What system component is crucial for establishing a minimum operating pressure in the evaporator?

The low pressure cut-out switch is essential for maintaining a minimum operating pressure in the evaporator. This component monitors the pressure within the evaporator and is designed to shut off the system if the pressure falls below a certain threshold, which can be indicative of potential problems such as low refrigerant levels or issues with heat absorption. By ensuring that the pressure does not drop below acceptable levels, the low pressure cut-out switch helps to protect the evaporator from damage and maintains efficient system operation.

In contrast, the high pressure switch is typically concerned with preventing excessively high pressures, while the oil pressure switch monitors the oil system's pressure to ensure proper lubrication of the compressor. The expansion valve is responsible for regulating the flow of refrigerant into the evaporator, but it does not directly control the operating pressure. Therefore, the low pressure cut-out switch plays a critical role in maintaining the necessary conditions for the evaporator's functioning, making it the correct answer.