AK-PC 551 is used for capacity control of compressors and condensers in medium sized refrigeration systems and covers applications with one or two suction groups and a condenser. AK-PC 551 can control up to 8 compressors in a single suction group and it can control up to 4×4 compressors in 2 suction groups. A variety of compressor combinations are supported, including variable speed, digital scroll and 4-cylinder Stream compressors. Condenser fans can be controlled in steps (max 8) or via variable speed. AK-PC 551 can be fully configured through the built in or a remote display. Flexible configuration of 8 digital outputs, 8 analogue inputs, 8 digital inputs and 2 analogue outputs makes the controller highly adaptable to any pack application.