There are two issues that we can identify from the pictures
1. There is formicary corrosion (ants nest corrosion) occurring on the copper tubes giving you leaks.
This can be from two specific things
- From an acid environment created by the food that the evaporator is cooling. Acetic Acid
- From a harsh cleaning chemical that this customer has used to clean the coils. (probable BLEACH)
2. There is damage on other parts of the UNIT from an Alkaline cleaner which has not been rinsed off.
This customer may have damaged the coil using a aggressive cleaning chemical and then not washing off. Maybe BLEACH Conc.
Recommendation
1) All coils for this customer require a single dip and then separate overspray of the copper return bends and surrounding area.
The coil is baked very well to crosslink.
2) Should only clean with fresh water.