CFC HVAC Systems & Leak Detection 5 — Questions and Answers
Question 1: What is 'formicary corrosion' and why is it significant for HVAC leak detection?
- Corrosion caused by salt air that pits the outer surface of copper
- A form of copper corrosion caused by formic or acetic acid producing pinhole leaks (Correct answer)
- Galvanic corrosion between copper and aluminum coil fins
- Oxidation of copper joints from improper brazing technique
Correct answer: A form of copper corrosion caused by formic or acetic acid producing pinhole leaks
Formicary corrosion is caused by organic acids (formic, acetic) reacting with copper in the presence of moisture, creating characteristic tunnel-like pinholes that leak refrigerant.
Question 2: When recovering refrigerant from a system suspected of having a large leak, what precaution is most important before beginning recovery?
- Confirm the system is off and fully depressurized
- Identify the refrigerant type to use the correct recovery equipment and cylinders (Correct answer)
- Open all service valves to maximum before connecting recovery machine
- Add nitrogen to boost system pressure for faster recovery
Correct answer: Identify the refrigerant type to use the correct recovery equipment and cylinders
Identifying the refrigerant type is critical to avoid cross-contamination, use correct recovery equipment rated for that refrigerant, and comply with handling regulations.
Question 3: A technician measures compressor discharge temperature significantly above normal while suction pressure is below normal. What refrigerant system fault does this suggest?
- Refrigerant overcharge causing liquid slugging
- Low refrigerant charge causing high compression ratio and superheat (Correct answer)
- Dirty condenser coil causing high head pressure only
- Faulty thermostatic expansion valve stuck open
Correct answer: Low refrigerant charge causing high compression ratio and superheat
A low charge increases the compression ratio and allows excessive superheat to reach the compressor, raising discharge temperature well above normal.
Question 4: Which EPA record-keeping requirement applies when more than 50 pounds of refrigerant is added to a system during the calendar year?
- No records are required for repairs under 100 pounds
- The owner must maintain records of the refrigerant added and leak inspections performed (Correct answer)
- The technician must file a federal EPA report within 30 days
- Records must be sent to the refrigerant manufacturer quarterly
Correct answer: The owner must maintain records of the refrigerant added and leak inspections performed
EPA Section 608 requires owners of appliances with 50+ lbs of refrigerant to keep records of refrigerant added and to document leak inspection dates and results.
Question 5: In a heat pump system operating in heating mode, which pressure side should a technician probe first when searching for leaks using an electronic detector?
- Low-pressure suction side only, since it is the larger volume
- High-pressure discharge side, since higher pressure drives refrigerant through leak paths faster (Correct answer)
- Only the reversing valve, since it is the most common leak point in heat pumps
- The accumulator inlet, since that is where refrigerant pools
Correct answer: High-pressure discharge side, since higher pressure drives refrigerant through leak paths faster
Higher system pressure on the discharge side forces refrigerant through any existing leak path more rapidly, making leaks more detectable on the high side.
Question 6: What is the purpose of the 'low-loss fitting' required by EPA regulations on refrigerant recovery and charging hoses?
- To prevent refrigerant from flowing backward into the manifold
- To automatically close and minimize refrigerant release when hoses are disconnected (Correct answer)
- To regulate the flow rate during charging to prevent overcharge
- To filter moisture out of the refrigerant as it passes through the hose
Correct answer: To automatically close and minimize refrigerant release when hoses are disconnected
Low-loss fittings close automatically when disconnected, preventing refrigerant venting to the atmosphere during hose removal as required by EPA Section 608.
Question 7: A technician uses an electronic leak detector and finds a strong reading near the condenser coil header but no reading at fittings or joints nearby. What should the technician suspect?
- The detector is malfunctioning and needs calibration
- A hairline crack or pinhole in the tubing wall itself, not at a joint (Correct answer)
- Refrigerant migration from a distant leak elsewhere in the system
- Contamination of the detector sensor from previous use
Correct answer: A hairline crack or pinhole in the tubing wall itself, not at a joint
Refrigerant concentrated at a mid-tube location rather than at fittings suggests a crack, corrosion pit, or pinhole in the tubing wall itself, common in older coils.
CFC HVAC Systems & Leak Detection 5
What is 'formicary corrosion' and why is it significant for HVAC leak detection?