A fluid displacement apparatus includes a housing for receiving a refrigerant, a driving shaft rotatably received in the housing, a magnetic clutch attached to the driving shaft for rotation transmitting purposes, a fixed scroll disposed in the housing, an orbiting scroll rotatably received and engaged in the housing and interfitting with the fixed scroll for compressing the refrigerant and for generating a pressurized refrigerant, the housing includes a compartment communicating with the inner chamber of the housing with a passage for receiving a pressure sensing device which may sense the pressure of the pressurized refrigerant for detecting whether the refrigerant in the housing is over pressure or not.