313A Piping, Brazing & Leak Detection 2 — Questions and Answers
Question 1: Which refrigerant leak detection method offers the highest sensitivity, capable of detecting leaks as small as 0.1 oz per year?
- Bubble solution (soap) test
- UV fluorescent dye and black light
- Electronic refrigerant leak detector (Correct answer)
- Nitrogen standing pressure test
Correct answer: Electronic refrigerant leak detector
Electronic leak detectors (heated diode, infrared, or heated pentode types) are capable of detecting trace levels of refrigerant far below the threshold of bubble or UV dye methods.
Question 2: Under Canadian federal refrigerant regulations, technicians must repair leaks in systems with a refrigerant charge above what threshold within 30 days of detection?
- Any system regardless of charge size
- Systems with a charge above 3 kg (Correct answer)
- Systems with a charge above 100 kg
- Only R-22 and other HCFC systems
Correct answer: Systems with a charge above 3 kg
Under Canada's Ozone-depleting Substances and Halocarbon Alternatives Regulations (CEPA), systems containing more than 3 kg of refrigerant must have detected leaks repaired within 30 days.
Question 3: When pressure testing a refrigerant system, dry nitrogen is preferred over refrigerant because:
- Nitrogen is less expensive and always available at the jobsite
- Nitrogen is inert, non-toxic, non-flammable, and leaves no residue in the system (Correct answer)
- Nitrogen can reach higher test pressures than most refrigerants
- Nitrogen dissolves in refrigeration oil, making leak paths more visible
Correct answer: Nitrogen is inert, non-toxic, non-flammable, and leaves no residue in the system
Dry nitrogen is the preferred test medium because it is inert, poses no environmental risk, carries no oil contamination risk, and does not condense at test temperatures.
Question 4: UV dye leak detection requires which additional piece of equipment to be effective?
- An infrared thermal camera
- A UV (black light) lamp and UV-filtering safety glasses (Correct answer)
- A digital manifold gauge set to confirm suction side leaks
- A refrigerant identifier to confirm dye compatibility
Correct answer: A UV (black light) lamp and UV-filtering safety glasses
UV fluorescent dye only becomes visible when illuminated by an ultraviolet (black light) lamp, and UV-filtering glasses enhance contrast to reveal even faint traces of dye.
Question 5: A nitrogen standing pressure test is held at 200 psig. After 60 minutes the gauge reads 192 psig with no change in ambient temperature. What is the most likely explanation?
- Normal absorption of nitrogen into the refrigeration oil
- A leak exists somewhere in the system (Correct answer)
- Nitrogen is condensing inside the tubing at operating temperature
- The Bourdon gauge is reading low due to calibration drift
Correct answer: A leak exists somewhere in the system
Nitrogen does not condense or absorb into oil under normal conditions, so any measurable pressure drop during a standing test at constant temperature indicates a leak.
Question 6: Which type of electronic leak detector is best suited for detecting leaks of HFO refrigerants such as R-1234yf?
- Heated diode (halide) detector
- Infrared (IR) sensor detector (Correct answer)
- Heated pentode detector
- Ultrasonic acoustic detector
Correct answer: Infrared (IR) sensor detector
Infrared sensor detectors identify refrigerant by molecular absorption at specific IR wavelengths and can detect a broad range of HFC and HFO refrigerants including R-1234yf.
Question 7: After repairing a refrigerant system leak, what two steps are mandatory before recharging with refrigerant?
- Flush the system with dry nitrogen, then recharge immediately
- Perform a leak test, then evacuate the system to deep vacuum (Correct answer)
- Pressure test with refrigerant, then add a drier and recharge
- Run the compressor briefly on nitrogen, then recharge to nameplate weight
Correct answer: Perform a leak test, then evacuate the system to deep vacuum
A post-repair leak test confirms the repair is sound, and a deep vacuum evacuation removes air and moisture before refrigerant is introduced to prevent acid formation and system damage.
313A Piping, Brazing & Leak Detection 2
Which refrigerant leak detection method offers the highest sensitivity, capable of detecting leaks as small as 0.1 oz per year?