Air Conditioning Repair Refrigeration System Repair 5 — Questions and Answers
Question 1: What is the correct method for checking the refrigerant charge on a fixed-orifice system (piston or cap tube)?
- Target subcooling at the condenser outlet
- Target superheat at the evaporator outlet using manufacturer charts (Correct answer)
- Weigh in the exact nameplate charge
- Match suction pressure to outdoor ambient temperature
Correct answer: Target superheat at the evaporator outlet using manufacturer charts
Fixed orifice systems are charged by targeting a specific superheat value (typically using a charging chart based on indoor/outdoor conditions) rather than subcooling.
Question 2: A scroll compressor is running backwards due to incorrect wiring. What symptom will the technician observe?
- High suction and high discharge pressure
- Very low discharge pressure and high suction pressure with loud noise (Correct answer)
- Normal pressures but loud vibration
- Low suction pressure and no discharge pressure
Correct answer: Very low discharge pressure and high suction pressure with loud noise
A scroll compressor running in reverse produces very little compression, resulting in near-equal and abnormal pressures and often a distinctive noise.
Question 3: What does the term 'refrigerant migration' refer to in a refrigeration system?
- Refrigerant moving from the high side to the low side during operation
- Refrigerant traveling to and accumulating in the compressor crankcase during the off cycle (Correct answer)
- Refrigerant flowing through the metering device
- Normal refrigerant circulation during the cooling cycle
Correct answer: Refrigerant traveling to and accumulating in the compressor crankcase during the off cycle
Refrigerant migration occurs when refrigerant vapor moves toward the cold compressor oil during the off cycle, dissolving into the oil and causing compressor damage on startup.
Question 4: A tech is adding refrigerant to a system and notices the manifold gauge hoses feel very cold. What does this indicate?
- Normal charging operation
- The refrigerant cylinder is almost empty
- Liquid refrigerant is flowing through the hoses instead of vapor (Correct answer)
- The suction pressure is too low
Correct answer: Liquid refrigerant is flowing through the hoses instead of vapor
Cold hoses during charging indicate liquid refrigerant is entering the system, which can damage the compressor; vapor charging or a liquid metering device should be used.
Question 5: Which EPA regulation governs the handling, recovery, and recycling of refrigerants used in stationary HVAC equipment?
- Section 608 of the Clean Air Act (Correct answer)
- Section 609 of the Clean Air Act
- Title IV of the Clean Air Act
- ASHRAE Standard 15
Correct answer: Section 608 of the Clean Air Act
Section 608 of the Clean Air Act establishes technician certification requirements and regulations for refrigerant handling in stationary refrigeration and air conditioning equipment.
Question 6: What is the likely cause when a system's high-pressure switch trips repeatedly during hot summer days but not in moderate weather?
- Refrigerant overcharge
- Dirty or restricted condenser coil reducing heat rejection (Correct answer)
- Faulty low-pressure switch
- TXV stuck open
Correct answer: Dirty or restricted condenser coil reducing heat rejection
A dirty condenser coil restricts airflow and reduces the system's ability to reject heat, causing discharge pressure to rise above the high-pressure switch cutout on hot days.
Question 7: When brazing refrigerant lines, why is it important to flow dry nitrogen through the tubing during the brazing process?
- To pressurize the system for leak testing
- To prevent internal oxidation scale that could contaminate the refrigeration system (Correct answer)
- To cool the tubing faster after brazing
- To purge residual refrigerant before welding
Correct answer: To prevent internal oxidation scale that could contaminate the refrigeration system
Flowing nitrogen through tubing during brazing displaces oxygen and prevents copper oxide scale formation inside the lines, which can clog metering devices and damage compressors.
Air Conditioning Repair Refrigeration System Repair 5
What is the correct method for checking the refrigerant charge on a fixed-orifice system (piston or cap tube)?