CRST Piping, Tubing & Brazing Techniques 3

Question 1

At approximately what temperature range does silver-phosphorus-copper (BCuP-5) brazing alloy flow and fill refrigeration copper joints?

Accepted Answer

1,200–1,500°F (649–816°C)

Answer

BCuP-5 has a solidus near 1,190°F and liquidus near 1,475°F, placing its working brazing range at approximately 1,200–1,500°F—well above soft-solder temperatures but below copper's melting point.

Question 2

After completing a brazed joint in a refrigeration line, what is the correct method for allowing the joint to cool?

Accepted Answer

Allow the joint to air cool naturally without applying water or forced cooling

Answer

Brazed joints must air cool naturally because quenching with water causes thermal shock that can crack the braze alloy, stress the base metal, or weaken the joint.

Question 3

When brazing copper tubing to a brass fitting (such as a service valve body), what additional step is required that is NOT needed for copper-to-copper joints?

Accepted Answer

Apply brazing flux to the joint before heating, because BCuP alloys are not self-fluxing on brass

Answer

BCuP alloys are self-fluxing only on copper-to-copper joints; when brazing copper to brass, bronze, or steel, an appropriate brazing flux must be applied to prevent oxide formation and ensure proper alloy flow.

Question 4

What is the correct tool and technique for cutting ACR copper tubing to achieve a clean, square, burr-minimized cut?

Accepted Answer

Tubing cutter rotated around the circumference with gradually increasing blade pressure

Answer

A tubing cutter produces a clean, square cut perpendicular to the tube axis and is the standard method for copper ACR tubing, minimizing deformation and maintaining the tube's roundness.

Question 5

Immediately after cutting copper ACR tubing with a wheel-type tubing cutter, what mandatory step must be performed before brazing?

Accepted Answer

Ream the inside of the cut end to remove the inward burr created by the cutting wheel

Answer

The cutting wheel displaces metal inward, leaving a burr that reduces the inside diameter; reaming removes this burr to restore full flow area and prevent debris from entering the system.

(CRST) Certified Refrigeration Service Technician Practice Test

(CRST) Certified Refrigeration Service Technician Practice Test

CRST Piping, Tubing & Brazing Techniques 3