A compressor system for compression of refrigerant fluid, the compressor system comprising: a first compressor element for compression of the refrigerant fluid, the first compressor element being within a first compressor element housing; a second compressor element for compression of the refrigerant fluid, the second compressor element being within a second compressor element housing; an equalisation line that fluidly connects the first and second compressor element housings (4, 8) in order to allow for equalisation of pressure between the first and second compressor element housings (4, 8) as well as flow of lubricant between the compressor element housings (4, 8); and an equalisation valve on the equalisation line for opening and closing the connection between the first and second compressor element housings (4, 8) via the equalisation line; wherein the compressor system is arranged for full load operation using both the first and second compressor elements ( 2, 6) as well as for part load operation in which one of the compressor elements (2, 6) is not utilised; wherein the compressor system is arranged to open the equalisation valve during full load operation; and wherein the compressor system is arranged to close the equalisation valve during part load operation to thereby prevent movement of lubricant and/or refrigerant fluid between the first and second compressor element housings (4, 8) during part load operation; characterised in that the equalisation line fluidly connects the first and second compressor element housings (4, 8) at the suction side; and the compressor elements (2, 6) provide differing capacities and/or at least one compressor element (2, 6) provides a varying capacity. a first compressor element for compression of the refrigerant fluid, the first compressor element being within a first compressor element housing; a second compressor element for compression of the refrigerant fluid, the second compressor element being within a second compressor element housing; an equalisation line that fluidly connects the first and second compressor element housings (4, 8) in order to allow for equalisation of pressure between the first and second compressor element housings (4, 8) as well as flow of lubricant between the compressor element housings (4, 8); and an equalisation valve on the equalisation line for opening and closing the connection between the first and second compressor element housings (4, 8) via the equalisation line; wherein the compressor system is arranged for full load operation using both the first and second compressor elements ( 2, 6) as well as for part load operation in which one of the compressor elements (2, 6) is not utilised; wherein the compressor system is arranged to open the equalisation valve during full load operation; and wherein the compressor system is arranged to close the equalisation valve during part load operation to thereby prevent movement of lubricant and/or refrigerant fluid between the first and second compressor element housings (4, 8) during part load operation; characterised in that the equalisation line fluidly connects the first and second compressor element housings (4, 8) at the suction side; and the compressor elements (2, 6) provide differing capacities and/or at least one compressor element (2, 6) provides a varying capacity.