Method for controlling a refrigeration circle

In a refrigeration cycle electric signals for a capacity control valve 5 of a variable displacement compressor 1 and an electronic expansion valve 3 are directly measured. The differential pressure across the refrigeration cycle and the refrigerant flow rate are estimated based on these electric signals, to estimate the energy condition of the refrigeration cycle. Considering an engine rotational speed, the driving torque demand of the compressor is estimated, to carry out energy control for e.g. a maximum refrigerating capacity operation, maximum efficiency operation, required minimum refrigerating capacity operation, to save fuel consumption and to carry out energy control for reducing the burden on the engine e.g. during engine idling and acceleration.