A refrigerant system comprising: a compressor, said compressor compressing refrigerant and delivering it downstream to a first heat exchanger, refrigerant passing from said first heat exchanger through a main expansion device positioned downstream of the first heat exchanger, through a second heat exchanger positioned downstream of said main expansion device, and from said second heat exchanger back to said compressor; an economizer expansion device positioned on a tap line for tapping at least a portion of refrigerant from a main refrigerant circuit, expanding this refrigerant to an intermediate pressure, and passing said tapped refrigerant in heat transfer relationship with the main refrigerant flow through an economizer heat exchanger; a bypass, said bypass bypassing refrigerant selectively around said main expansion device, around said economizer expansion device and around both said main expansion device and said economizer expansion device; wherein the bypass comprises a first bypass line for selectively bypassing at least a portion of refrigerant around said main expansion device, said first bypass line including a first auxiliary expansion device to provide expansion of the refrigerant flowing through said first bypass line, wherein said first auxiliary expansion device is a fixed restriction expansion device, and a second bypass line around said economizer expansion device also communicating at least a portion of said tapped refrigerant into said economizer heat exchanger through a second auxiliary expansion device, said tapped refrigerant being returned to said compressor at an intermediate compression point; a flow control device that allows for a refrigerant to bypass selectively around said main expansion device, around said economizer expansion device and around both said main expansion device and said economizer expansion device; and a control system arranged to block flow of refrigerant to the first and the second auxiliary expansion device when a relatively low refrigerant flow rate is required in the refrigerant system, and to unblock flow of refrigerant to the first and the second auxiliary expansion device when a relatively high refrigerant flow rate is required in the refrigerant system. a compressor, said compressor compressing refrigerant and delivering it downstream to a first heat exchanger, refrigerant passing from said first heat exchanger through a main expansion device positioned downstream of the first heat exchanger, through a second heat exchanger positioned downstream of said main expansion device, and from said second heat exchanger back to said compressor; an economizer expansion device positioned on a tap line for tapping at least a portion of refrigerant from a main refrigerant circuit, expanding this refrigerant to an intermediate pressure, and passing said tapped refrigerant in heat transfer relationship with the main refrigerant flow through an economizer heat exchanger; a bypass, said bypass bypassing refrigerant selectively around said main expansion device, around said economizer expansion device and around both said main expansion device and said economizer expansion device; wherein the bypass comprises a first bypass line for selectively bypassing at least a portion of refrigerant around said main expansion device, said first bypass line including a first auxiliary expansion device to provide expansion of the refrigerant flowing through said first bypass line, wherein said first auxiliary expansion device is a fixed restriction expansion device, and a second bypass line around said economizer expansion device also communicating at least a portion of said tapped refrigerant into said economizer heat exchanger through a second auxiliary expansion device, said tapped refrigerant being returned to said compressor at an intermediate compression point; a flow control device that allows for a refrigerant to bypass selectively around said main expansion device, around said economizer expansion device and around both said main expansion device and said economizer expansion device; and a control system arranged to block flow of refrigerant to the first and the second auxiliary expansion device when a relatively low refrigerant flow rate is required in the refrigerant system, and to unblock flow of refrigerant to the first and the second auxiliary expansion device when a relatively high refrigerant flow rate is required in the refrigerant system.