Scroll compressor with back pressure chamber cavity for assisting in start-up

A scroll compressor comprising:

• a first scroll member having a base and a generally spiral wrap extending from its base, and a second scroll member having a base and a generally spiral wrap extending from its base;
• an electric motor for driving a shaft to cause said second scroll member to orbit relative to said first scroll member;
• a back pressure chamber defined behind a base of said second scroll member, said back pressure chamber receiving a tapped refrigerant from a compression chambers, said back pressure chamber biasing said first and second scroll members together, and a start-up cavity formed in said back pressure chamber to increase a volume of said back pressure chamber and reduce a starting load on said electric motor;
• and
• said start-up cavity extends for 360° about an axis of rotation of said shaft, said back pressure chamber is defined by an at least one seal received within a seal cavity, wherein said seal cavity extends for a depth away from said base of said one of said first and second scroll members, and said start-up cavity extends from said base for a second depth, with said second depth being greater than said first depth.