What phenomenon could be indicated by the presence of high superheat in a refrigeration system?

High superheat in a refrigeration system typically indicates that the refrigerant is receiving excessive heat after it has completely vaporized in the evaporator and before it enters the compressor. This condition can arise when the surface area of the evaporator is insufficient to absorb the heat load or when there is insufficient refrigerant flow due to a restriction.

In this context, when a malfunctioning expansion valve occurs, it may incorrectly restrict the flow of refrigerant into the evaporator. This restriction can lead to the refrigerant evaporating more completely and becoming over-energized in the evaporator, resulting in higher than normal superheat. Proper functioning of the expansion valve ensures that the correct amount of refrigerant enters the evaporator, maintaining the desired superheat levels.

While high superheat can indeed signal various issues — such as a system being overcharged or problems related to flooding — the most direct indicator in this scenario is the state of the expansion valve, making it the correct choice.