A vapor compression system comprises a compressor (22). The compressor comprises an inlet (40) and an outlet (42) and an electric motor (28). The motor has a stator (30) and a rotor (32). A plurality of bearings (36) support the rotor. A fluid flowpath (126) extends to the plurality of bearings. A branch (310) from the fluid flowpath extends to the compressor. A liquid sensor (330) is along the branch.