than 10% of the coil surface, blocking air flow may be a reason to replace the coil.
  2. If the cooling coil or condensing coil is in good physical condition but it's dirty, it needs to be cleaned before it can be repaired. Spray-on coil cleaners are used by lots of HVAC technicians.

    If the coil is dirty with moldy dust and debris and especially if the building is occupied by people at extra health risk, we don't like to see an indoor coil cleaned by blowing it off with compressed air, as you're simply sending all of this moldy junk into the building.
    See DIRTY COOLING COIL / EVAPORATOR COIL and see Mold Growth in Air Handlers.

    You may also want to check out Leaks, Rodents In Air Handlers.
  3. Next check the cooling coil or evaporator coil for visual evidence of refrigerant leaks. Visual evidence of a refrigerant leak on a coil may include stains from refrigerant oil left at the point of leakage.
  4. When the one or more places where the cooling coil or evaporator coil is leaking refrigerant gas have been found, it's time to decide if we can perform a solder repair of if the coil has to be replaced. We offer some suggestions
    at Guide to Evaluating Evaporator Coil or Condensing Coil Refrigerant Leaks

Decision to Replace an HVAC Cooling Coil or Evaporator Coil & Replacement Costs

Photograph of attic air conditioning air handler, condensate drips on floorIf the decision is to replace the cooling coil or the evaporator coil, be sure that the new coil is the proper size and shape to match the condenser or evaporator unit itself.

[Click to enlarge any image]

Reader Question: should I try to fix a leaky refrigeration coil on my air conditioner?

3/27/14 Mike said:

My air conditioner is 8 years old. The system is leaking refrigerant at a slow level and the hole is midway through coil. Should I try to fix the coil or opt for a new unit?


Some AC coils can be repaired using epoxy but I am not optimistic about this approach. Here are some considerations:

If the coil leak was caused by an accident, like a mechanical puncture, repairing it might yield a durable remaining life for the system provided we don't contaminate (or contaminate and fail to clean) the refrigerant piping system in the process.

If the AC coil leak was caused by vibration and rubbing or by corrosion I fear that fixing the leak in one place is a band-aid repair that won't give a durable repair since other leaks are coming soon. It's the beginning of the end.

If the HVAC system is relatively new so that it uses modern contemporary refrigerants, then replacing the coil is a plausible repair and the recommended one. The system will have to be evacuated, cleaned, new refrigerant installed along with appropriate refrigerant dryer/filters.

If the HVAC system were old enough (probably not your case) that it still uses R22, repair people either take another band-aid approach by replacing the ruined coil with an R-22-rated coil and R22 refrigerant (no longer a proper repair as this refrigerant has been phased out of use) OR the technician may be tempted to install a new coil rated to use a new refrigerant.

But that last approach leads to more costs: a coil mismatched to the rest of the equipment will operate very poorly, as demonstrated by

and when we change refrigerant we may need to change additional controls (TEVs for example) increasing the job cost until it begins to look as if a complete outdoor compressor/condenser unit replacement or even a whole system replacement would have been a smarter change.

For an example of coil replacement costs see our condensing coil replacement discussion

Install a Refrigerant Drier / Debris Filter after replacing the evaporator coil

Watch out: good practice following work on refrigerant piping systems or system evacuation and recharging within refrigerant includes the installation of a debris filter and refrigerant drier device.

Details are

Air Conditioner or Heat Pump Cooling Coil Articles


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