Which of the following factors can be negatively affected by moisture in a refrigeration system?

Moisture in a refrigeration system can lead to several problematic outcomes, with acid formation, sludge formation, and ice in the expansion valve being significant issues. When moisture mixes with the refrigerant, it can cause chemical reactions that produce acids. These acids can corrode metal components, leading to system failures and costly repairs.

In addition, moisture can also lead to the formation of sludge, which can obstruct the flow of the refrigerant and negatively affect the overall system operation. The presence of moisture can freeze in critical areas like the expansion valve, obstructing the normal flow of refrigerant and thereby impacting the system's cooling performance.

While other choices may present concerns, the direct impact of moisture resulting in acid and sludge formation, as well as ice blockage, is the most immediately consequential factor that can heavily disrupt the functionality and efficiency of a refrigeration system. This specific knowledge is crucial for maintaining the reliability and efficiency of refrigeration operations.