There is a phenomena in refrigeration called stress corrosion. Evaporator copper u-bends experience this phenomena in an acidic enviornment
Pinhole leaks develop in the outer portion (area of greatest stress) of the u-bends, when subjected to an acid enviorment.
The evaporator, on small deli sandwich makers and reach-in coolers, where pickles are kept, is subjected to this enviornment when the sandwich makers or other pickle users dont cover the pans with pickles or pickled peppers or anything else acidic like lemon juice.
The acid vapor from the vinegar, etc will cause stress corrosion --- it may take a year or several, for the copper to erode to the point where leaks develop . I have seen this phenomena on numerous occasions. The pinholes can be filled if not too bad-- I use soft solder with rosin core instead of silphos brazing rod as the copper is very weak at this point and the heat required for silphosing can cause bigger leaks-- but the best fix is to replace the evaporator and educate the user.
I would suggest looking at soil pH for a strong acid condition.
If the copper used is hard drawn, which I suspect it is, there may be enough stress in the copper to allow stress corrosion to occur if the soil conditions are strongly acidic.
I believe there are inexpensive soil ammendments that might bring up the pH. I would ask a good landscape maintenance company or geologist to see what they suggest for eliminating an acid soil condition. I think there are soil test kits at many gardent centers--- if the pH is much below 7, say 4 or 5, that might be the cause.
It may also be that the copper used in that housing complex came from a faulty batch to begin with--try to get a sample of the same material from inside the house and then send it to a metalurgist for grain structure analysis and susceptibility to stress corrosion
Good luck
Bill Bill
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