Refrigeration Cycle Fundamentals Flashcards

In a standard refrigeration cycle, what is the primary function of the compressor?

Answer: To increase the pressure and temperature of the refrigerant vapor.

The compressor acts as the heart of the system, taking in low-pressure, low-temperature refrigerant vapor and compressing it into a high-pressure, high-temperature vapor. This process is essential for moving the refrigerant through the cycle and enabling heat transfer in the condenser.

A residential air conditioning system is running, but the indoor unit is not blowing cold air. A technician measures the refrigerant state at the outlet of the evaporator coil and finds it is a saturated mixture. What does this condition most likely indicate?

Answer: The metering device is allowing too much refrigerant into the evaporator.

The refrigerant should leave the evaporator as a superheated vapor, meaning it has absorbed enough heat to completely boil off and then some. A saturated mixture (part liquid, part vapor) at the outlet indicates that not all the liquid refrigerant has boiled off, a condition known as 'flooding.' This is often caused by an overfeeding metering device or a severely restricted airflow over the evaporator.

Which of the following describes the state of the refrigerant as it enters the metering device in a properly functioning air conditioning system?

Answer: High-pressure, warm liquid

After leaving the condenser, the refrigerant has rejected heat to the outdoors and has condensed from a high-pressure vapor into a high-pressure, warm liquid. This subcooled liquid then flows to the metering device.

What is the primary purpose of the subcooling process that occurs in the condenser?

Answer: To prevent flash gas from forming before the metering device.

Subcooling is the process of cooling the liquid refrigerant below its saturation temperature after it has fully condensed. This ensures that a solid column of liquid refrigerant reaches the metering device, preventing bubbles of vapor (flash gas) from forming prematurely, which would reduce the efficiency of the metering device and the evaporator.

During the refrigeration cycle, where does the refrigerant absorb heat from the space being cooled, causing it to change from a liquid to a vapor?

Answer: In the evaporator

The evaporator is the component located inside the space being cooled. As the low-pressure, low-temperature liquid refrigerant flows through the evaporator coil, it absorbs heat from the indoor air, causing the refrigerant to boil and change into a low-pressure vapor.

What is the primary function of a metering device, such as a thermostatic expansion valve (TXV) or a fixed orifice, in a residential air conditioning system?

Answer: To create a large pressure drop in the refrigerant.

The metering device's main role is to create a significant pressure drop between the high-pressure side (condenser) and the low-pressure side (evaporator) of the system. This rapid pressure reduction causes the high-pressure liquid refrigerant to become a very cold, low-pressure mixture of liquid and vapor, ready to absorb heat in the evaporator.