AK-PC 781 is complete regulating units for capacity control of compressors and condensers in refrigeration systems. The controller is with oil management, heat recovery function and CO2 gas 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.