ASTG12LVCB - Discharge Temperature Error / Evaporator Corrosion

This article summarises a quality investigation into an ASTG12LVCB indoor unit that developed a discharge temperature error after approximately three years of operation. The investigation identified refrigerant leakage from the evaporator caused by external corrosion.

Key finding: The evaporator leak was traced to pinhole corrosion originating from the outside of the copper tube. The corrosion pattern was described as ant's nest-like corrosion.

Applies To

ProductASTG12LVCB
Reported unit referenceE005389
Reported faultDischarge temperature error
Approximate age at failure3 years

Problem Detail

  • The unit developed a discharge temperature error after approximately three years in service.
  • The attending technician found evidence of oil leakage around the indoor unit heat exchanger and drain pan.
  • The returned sample was subjected to a sink / leak test as part of the factory investigation.

Analysis Result

During testing of the returned indoor unit, a refrigerant leak was identified from a pinhole in the evaporator.

Factory finding: The leak was caused by corrosion progressing from the outside surface of the evaporator tube.

The appearance of the corrosion was described in the quality report as ant's nest-like corrosion.

Suspected Cause

The factory assessment was that the corrosion had progressed from the outside of the copper tube due to factors associated with the operating environment.

Important: The report does not identify one specific environmental contaminant or site condition. It only concludes that external environmental factors were considered the likely driver of the corrosion.

Factory Countermeasure

To improve resistance to corrosion caused by external environmental factors, the factory planned to change the evaporator piping material to oxygen-free copper.

  • Existing tube material was to be reviewed and replaced with oxygen-free copper.
  • The purpose of the material change was to suppress the occurrence of this type of corrosion.
  • The source quality report did not provide a confirmed implementation date.

Service Guidance

  • If an ASTG12LVCB presents with a discharge temperature error, check the refrigeration system for evidence of refrigerant loss.
  • Inspect the indoor heat exchanger and drain pan area for oil staining, which may indicate an evaporator leak.
  • If leakage is suspected, carry out an appropriate leak test of the evaporator.
  • Where pinhole leakage is confirmed, inspect the tube surface for signs of corrosion originating externally.
  • The factory report supports evaporator corrosion as a possible cause in this model, but does not state that every discharge temperature error is caused by this issue.