313A Refrigeration Cycle

Question 1

What are the four main components of a basic vapour-compression refrigeration cycle?

Accepted Answer

Compressor, condenser, expansion valve, evaporator

Answer

The four essential components of a vapour-compression refrigeration cycle are: compressor (raises pressure and temperature), condenser (rejects heat), expansion device/metering device (reduces pressure), and evaporator (absorbs heat). Refrigerant flows through these components in a continuous cycle.

Question 2

In the refrigeration cycle, what state change does the refrigerant undergo in the evaporator?

Accepted Answer

Liquid to gas (evaporation/boiling)

Answer

In the evaporator, low-pressure liquid refrigerant absorbs heat from the space being cooled and changes state from liquid to gas (evaporation). This phase change absorbs a large amount of latent heat, which is what produces the cooling effect.

Question 3

What is superheat in the refrigeration cycle and why is it important?

Accepted Answer

The temperature above the boiling point of the refrigerant vapour leaving the evaporator; it ensures no liquid enters the compressor

Answer

Superheat is the temperature of the refrigerant vapour above its saturation (boiling) temperature at a given pressure. Measuring superheat at the evaporator outlet ensures all liquid has evaporated and only vapour enters the compressor, preventing liquid slugging that can damage the compressor.

Question 4

What is subcooling in the refrigeration cycle?

Accepted Answer

The temperature of the liquid refrigerant below its condensing (saturation) temperature at condenser pressure

Answer

Subcooling is the temperature difference between the actual liquid refrigerant temperature and its saturation temperature at condenser pressure. Adequate subcooling (typically 5°C to 10°C) ensures solid liquid reaches the metering device, improving system efficiency and indicating proper refrigerant charge.

Question 5

What is the relationship between pressure and boiling point of a refrigerant?

Accepted Answer

As pressure increases, the boiling point increases; as pressure decreases, the boiling point decreases

Answer

The boiling point of a refrigerant is directly related to its pressure. This principle is fundamental to refrigeration: the low-pressure side allows the refrigerant to boil at a low temperature (absorbing heat), while the high-pressure side forces it to condense at a higher temperature (rejecting heat).

Red Seal HVAC 313A Practice Test

Red Seal HVAC 313A Practice Test

313A Refrigeration Cycle