Which condition indicates evaporator temperature in the engine room?

The condition that indicates evaporator temperature in the engine room is suction pressure. This is critical because the evaporator absorbs heat from the environment and is part of the refrigeration cycle. When refrigerant evaporates in the evaporator, it turns from liquid to gas, which corresponds directly to the suction pressure measured at the compressor inlet.

As the refrigerant vaporizes, the pressure decreases in the evaporator, which allows the system to maintain efficiency in heat absorption. Therefore, monitoring suction pressure provides insight into the evaporator's performance and efficiency. A drop in suction pressure typically indicates that the evaporator is effectively absorbing heat, while an increase might suggest issues such as blockages or insufficient refrigerant flow, leading to less effective cooling.

Other options like discharge pressure, slide valve percentage, and suction temperature at the compressor inlet can provide useful information about different parts of the refrigeration cycle, but they do not directly reflect the condition of the evaporator temperature itself.