What will cause the suction line temperature to increase?

The correct answer relates to an increase in heat load within the system. When the heat load increases, more heat is absorbed by the refrigerant in the evaporator. This additional heat raises the temperature of the refrigerant vapor in the suction line as it returns to the compressor. An increase in heat load indicates that there are more thermal loads requiring cooling, which necessitates the refrigerant absorbing more heat, subsequently raising the suction line temperature.

Improved insulation, on the other hand, would help maintain lower temperatures in the suction line by reducing heat gain from the surrounding environment. Lower refrigerant flow could actually lead to less heat transfer and potentially lower temperatures, as less refrigerant is circulating to absorb heat. Lastly, increased refrigerant pressure does not directly lead to a temperature increase in the suction line; while it might indicate a higher pressure condition in the system, a higher pressure in the suction line is not synonymous with increased temperature unless significant heat is also introduced.