CFC HVAC Systems & Leak Detection 3 — Questions and Answers
Question 1: Which of the following leak detection methods is most effective for locating very small leaks in inaccessible locations within HVAC ductwork?
- Soap bubbles
- Halide torch
- Ultrasonic detector (Correct answer)
- Nitrogen pressure test
Correct answer: Ultrasonic detector
Ultrasonic detectors sense the high-frequency sound produced by gas escaping through a small orifice, making them useful in noisy or hard-to-reach areas.
Question 2: A technician adds fluorescent UV dye to a system to locate a leak. How long should the system typically operate before performing a UV light inspection?
- 5 minutes
- 1–2 hours
- At least one full operating cycle or as specified by the dye manufacturer (Correct answer)
- 24–48 hours minimum
Correct answer: At least one full operating cycle or as specified by the dye manufacturer
UV dye must circulate throughout the system and accumulate at leak points; at least one full operating cycle is generally required before inspection.
Question 3: What pressure is typically used when performing a standing pressure test with nitrogen to check for leaks in a new HVAC installation?
- 150 psig for all systems
- The system's normal operating high-side pressure
- Pressure recommended by the equipment manufacturer or local code (Correct answer)
- 30 psig maximum
Correct answer: Pressure recommended by the equipment manufacturer or local code
Nitrogen pressure test levels should follow the equipment manufacturer's specifications or applicable codes, which vary by system type and refrigerant.
Question 4: Which refrigerant physical property makes CFC and HCFC leaks particularly difficult to visually detect compared to water leaks?
- High specific heat
- Colorless and nearly odorless vapor at room temperature (Correct answer)
- Low latent heat of vaporization
- High molecular weight
Correct answer: Colorless and nearly odorless vapor at room temperature
CFCs and HCFCs are colorless, nearly odorless gases at atmospheric pressure, providing no visual or olfactory clue of a leak.
Question 5: In a commercial refrigeration rack system, which area should a technician check FIRST when investigating a suspected refrigerant leak?
- Evaporator coil fins
- Schrader valve cores and caps (Correct answer)
- Compressor discharge muffler
- Condenser coil header
Correct answer: Schrader valve cores and caps
Schrader valve cores and missing or damaged caps are among the most common refrigerant leak points and should be checked first during any leak investigation.
Question 6: After repairing a refrigerant leak on a CFC system, what must a technician verify before returning the system to service?
- Only that the repaired joint holds pressure for 10 minutes
- That the repair holds, the system is recharged with the correct refrigerant amount, and leak-checked again (Correct answer)
- That the system cools to setpoint within 30 minutes
- That a new filter drier has been installed regardless of system condition
Correct answer: That the repair holds, the system is recharged with the correct refrigerant amount, and leak-checked again
Post-repair procedure requires confirming the fix is leak-free, recharging to the correct specification, and re-verifying no additional leaks exist.
Question 7: What does a 'standing pressure test' detect that a 'running pressure check' may miss?
- Low refrigerant charge
- Compressor efficiency losses
- Leaks that only occur under dynamic pressure fluctuations
- Static leaks present when the system is off and pressurized (Correct answer)
Correct answer: Static leaks present when the system is off and pressurized
A standing pressure test pressurizes a non-operating system and monitors for pressure drop over time, revealing static leaks not masked by system noise.
CFC HVAC Systems & Leak Detection 3
Which of the following leak detection methods is most effective for locating very small leaks in inaccessible locations within HVAC ductwork?