The shutdown of a compressor (10) installed in a
refrigerant circuit (2) in
air conditioning or
refrigeration system is controlled so as to prevent unpowered reverse rotation of the compressor. Prior to terminating
electric power to the compressor
drive motor (24), the pressure within the
system is relieved and substantially equalized across the compressor, thereby eliminating the possibility of unpowered reverse rotation of the compressor at shutdown. Pressure relief and
equalization may be achieved by reducing the
operating speed of the compressor to a low
forward speed for a period of time prior to deenergizing the compressor
drive motor. Pressure
equalization may also be achieved by driving the compressor in reverse rotation prior to deenergizing the
drive motor.