A refrigerant system comprising: a compressor assembly including at least two stages of compression connected in series, with a lower compression stage compressing refrigerant from a suction pressure to an intermediate pressure and passing this refrigerant to a higher compression stage compressing refrigerant from an intermediate pressure to a discharge pressure; an intercooler (26;126) positioned intermediate of said lower and higher compression stages; a liquid/vapor injection function with a liquid/vapor injection line leading to a vapor injection connection positioned intermediate of said lower and higher compression stages; a heat rejecting heat exchanger (30;130) positioned downstream of said higher compression stage, an evaporator (32;132) positioned upstream of said lower compression stage and an expansion device (40;140) positioned intermediate of said heat rejecting heat exchanger (30;130) and said evaporator (32;132); at least one secondary fluid moving device (34;134) for moving secondary fluid in at least one secondary fluid path over said heat rejecting heat exchanger (30;130) and said intercooler (26;126); and said intercooler (26;126) and said liquid/vapor injection function are selectively activated to control refrigerant discharge temperature depending on environmental and operational conditions as well as thermal load demands in a conditioned space, characterised in that: the system further comprises an intercooler bypass line incorporating a refrigerant flow control device; and the liquid/vapor injection line incorporates an auxiliary expansion device with shutoff functionality; wherein the intercooler (26;126) is selectively activated using the refrigerant flow control device, and the liquid/vapor injection function is selectively activated using the shutoff functionality of the auxiliary expansion device. a compressor assembly including at least two stages of compression connected in series, with a lower compression stage compressing refrigerant from a suction pressure to an intermediate pressure and passing this refrigerant to a higher compression stage compressing refrigerant from an intermediate pressure to a discharge pressure; an intercooler (26;126) positioned intermediate of said lower and higher compression stages; a liquid/vapor injection function with a liquid/vapor injection line leading to a vapor injection connection positioned intermediate of said lower and higher compression stages; a heat rejecting heat exchanger (30;130) positioned downstream of said higher compression stage, an evaporator (32;132) positioned upstream of said lower compression stage and an expansion device (40;140) positioned intermediate of said heat rejecting heat exchanger (30;130) and said evaporator (32;132); at least one secondary fluid moving device (34;134) for moving secondary fluid in at least one secondary fluid path over said heat rejecting heat exchanger (30;130) and said intercooler (26;126); and said intercooler (26;126) and said liquid/vapor injection function are selectively activated to control refrigerant discharge temperature depending on environmental and operational conditions as well as thermal load demands in a conditioned space, characterised in that: the system further comprises an intercooler bypass line incorporating a refrigerant flow control device; and the liquid/vapor injection line incorporates an auxiliary expansion device with shutoff functionality; wherein the intercooler (26;126) is selectively activated using the refrigerant flow control device, and the liquid/vapor injection function is selectively activated using the shutoff functionality of the auxiliary expansion device. the system further comprises an intercooler bypass line incorporating a refrigerant flow control device; and the liquid/vapor injection line incorporates an auxiliary expansion device with shutoff functionality; wherein the intercooler (26;126) is selectively activated using the refrigerant flow control device, and the liquid/vapor injection function is selectively activated using the shutoff functionality of the auxiliary expansion device.