A small diameter equalizer tube on a rack is found weeping refrigerant exactly where it crosses a steel frame member, with the copper worn bright and thin at that point. What has caused the leak?
Correct Answer
B) Vibration wearing the tube wall away where it rubs against the steel
A compressor running on a rack shakes everything attached to it. Where a small tube touches a rigid frame member the two surfaces work against each other thousands of times an hour, and the copper, being softer, gives up material until the wall is thin enough to open. The bright polished patch is the signature. The repair is to fix the leak and then isolate the tube from the frame with a grommet or a clamp so the rubbing cannot start again.
Why This Is the Correct Answer
Vibration from the compressor causes the tube to move against the steel frame, and the softer copper wears away at the contact point. The bright, thinned area is exactly what abrasion leaves behind. Repairing the tube without separating it from the frame guarantees the same failure again, so the fix includes cushioning or reclamping the line.
Why the Other Options Are Wrong
Option A: Galvanic action between the copper tube and the steel frame member
Galvanic corrosion needs an electrolyte bridging the two metals and leaves a rough corroded surface, not a bright polished wear patch.
Option C: Heat conducted from the frame gradually annealing the copper wall
A frame member sits at the same temperature as everything around it. Nothing on a rack conducts enough heat into a tube to anneal it through.
Option D: Overpressure stretching the tube where the frame restrained it
Overpressure would bulge or split the tube along its weakest section, and it would not selectively thin the wall at a single contact point.
Memory Technique
Copper against steel, all day, every day. Steel always wins.
Reference Hint
Vibration rub-through occurs where refrigerant tubing contacts rigid structure; the repair includes isolating the tube.
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