An illustrative example refrigerant system includes a compressor configured to pressurize a refrigerant fluid. The compressor includes a sump portion. A heater is situated to heat at least the sump portion. A controller is configured to selectively operate the heater to apply heat to at least the sump portion while the compressor is off to establish and maintain a superheat condition in the compressor.

A climate-control system may include a compressor and a control module. The compressor includes a motor driving a compression mechanism to compress a working fluid. The control module is in communication with the motor and may be configured to determine a balance speed of the motor at which a forward-rotational inertial force of the compression mechanism is equal to a backward-rotational gas force on the compression mechanism. The control module may be configured to adjust a running speed of the motor to the balance speed after receipt of a compressor-shutdown-command and before shutting down the compressor.

A freezing device including a compressor that compresses sucked refrigerant using a compression mechanism and discharges compressed refrigerant includes a compressor, an inverter, and a controller. The compressor includes a motor, a low pressure unit, a compression space, a high pressure unit, a communication flow path, and a flow control valve. The inverter drives or stops the motor. The controller controls the inverter and the flow control valve. The controller performs, in stop control in which an operation of the compressor is stopped, braking control in which driving of the compression mechanism is prevented or suppressed, and pressure equalization control in which pressure in the high pressure unit is equalized with pressure in the low pressure unit.

A refrigeration cycle apparatus includes a refrigeration cycle circuit, a liquid receiver, a first valve and a second valve. The refrigeration cycle circuit includes a compressor, an outdoor heat exchanger and an indoor heat exchanger. The liquid receiver is provided in a second section located in the refrigeration cycle circuit. The second section is a section extending between the outdoor heat exchanger and the indoor heat exchanger without extending through the compressor. The first valve is provided in a first section in the refrigeration cycle circuit, and is a solenoid valve or a motor valve. The first section is a section extending between the outdoor heat exchanger and the indoor heat exchanger through the compressor. The second valve is provided in the second section and between the liquid receiver and the indoor heat exchanger, and is an electronic expansion valve, a solenoid valve or a motor valve.

A compressor fault diagnostic apparatus including a current sensing unit to sense a current flowing through a motor of the compressor, a fault diagnostic unit to determine whether or not the motor performs a reverse rotation based on the current flowing through the motor, and a cut-off unit to remove power based on a determination of the fault diagnostic unit.

In a method for operating a compressor (22) having an inlet (26) and an outlet (28), the method includes: running the compressor to compress a fluid; shutting down (422) the compressor; determining (420) a condition-dependent threshold restart pressure difference (threshold) across the compressor; relieving the pressure difference to reach the threshold; and, after the threshold is reached, restarting (434) the compressor.

Systems and methods of operating a refrigeration system including initiating a compressor shutdown operation (302), recording shutdown conditions (304), calculating one or more restart characteristics based on the recorded shutdown conditions (306), comparing the calculated restart characteristics with one or more compressor restart safety limits (308), when the calculated restart characteristics do not satisfy the restart safety limits, performing a temperature modulation pump down operation (310), and when the calculated restart characteristics satisfy the restart safety limits, completing the compressor shutdown operation (312).

A refrigerant circuit of a refrigeration cycle apparatus has a compressor, a cooling-heating switching mechanism, a condenser, a refrigerant expansion mechanism, and an evaporator. During operation of the compressor, the refrigerant expansion mechanism opens the refrigerant circuit, a first three-way valve connects an outlet of the compressor to the condenser, and a second three-way valve connects an inlet of the compressor to the evaporator. During stop of the compressor, the refrigerant expansion mechanism closes the refrigerant circuit, the first three-way valve connects the outlet of the compressor to the evaporator, and the second three-way valve connects the inlet of the compressor to the evaporator.

An apparatus includes a microchannel heat exchanger, a load, a compressor, and a controller. The microchannel heat exchanger removes heat from a refrigerant. The load uses the refrigerant to remove heat from a space proximate the load. The compressor compresses the refrigerant from the load. The controller determines a discharge temperature of the refrigerant at the compressor and predicts a saturation temperature of the refrigerant between the compressor and the microchannel heat exchanger. The controller also determines a discharge superheat by subtracting the saturation temperature from the discharge temperature and triggers an alarm if the discharge superheat is below a threshold temperature.

An illustrative example refrigerant system includes a compressor configured to pressurize a refrigerant fluid. The compressor includes a sump portion. A heater is situated to heat at least the sump portion. A controller is configured to selectively operate the heater to apply heat to at least the sump portion while the compressor is off to establish and maintain a superheat condition in the compressor.