Which of the following can cause freeze-up in a refrigeration system?

Water or water vapor in the refrigerant can lead to freeze-up in a refrigeration system because it can cause the formation of ice within the evaporator coils and other components. When water is present in the system, it can freeze at the low temperatures achieved during the refrigeration cycle, obstructing the flow of refrigerant. This ice formation may restrict airflow and lead to reduced efficiency or complete failure of the system.

Additionally, moisture in the refrigerant can also react with other components, leading to further complications such as corrosion or system failure. Therefore, maintaining a dry refrigerant charge is crucial to prevent freeze-ups and ensure the proper functioning of the refrigeration system.