NATE Refrigeration 2 — Questions and Answers
Question 1: What refrigerant is used in low-temperature frozen food applications and has an evaporating temperature around -20°F?
- R-410A
- R-404A or R-448A (Correct answer)
- R-22
- R-134a
Correct answer: R-404A or R-448A
R-404A and its replacement R-448A are designed for low and medium-temperature commercial refrigeration systems.
Question 2: What is the purpose of a hot gas defrost system in commercial refrigeration?
- Reheat supply air after cooling
- Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters (Correct answer)
- Warm the compressor oil at startup
- Prevent condensation on the case glass doors
Correct answer: Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters
Hot gas defrost diverts discharge gas from the compressor into the evaporator to melt frost quickly and efficiently without electric heaters.
Question 3: What causes a high compression ratio in a refrigeration system?
- Low ambient temperature
- High condensing pressure and/or low evaporating pressure (Correct answer)
- Oversized metering device
- High suction superheat only
Correct answer: High condensing pressure and/or low evaporating pressure
Compression ratio is head pressure divided by suction pressure; it rises when the condenser is hot (high head) or evaporator is cold (low suction).
Question 4: What is the function of the oil separator in a commercial refrigeration system?
- Remove moisture from refrigerant
- Separate compressor oil from the discharge gas and return it to the compressor crankcase (Correct answer)
- Filter non-condensables from the system
- Regulate oil temperature
Correct answer: Separate compressor oil from the discharge gas and return it to the compressor crankcase
Oil separators prevent excessive oil migration through the system, ensuring the compressor maintains adequate lubrication.
Question 5: What is the typical evaporator TD (temperature difference) used to assess evaporator performance in a refrigeration system?
- Difference between condensing temperature and ambient
- Difference between return air temperature and saturated suction temperature in the evaporator (Correct answer)
- Difference between supply and return air temperatures
- Difference between discharge and suction pressures in degrees
Correct answer: Difference between return air temperature and saturated suction temperature in the evaporator
Evaporator TD is the difference between the air entering the coil and the saturated suction temperature, indicating heat transfer efficiency.
Question 6: What EPA regulation governs refrigerant handling and requires recovery before service of commercial refrigeration equipment?
- EPA Section 404
- EPA Section 608 (Correct answer)
- Clean Water Act
- OSHA 29 CFR 1910
Correct answer: EPA Section 608
EPA Section 608 prohibits venting refrigerants and requires certified technicians to recover refrigerant before opening any refrigerant circuit.
NATE Refrigeration 2
What refrigerant is used in low-temperature frozen food applications and has an evaporating temperature around -20°F?