NATE Refrigeration 2

Question 1

What refrigerant is used in low-temperature frozen food applications and has an evaporating temperature around -20°F?

Accepted Answer

R-404A or R-448A

Answer

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?

Accepted Answer

Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters

Answer

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?

Accepted Answer

High condensing pressure and/or low evaporating pressure

Answer

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?

Accepted Answer

Separate compressor oil from the discharge gas and return it to the compressor crankcase

Answer

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?

Accepted Answer

Difference between return air temperature and saturated suction temperature in the evaporator

Answer

Evaporator TD is the difference between the air entering the coil and the saturated suction temperature, indicating heat transfer efficiency.

NATE - North American Technician Excellence Practice Test