What effect does a rise in evaporator pressure have on the automatic expansion valve?

A rise in evaporator pressure is directly related to the function of an automatic expansion valve, which is designed to maintain a specific level of superheat and control the flow of refrigerant into the evaporator. When evaporator pressure increases, the automatic expansion valve responds to this change by opening. This opening action allows more refrigerant to flow into the evaporator to balance the heightened pressure, ensuring that the evaporator can absorb the appropriate amount of heat.

The principle behind this function is that the automatic expansion valve uses a sensing bulb or pressure sensing mechanism to monitor evaporator pressure. As the pressure rises, the valve's mechanism reacts by adjusting the orifice size, allowing more refrigerant to enter. This helps prevent the evaporator from becoming over-pressurized and ensures optimal performance of the system.

In contrast, the other choices involve scenarios where the valve would either close or remain closed, which would not effectively manage the rise in evaporator pressure, leading to inefficient cooling or even system failure. Therefore, the correct answer is that a rise in evaporator pressure causes the automatic expansion valve to open, facilitating proper refrigerant flow and maintaining system balance.