313D System Installation and Brazing 3 — Questions and Answers
Question 1: When using an oxyacetylene torch for brazing refrigerant lines, the flame should be adjusted to a:
- Carburizing (reducing) flame
- Neutral flame (Correct answer)
- Oxidizing flame
- Turbulent blue flame
Correct answer: Neutral flame
A neutral flame provides the correct heat balance for brazing copper without introducing excess oxygen or carbon to the joint.
Question 2: What is the maximum recommended length of an unsupported horizontal refrigerant line run before a support hanger is required?
- 3 feet
- 5 feet (Correct answer)
- 8 feet
- 12 feet
Correct answer: 5 feet
Refrigerant lines should be supported at least every 5 feet horizontally to prevent sagging, vibration damage, and stress on joints.
Question 3: Before making a brazed joint on an existing system, the technician must first:
- Pressurize the system with nitrogen
- Recover all refrigerant from the system (Correct answer)
- Flush the lines with R-11
- Purge lines with CO2
Correct answer: Recover all refrigerant from the system
Federal regulations require all refrigerant to be recovered before any brazing or repair that opens the refrigerant circuit.
Question 4: Which type of copper tubing is approved for use in refrigerant line sets for residential AC systems?
- Type M hard-drawn copper
- ACR (Air Conditioning and Refrigeration) grade copper (Correct answer)
- Type L soft copper plumbing tube
- Galvanized steel tubing
Correct answer: ACR (Air Conditioning and Refrigeration) grade copper
ACR-grade copper tubing is cleaned, dehydrated, and capped at the factory, making it suitable for refrigerant service.
Question 5: When routing refrigerant lines through a wall or floor, the technician should:
- Leave lines bare to allow visual inspection
- Install a protective sleeve or grommet to prevent abrasion (Correct answer)
- Wrap lines tightly with duct tape only
- Solder lines to the framing for stability
Correct answer: Install a protective sleeve or grommet to prevent abrasion
A sleeve or grommet protects the refrigerant lines from abrasion against sharp edges, which can cause premature leaks.
Question 6: The suction line in a residential split system is typically insulated to:
- Prevent refrigerant from overheating
- Prevent condensation and maintain superheat entering the compressor (Correct answer)
- Reduce refrigerant velocity
- Lower the discharge pressure
Correct answer: Prevent condensation and maintain superheat entering the compressor
Insulating the suction line prevents heat gain from the ambient air, which could cause excessive superheat and reduce system efficiency.
Question 7: After completing all brazed connections on a new installation, the next step before charging with refrigerant should be:
- Pull a vacuum immediately to 500 microns
- Pressure-test the system with dry nitrogen and check for leaks (Correct answer)
- Add refrigerant oil and then charge
- Run the system briefly to seat compressor valves
Correct answer: Pressure-test the system with dry nitrogen and check for leaks
Pressure-testing with dry nitrogen to the manufacturer's specified test pressure and leak-checking all joints is required before evacuation and charging.
313D System Installation and Brazing 3
When using an oxyacetylene torch for brazing refrigerant lines, the flame should be adjusted to a: