Which type of control can accomplish the operation of starting, stopping, and unloading the compressor?

The operation of starting, stopping, and unloading a compressor is most effectively accomplished through pressure control. This is because compressors are designed to operate in relation to specific pressure conditions within a system.

When the pressure drops below a predetermined setpoint, the pressure control system can signal the compressor to start operating, which helps to increase the pressure back to the desired level. Conversely, when the pressure reaches a set upper limit, the system can initiate a stop command to prevent over-pressurization, thereby protecting both the compressor and the connected equipment.

Additionally, unloading a compressor is a specific function controlled by pressure mechanisms. When the pressure in the system is sufficiently high, the control system can divert the flow of refrigerant or air, effectively unloading the compressor to prevent it from working under conditions where it could cause damage or inefficiency.

While temperature, flow, and electrical controls can influence compressor operation indirectly, they do not inherently manage the core functions of starting, stopping, and unloading in the same direct manner as pressure control. Hence, pressure control is the most appropriate and effective means of managing these critical operations.