What is the assumption made when reading pressure on the suction service valve with gauges?

The assumption that the pressure read at the suction service valve is the same as at the outlet of the evaporator is based on the principles of refrigeration cycle operation. In a vapor-compression refrigeration system, the evaporator absorbs heat and vaporizes the refrigerant, which then exits at a specific pressure corresponding to the evaporator's temperature.

Since the suction service valve is located at the inlet of the compressor, it directly measures the pressure of the vaporized refrigerant that has left the evaporator. In an ideal, well-functioning system, there should be minimal pressure drop between the evaporator outlet and the suction service valve. Thus, the pressure reading from the suction service valve accurately represents the evaporator's outlet pressure, allowing technicians to assess the system performance effectively.

Considering why the other choices do not accurately represent the situation: the pressure at the suction service valve is not inherently lower than the discharge pressure; instead, it is expected to be lower. The assumption about the pressure not being affected by ambient temperature is misleading, as temperature can affect pressure readings to some degree, especially if the system is not operating correctly. Lastly, the accuracy of the pressure reading is not limited to peak operation; it should provide a valid measure whether the system is under