AK-PC 783 is complete regulating units for capacity control of compressors and condensers in refrigeration plants with cascade function. The controller controls the high-pressure circuit, low-pressure circuit and cascade circuit. The controller is with oil management, simple heat recovery function and coordination between the high-pressure control and low-pressure control. In addition to capacity control the controllers can give signals to other controllers about the operating condition, e.g. forced closing of expansion valves, alarm signals and alarm messages. The controller’s main function is to control compressors and condensers so that operation all the time takes place at the energy-optimum pressure conditions. Both suction pressure and condensing pressure are controlled by signals from pressure transmitters.