A centrifugal compressor assembly is provided. The centrifugal compressor assembly includes a scroll assembly having a suction plate defining an inlet fluid passage, a suction plate housing, a diffuser plate, and a collector. The suction plate is detachably coupled to the suction plate housing, the suction plate housing is detachably coupled to the collector, and the diffuser plate is detachably coupled to the collector. The centrifugal compressor assembly further includes an impeller rotatably mounted in the scroll assembly for compressing fluid introduced through the inlet fluid passage, and a variable geometry diffuser system.