A vapor compression system (200; 300; 400) comprising: a compressor; a first heat exchanger; a second heat exchanger; an ejector comprising: a motive flow inlet; a secondary flow inlet; a motive nozzle with a throat section; and an outlet; a control needle movable between a first position and a second position; and an actuator for controlling the movement of the control needle, wherein the actuator is for shifting a tip portion of the needle into and out of the throat section of the motive nozzle to modulate flow through the motive nozzle; a separator having: an inlet; a liquid outlet; and a vapor outlet; an expansion device; a plurality of conduits positioned to define a first flowpath sequentially through: the compressor; the first heat exchanger; the ejector from the motive flow inlet through the ejector outlet; and the separator, and then branching into: a first branch returning to the compressor; and a second branch passing through the expansion device and second heat exchanger to the secondary flow inlet, wherein: the plurality of conduits are positioned to define a bypass flowpath (202; 302; 402) bypassing the motive nozzle and rejoining the first flowpath at essentially separator pressure but away from the separator; and the system further comprises a flow control device positioned to control flow along the bypass flow path and a controller configured to use the bypass flowpath for unloading of the ejector to relieve pressure of the high side components when the pressure relieved by fully withdrawing the control needle is insufficient. a compressor; a first heat exchanger; a second heat exchanger; an ejector comprising: a motive flow inlet; a secondary flow inlet; a motive nozzle with a throat section; and an outlet; a motive flow inlet; a secondary flow inlet; a motive nozzle with a throat section; and an outlet; a control needle movable between a first position and a second position; and an actuator for controlling the movement of the control needle, wherein the actuator is for shifting a tip portion of the needle into and out of the throat section of the motive nozzle to modulate flow through the motive nozzle; a separator having: an inlet; a liquid outlet; and a vapor outlet; an inlet; a liquid outlet; and a vapor outlet; an expansion device; a plurality of conduits positioned to define a first flowpath sequentially through: the compressor; the first heat exchanger; the ejector from the motive flow inlet through the ejector outlet; and the separator, and then branching into: a first branch returning to the compressor; and a second branch passing through the expansion device and second heat exchanger to the secondary flow inlet, the compressor; the first heat exchanger; the ejector from the motive flow inlet through the ejector outlet; and the separator, and then branching into: a first branch returning to the compressor; and a second branch passing through the expansion device and second heat exchanger to the secondary flow inlet, a first branch returning to the compressor; and a second branch passing through the expansion device and second heat exchanger to the secondary flow inlet, wherein: the plurality of conduits are positioned to define a bypass flowpath (202; 302; 402) bypassing the motive nozzle and rejoining the first flowpath at essentially separator pressure but away from the separator; and the system further comprises a flow control device positioned to control flow along the bypass flow path and a controller configured to use the bypass flowpath for unloading of the ejector to relieve pressure of the high side components when the pressure relieved by fully withdrawing the control needle is insufficient. the plurality of conduits are positioned to define a bypass flowpath (202; 302; 402) bypassing the motive nozzle and rejoining the first flowpath at essentially separator pressure but away from the separator; and the system further comprises a flow control device positioned to control flow along the bypass flow path and a controller configured to use the bypass flowpath for unloading of the ejector to relieve pressure of the high side components when the pressure relieved by fully withdrawing the control needle is insufficient.