What could cause a vapor-cycle cooling system to freeze up?

In the context of a vapor-cycle cooling system, the correct answer centers on the issue of excessive moisture in the system. When there is too much water, it can lead to ice formation within the components of the cooling system, particularly in areas like the evaporator. The evaporator coil operates by absorbing heat from the cabin air, and the presence of excessive moisture can lead to condensation. If the temperature around these coils is low enough, this condensation turns into ice. This ice build-up can block the proper flow of refrigerant and severely reduce the efficiency of the system, eventually leading to a state where the cooling system freezes up entirely, causing operational failures.

Low refrigerant levels can also affect performance but typically create issues more related to cooling loss rather than direct freezing. High ambient temperatures would generally lead to increased performance needs from the system, making freezing less likely. Poor airflow can indeed result in cooling inefficiencies, but the relation to freezing is primarily through increased humidity levels condensing and freezing, which is exacerbated by excessive water in the system. Thus, the presence of too much moisture directly contributes to the likelihood of freeze-up in a vapor-cycle cooling system.