A rack of multiple compressors is controlled by which of the following?

The system controlling a rack of multiple compressors primarily utilizes the Crankcase Pressure Regulating valve (CPR) to maintain optimal performance across the entire refrigeration system. The CPR helps regulate the pressure within the crankcase of the compressors, ensuring that the operating conditions are maintained. This is crucial for preventing issues such as compressor flooding, which can occur when the pressure in the crankcase becomes too high.

The CPR plays a vital role in balancing the load among multiple compressors by allowing one or more compressors to take on the load while others remain inactive or operate at a lower capacity. By regulating the pressure, the CPR ensures that each compressor can function efficiently and effectively, thereby optimizing energy consumption and system reliability.

In contrast, the other options play different roles. A suction pressure transducer typically provides feedback on suction pressure but does not control the compressors directly. A thermostat mainly regulates temperature based on set points rather than managing compressor function. Interstage pressure is significant but primarily used in systems with multiple stages of compression; it does not oversee the coordination of compressors like a CPR does. This illustrative differentiation clarifies why the Crankcase Pressure Regulating valve is the best choice for controlling a rack of multiple compressors.