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 and continue operating the heater when the compressor turns on until a temperature of the compressor or a temperature of fluid discharged from the compressor satisfies at least one criterion.

An HVAC system includes a plurality of sensors, a tandem compressor, and a controller. The tandem compressor comprises a first and second compressor, each comprising a crankcase heater. The controller determines that one of the sensors has failed, and in response, initiates the first and second crankcase heaters and transmits an alert indicating that one of the sensors has failed. Further, the controller may disable threshold logic such that the first and second compressors are controlled independently of a determination whether the tandem compressor is operating outside of a threshold range. The controller operates the first and second compressors according to a safe mode, wherein first on or off settings of the compressors are determined based on a first required load operation of the tandem compressor. The first required load operation is determined from a first temperature demand of a structure associated with the HVAC system.

A climate-control system may include a compressor, a condenser, an evaporator, a first sensor, a second sensor, a third sensor, and a control module. The compressor may include a motor and a compression mechanism. The condenser receives compressed working fluid from the compressor. The evaporator is in fluid communication with the compressor and disposed downstream of the condenser and upstream of the compressor. The first sensor may detect an electrical operating parameter of the motor. The second sensor may detect a discharge temperature of working fluid discharged by the compression mechanism. The third sensor may detect a suction temperature of working fluid between the evaporator and the compression mechanism. The control module is in communication with the first, second and third sensors and may determine whether a refrigerant floodback condition is occurring in the compressor based on data received from the first, second and third sensors.

An air-conditioning apparatus includes: a refrigerant circuit in which a compressor, a four-way valve, a heat source-side heat exchanger, an expansion valve and a load-side heat exchanger are connected; and a controller which controls a refrigeration cycle in which refrigerant is circulated in the refrigerant circuit, to switch a flow passage for the refrigerant in accordance with which of a cooling operation, a heating operation and a defrosting operation is performed. The controller includes: a refrigeration-cycle control unit which controls the four-way valve to switch the flow passage of the refrigerant when the operation to be performed is switched from the heating operation to the defrosting operation; and a compressor control unit which sets an operation frequency of the compressor at a value lower than an operation frequency which is applied during the heating operation, when the operation is switched from the heating operation to the defrosting operation.

In order to improve a refrigerant compressor comprising a drive motor and a compressor unit which compresses a refrigerant entering through a suction inlet and allows it to exit through a pressure outlet in such a way that it works as reliably as possible, it is proposed that the refrigerant compressor comprise a compressor monitoring system which is integrated into a compressor control system and which determines a compressor condition by means of a first condition value that corresponds to a first saturation temperature in the suction inlet and a second condition value that corresponds to a second saturation temperature in the pressure outlet, and which compares the compressor condition with permissible compressor conditions lying in a given deployment field of a deployment diagram and initiates a process of switching-off the refrigerant compressor if the compressor condition departs from the deployment field.

In a refrigeration cycle apparatus, refrigerant circulates successively through a compressor, a condenser, an expansion valve, and an evaporator. The refrigeration cycle apparatus includes a detection unit, a heating unit, and a controller. The detection unit is configured to detect a temperature of refrigeration oil in the compressor. The heating unit is configured to heat the refrigeration oil. The controller is configured to operate the heating unit when the temperature detected by the detection unit is lower than a pour point of the refrigeration oil, and to stop the heating by the heating unit when the temperature detected by the detection unit reaches the pour point. Preferably, the heating unit includes a heater provided on an outer side of a compressor casing and at a lower portion of a motor unit.

A system may include first and second compressors, first and second heat exchangers, a flash tank, and first, second and third fluid paths. The first compressor may include first and second inlets. The second compressor may receive fluid from an outlet of the first compressor. The first heat exchanger may receive fluid from the second compressor. The flash tank may receive fluid from the first heat exchanger and includes a vapor outlet and a liquid outlet. The second heat exchanger may be in fluid communication with the flash tank and may receive fluid from the liquid outlet. The first fluid path extends from an outlet of the second heat exchanger to an inlet of the second compressor. The second fluid path extends from the vapor outlet to the first fluid path. The third fluid path may transmit fluid from the vapor outlet to the second inlet.

A control system controls the output capacity of a compressor to avoid surge conditions in the compressor. The control system determines a capacity control output for the compressor and then modifies the capacity control output in view of any output limiters or overrides as determined by system operating parameters and to maintain a minimum frequency of operation for the compressor.

A refrigerant compressor for refrigeration plants having a compressor unit driven by a drive unit. At least one of the compressor and drive units has a control unit which is controllable by delivery rate control system to control the refrigerant compressor at different delivery rates. An external delivery rate setpoint value is communicated to the delivery rate control system to prevent critical operating states. The delivery rate control system is configured to acquire, via a sensor, a compressor unit reference temperature. The delivery rate control system is configured to ascertain an operating state value group to acquire an operating state of the refrigerant compressor, and specify a delivery rate for operation of the refrigerant compressor outside of the critical operating states, if the value of the ascertained operating state value group based upon the compressor reference temperature permits a critical operating state of the refrigerant compressor.

A method of managing a compressor start operation, the method comprising controlling a valve disposed upstream of a compressor to lower a saturated suction temperature of a refrigerant to be below an ambient temperature while starting the compressor.