Compressor having capacity modulation system

A compressor may include first and second scrolls, a seal assembly and a valve ring. The first scroll may include a first end plate having a discharge passage, a modulation port, and a biasing passage. The modulation port may be in communication with a first pocket formed between spiral wraps of the first and second scrolls. The biasing passage may be in communication with a second pocket formed between spiral wraps of the first and second scrolls. The modulation valve ring is axially displaceable relative to the seal assembly and the first scroll between first and second positions. The valve ring may abut an end plate of the first scroll and close the modulation port when in the first position. The valve ring may abut an axially-facing surface of the seal assembly and is spaced apart from the end plate to open the modulation port when in the second position.