What role do expansion devices play in refrigeration systems, and what pre-functional checks are necessary?

Expansion devices, such as expansion valves or capillary tubes, regulate refrigerant flow and pressure between the condenser and evaporator. Pre-functional checks on expansion devices involve verifying proper installation, inspecting for signs of wear or damage, and testing refrigerant flow rates and pressure drops. These checks ensure that the expansion device is operating correctly, maintaining optimal system performance and preventing issues like over- or under-feeding of refrigerant.