Control of refrigerant flow, temperatures, pressures, and liquid levels is essential in any refrigeration system. This chapter describes a variety of devices and their application to accomplish these important control functions. Most examples, references, and capacity data in this chapter refer to the more common refrigerants. For further information on control fundamentals, see Chapter 7 of the 2021 ASHRAE Handbook—Fundamentals and Chapter 47 of the 2019 ASHRAE Handbook—HVAC Applications. CONTROL SWITCHES Pressure Switches Temperature Switches (Thermostats) Differential Switches Float Switches CONTROL SENSORS Pressure Transducers Thermistors Resistance Temperature Detectors Thermocouples Liquid Level Sensors CONTROL VALVES Thermostatic Expansion Valves Electric Expansion Valves REGULATING AND THROTTLING VALVES Evaporator-Pressure-Regulating Valves Constant-Pressure Expansion Valves Suction-Pressure-Regulating Valves Condenser-Pressure-Regulating Valves Discharge Bypass Valves High-Side Float Valves Low-Side Float Valves Solenoid Valves Condensing Water Regulators Check Valves Relief Devices DISCHARGE-LINE LUBRICANT SEPARATORS CAPILLARY TUBES Adiabatic Capillary Tube Selection Procedure Capillary-Tube/Suction-Line Heat Exchanger Selection Procedure SHORT-TUBE RESTRICTORS