313D System Installation and Brazing 2 — Questions and Answers
Question 1: When brazing copper refrigerant lines, what minimum silver content is required for the brazing alloy used in most residential AC applications?
- 2% silver
- 5% silver
- 15% silver (Correct answer)
- 45% silver
Correct answer: 15% silver
Brazing alloys with at least 15% silver content are typically required for refrigerant line brazing to ensure strong, leak-free joints.
Question 2: Nitrogen should be flowing through refrigerant lines during brazing primarily to:
- Cool the joint faster
- Prevent internal oxidation and scale formation (Correct answer)
- Increase brazing temperature
- Reduce silver content needed
Correct answer: Prevent internal oxidation and scale formation
Flowing dry nitrogen through the tubing during brazing displaces oxygen and prevents the formation of copper oxide scale inside the lines.
Question 3: What is the correct sequence for making a brazed refrigerant line connection?
- Heat joint, insert tube, apply flux, braze
- Insert tube, apply flux, heat joint to brazing temp, apply filler (Correct answer)
- Apply filler, heat joint, insert tube, cool quickly
- Insert tube, heat joint, apply filler, apply flux
Correct answer: Insert tube, apply flux, heat joint to brazing temp, apply filler
The proper sequence is to insert the tube fully, apply flux if needed, heat the joint evenly to brazing temperature, then apply the filler rod at the joint.
Question 4: When installing a split-system air conditioner, the indoor unit's condensate drain line should be pitched at a minimum slope of:
- 1/8 inch per foot
- 1/4 inch per foot (Correct answer)
- 1/2 inch per foot
- 1 inch per foot
Correct answer: 1/4 inch per foot
A minimum slope of 1/4 inch per foot ensures proper gravity drainage of condensate without pooling.
Question 5: Which tool is used to properly size copper tubing for flare or swage connections during installation?
- Pipe reamer
- Tubing cutter and deburring tool (Correct answer)
- Swage block only
- Pipe bender
Correct answer: Tubing cutter and deburring tool
A tubing cutter makes a clean, square cut and the deburring tool removes the inner burr to ensure a leak-free connection.
Question 6: During a residential AC installation, the outdoor condenser unit should be elevated above grade to:
- Reduce refrigerant pressure drop
- Prevent flooding and allow air circulation beneath the unit (Correct answer)
- Lower the center of gravity for stability
- Reduce compressor vibration noise
Correct answer: Prevent flooding and allow air circulation beneath the unit
Elevating the condenser on a pad protects it from standing water and allows proper airflow under the unit.
Question 7: What is the purpose of adding a trap in the suction line when the evaporator coil is located above the condensing unit?
- To reduce refrigerant velocity
- To prevent oil from draining back to the compressor during the off cycle (Correct answer)
- To increase suction pressure
- To trap liquid refrigerant before the compressor
Correct answer: To prevent oil from draining back to the compressor during the off cycle
A suction line trap prevents oil from draining back into the compressor crankcase when the system is off, which could cause liquid slugging on startup.
