When starting a refrigerating compressor after a shutdown period, which valve should you manually throttle?

When starting a refrigerating compressor after a shutdown period, manually throttling the suction side of the compressor is important to ensure a smooth and safe startup. Throttling the suction valve helps to control the flow of refrigerant entering the compressor, which can prevent the compressor from drawing in too much refrigerant vapor too quickly.

If a compressor is started with unrestricted suction, it could lead to a condition known as liquid slugging, where liquid refrigerant is drawn into the compressor. This can cause mechanical damage because compressors are designed to compress vapor, not liquid. By throttling the suction side, the operator can gradually increase the flow and allow the compressor to build up pressure and temperature safely before reaching full operational capacity.

The other options involve different components that do not directly aid in controlling the intake of refrigerant during startup. The discharge side and expansion valve relate to how refrigerant exits and how it's regulated past the evaporator, respectively, and the bypass valve is not typically manipulated during a standard startup process. Thus, focusing on the suction side provides the necessary control for a safe compressor startup.