A leak on a household refrigerator has been traced to the aluminum evaporator tubing, and the technician's kit holds only the silver bearing alloy used for copper joints. What does that combination mean for the repair?
Correct Answer
B) The alloy will not join aluminum, so the coil is replaced or the repair done another way
Silver bearing brazing alloys are formulated for copper, brass and steel. Aluminum has a much lower melting point than those alloys need, and its surface oxide reforms instantly, so a technician who tries anyway melts the tubing before anything flows. Aluminum joints need aluminum specific rods and flux with a working temperature below the base metal, or a mechanical repair method made for the purpose. Brazing copper over aluminum fails for the same reason and adds a dissimilar metal joint that corrodes. Very often the practical answer on a small appliance is replacing the coil.
Why This Is the Correct Answer
The alloy's working temperature is above the melting point of aluminum, so it cannot form a joint on aluminum tubing under any amount of cleaning or flux. Aluminum work needs low temperature aluminum rod with matched flux, careful heat control, and often a backing repair sleeve made for the alloy. Where the leak is in a formed evaporator, replacing the coil is frequently the only realistic route.
Why the Other Options Are Wrong
Option A: The joint can be made if the aluminum is cleaned to bright metal and fluxed heavily
Cleaning and flux address surface oxide. They do nothing about an alloy whose working temperature is above the melting point of the base metal.
Option C: The alloy works on aluminum at a lower torch temperature than it needs on copper
Working temperature is a property of the filler alloy, not of the metal underneath. The same rod needs the same heat wherever it is used.
Option D: The leak can be sealed by brazing a copper sleeve over the aluminum tubing instead
A copper sleeve cannot be brazed to aluminum for the same reason, and joining the two metals directly sets up galvanic corrosion at the joint.
Memory Technique
The rod melts hotter than the tube. There is no technique that fixes that.
Reference Hint
Silver bearing brazing alloys are for copper, brass and steel. Aluminum requires aluminum specific rod and flux, or replacement of the part.
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