A refrigeration apparatus comprising a refrigerant circuit, the refrigerant circuit comprising: a compressor comprising a compressor fan and a motor to drive the compressor fan; a condensing device disposed downstream of the compressor, the condensing device comprising a condenser and a sub-cooler; an expansion valve disposed downstream of the condensing device; an evaporator disposed between the expansion valve and the compressor; a main refrigerant line fluidically connecting, in a loop in series: the compressor, condensing device, expansion valve and evaporator; and a motor cooling line comprising a motor cooling valve, the motor cooling line fluidically connecting the sub-cooler to the motor to tap refrigerant from the main refrigerant line to cool the motor, wherein the motor cooling line is further connected to the main refrigerant line at a return point which is upstream of the compressor fan to return refrigerant to the main refrigerant line at the compressor fan; characterised in that the refrigerant circuit further comprises a bypass line fluidically connecting an outlet of the condenser to the expansion valve to bypass the sub-cooler, wherein the bypass line comprises a bypass valve to selectively permit refrigerant in the main refrigerant line to bypass the sub-cooler; the refrigeration apparatus further characterised in comprising: a controller configured to control opening and closing of the bypass valve; and a first pressure sensor arranged to monitor the pressure of refrigerant exiting the sub-cooler, and a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the return point; wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor, and a second pressure parameter from the second pressure sensor, and to control the bypass valve based on the first pressure parameter and the second pressure parameter. a compressor comprising a compressor fan and a motor to drive the compressor fan; a condensing device disposed downstream of the compressor, the condensing device comprising a condenser and a sub-cooler; an expansion valve disposed downstream of the condensing device; an evaporator disposed between the expansion valve and the compressor; a main refrigerant line fluidically connecting, in a loop in series: the compressor, condensing device, expansion valve and evaporator; and a motor cooling line comprising a motor cooling valve, the motor cooling line fluidically connecting the sub-cooler to the motor to tap refrigerant from the main refrigerant line to cool the motor, wherein the motor cooling line is further connected to the main refrigerant line at a return point which is upstream of the compressor fan to return refrigerant to the main refrigerant line at the compressor fan; characterised in that the refrigerant circuit further comprises a bypass line fluidically connecting an outlet of the condenser to the expansion valve to bypass the sub-cooler, wherein the bypass line comprises a bypass valve to selectively permit refrigerant in the main refrigerant line to bypass the sub-cooler; the refrigeration apparatus further characterised in comprising: a controller configured to control opening and closing of the bypass valve; and a first pressure sensor arranged to monitor the pressure of refrigerant exiting the sub-cooler, and a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the return point; wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor, and a second pressure parameter from the second pressure sensor, and to control the bypass valve based on the first pressure parameter and the second pressure parameter. a controller configured to control opening and closing of the bypass valve; and a first pressure sensor arranged to monitor the pressure of refrigerant exiting the sub-cooler, and a second pressure sensor arranged to monitor the pressure in the main refrigerant line at the return point; wherein the controller is arranged to receive a first pressure parameter from the first pressure sensor, and a second pressure parameter from the second pressure sensor, and to control the bypass valve based on the first pressure parameter and the second pressure parameter.