To achieve the desired evaporator temperature, the power input should be adjusted by manipulating:

To achieve the desired evaporator temperature effectively, it is essential to maintain the correct balance between head pressure and suction pressure. Manipulating head pressure as low as possible allows for improved system efficiency and aids in optimizing the refrigerant flow through the evaporator. By keeping the head pressure at a lower level, the system requires less energy to compress the refrigerant, leading to better performance and energy savings.

Setting the suction pressure at an appropriate high level, on the other hand, ensures that the evaporator has sufficient pressure to allow for proper heat absorption from the environment. This combination of low head pressure and suitably adjusted suction pressure enables the system to maintain efficient cooling while achieving the desired evaporator temperature.

This approach recognizes that both pressures are integral to the refrigeration cycle and dictates how well the system can perform its cooling function. Therefore, the choice reflects the need for an appropriate balance in pressure settings to achieve optimal operational efficiency and temperature management.