Abstract

A scroll-type refrigeration compressor is disclosed which incorporates an efficient, reliable, low cost modulation system employing a single actuator to effect switching between full and reduced capacity operation. The modulation system of the present invention includes an elongated member movably supported on the non-orbiting scroll which operates to ensure simultaneous opening and closing one or more unloading passages thus avoiding the possibility of even transient pressure imbalances between opposed compression pockets during operation of the compressor. In one embodiment, the elongated member has the opposite ends interconnected by springs and is rotatably movable to effect the intended modulation. In another embodiment, the elongated member is movable generally along a radial line of the non-orbiting scroll member. Further, the modulation system of the present invention provides for reduced capacity at both start up and shut down thus enabling the use of more efficient lower starting torque motors and reducing the potential for noise generating reverse rotation on shut down.