Free 313D Refrigeration Cycle Fundamentals Questions and Answers — Questions and Answers
Question 1: In a standard residential air conditioning system, what is the primary function of the evaporator coil?
- To compress low-pressure refrigerant gas into a high-pressure gas.
- To reject heat from the refrigerant to the outdoor air.
- To absorb heat from the indoor air, causing the refrigerant to boil. (Correct answer)
- To reduce the pressure of the high-pressure liquid refrigerant.
Correct answer: To absorb heat from the indoor air, causing the refrigerant to boil.
The evaporator coil is located indoors and is responsible for absorbing heat from the indoor air. As the warm indoor air is blown across the cold evaporator coil, the liquid refrigerant inside absorbs this heat and boils, changing its state from a liquid to a low-pressure gas.
Question 2: A technician measures the refrigerant leaving the condenser and finds it is a high-pressure liquid at a temperature below its saturation point. What is this condition called?
- Superheat
- Subcooling (Correct answer)
- Flashing
- Saturation
Correct answer: Subcooling
Subcooling is the process of cooling a liquid refrigerant below its condensation/saturation temperature. This ensures that only liquid refrigerant enters the metering device, which is crucial for system efficiency and performance.
Question 3: Which of the following components is responsible for creating a pressure differential that allows the refrigerant to change from a high-pressure liquid to a low-pressure liquid?
- Compressor
- Condenser
- Evaporator
- Metering Device (Correct answer)
Correct answer: Metering Device
The metering device (such as a TXV or capillary tube) creates a restriction in the flow of refrigerant. This restriction causes a significant drop in pressure, which in turn lowers the refrigerant's boiling point before it enters the evaporator.
Question 4: A residential AC system is running, and the compressor is functioning correctly. What is the expected state of the refrigerant as it enters the compressor?
- High-pressure, superheated vapor
- Low-pressure, subcooled liquid
- Low-pressure, superheated vapor (Correct answer)
- High-pressure, saturated liquid/vapor mix
Correct answer: Low-pressure, superheated vapor
The refrigerant leaves the evaporator as a low-pressure vapor. It should be slightly superheated, meaning its temperature is above its boiling point, to ensure no liquid refrigerant enters and damages the compressor.
Question 5: While diagnosing a system, a technician observes a very high superheat reading at the evaporator outlet. Which of the following is a potential cause?
- Refrigerant overcharge
- Dirty condenser coil
- Restricted liquid line filter drier (Correct answer)
- Non-condensables in the system
Correct answer: Restricted liquid line filter drier
A restricted liquid line filter drier will starve the metering device of refrigerant. This causes the refrigerant to flash off too early in the evaporator, leading to an excessive amount of superheat as the vapor travels through the remainder of the coil.
Question 6: What is the primary purpose of adding superheat to the refrigerant vapor before it leaves the evaporator?
- To increase the cooling capacity of the system.
- To ensure only vapor enters the compressor, preventing damage. (Correct answer)
- To lower the pressure of the refrigerant before condensation.
- To increase the efficiency of the condenser coil.
Correct answer: To ensure only vapor enters the compressor, preventing damage.
Superheat is the heat added to the refrigerant after it has completely boiled into a vapor. Its main purpose is to ensure that no liquid droplets travel back to the compressor, as liquid cannot be compressed and can cause severe mechanical damage (slugging).
Free 313D Refrigeration Cycle Fundamentals Questions and Answers
In a standard residential air conditioning system, what is the primary function of the evaporator coil?