HVAC Refrigeration 4 — Questions and Answers
Question 1: What is the purpose of a hot gas bypass valve in a refrigeration system?
- Bypass hot discharge gas directly to the condenser during defrost
- Maintain minimum evaporator load by diverting hot gas to the evaporator inlet (Correct answer)
- Cool the discharge line during high ambient conditions
- Prevent refrigerant migration to the compressor during off cycles
Correct answer: Maintain minimum evaporator load by diverting hot gas to the evaporator inlet
A hot gas bypass valve diverts discharge gas to the evaporator inlet to maintain minimum system load and prevent evaporator freeze-up during low-load conditions.
Question 2: Which refrigerant is classified as A2L and is being adopted as an R-410A replacement?
- R-134a
- R-404A
- R-454B (Correct answer)
- R-22
Correct answer: R-454B
R-454B (sold as Puron Advance) is an A2L refrigerant with a GWP of 466 being adopted as the primary R-410A replacement in residential systems.
Question 3: In a refrigeration cycle, what happens to the refrigerant in the condenser?
- It absorbs heat and evaporates from liquid to vapor
- It is compressed from low pressure to high pressure vapor
- It rejects heat and condenses from vapor to liquid (Correct answer)
- It expands and drops in temperature
Correct answer: It rejects heat and condenses from vapor to liquid
In the condenser, high-pressure refrigerant vapor rejects heat to the outdoor air or water and condenses into a liquid.
Question 4: What is the purpose of crankcase heaters on a refrigeration compressor?
- Keep the compressor warm during operation to improve efficiency
- Prevent refrigerant from migrating to and mixing with the compressor oil during off cycles (Correct answer)
- Heat the discharge gas to prevent moisture condensation
- Warm the refrigerant in the suction line before compression
Correct answer: Prevent refrigerant from migrating to and mixing with the compressor oil during off cycles
Crankcase heaters keep the compressor oil warm during off cycles to prevent refrigerant from migrating into and diluting the oil, which can cause compressor damage on startup.
Question 5: What is 'coefficient of performance' (COP) in refrigeration?
- The ratio of refrigerating effect to compressor work input (Correct answer)
- The ratio of condenser heat rejection to evaporator heat absorption
- The percentage of refrigerant that remains as liquid at the evaporator inlet
- The measure of refrigerant purity after recovery
Correct answer: The ratio of refrigerating effect to compressor work input
COP is the ratio of the useful refrigerating effect (heat removed from the space) to the work input to the compressor, measuring the efficiency of a refrigeration system.
Question 6: According to EPA Section 608 regulations, technicians must use which type of equipment when removing refrigerant from a system?
- A nitrogen purging system
- EPA-approved refrigerant recovery equipment (Correct answer)
- A standard vacuum pump
- A refrigerant charging cylinder
Correct answer: EPA-approved refrigerant recovery equipment
EPA Section 608 requires technicians to use approved recovery equipment to capture refrigerant and prohibits venting it into the atmosphere.
Question 7: What condition is indicated when a refrigeration system has a high suction pressure and high discharge pressure simultaneously?
- Refrigerant overcharge (Correct answer)
- Low refrigerant charge
- Restricted liquid line filter-drier
- Compressor valve failure
Correct answer: Refrigerant overcharge
High suction and high discharge pressures together typically indicate an overcharged system, where excess refrigerant raises pressures throughout the system.
HVAC Refrigeration 4
What is the purpose of a hot gas bypass valve in a refrigeration system?