Final answer:
Under heavy load, a constant-pressure expansion valve will open wider to allow more refrigerant into the evaporator, leading to flooding of the evaporator to ensure adequate cooling capacity is met.
Step-by-step explanation:
In a refrigeration system, an expansion valve plays a crucial role in regulating the flow of refrigerant, responding to the load conditions of the evaporator. During periods of heavy load, the demand for cooling increases, causing more refrigerant to be required in the evaporator to absorb the additional heat. A constant-pressure expansion valve is designed to maintain a steady evaporator pressure, and under heavy load, it will open wider to allow more refrigerant to flow into the evaporator. This action typically results in the evaporator being flooded with refrigerant to ensure it can meet the demanded cooling capacity, thus preventing the evaporator from being starved of refrigerant. However, excessive flooding can lead to inefficiencies such as a decrease in superheat and potential compressor damage if the liquid refrigerant returns to the compressor. Therefore, the correct response to the question is that under a heavy load, a constant-pressure expansion valve will flood the evaporator.