A compressor (22) comprises: a housing (50); a shaft (70); a plurality of bearings (66, 67, 68, 74, 76) mounting the shaft to the housing for relative rotation about an axis (500); and a motor (52). The motor has: a rotor (64) mounted on the shaft; and a stator (62). A first impeller (54A) is mounted the shaft to a first side of the motor. A second impeller (54B) is mounted the shaft to a second side of the motor. The first impeller is an open impeller and the second impeller is a shrouded impeller.