Thats a good point that I overlokked. The foam in the sight glass is a strong indicator of liquid mixing with the oil however. Also, it sounds as if the compressor is oversized for the system. If one unloader is NEVER loaded and the other cycles often, is it not possible that the TXV is hunting which would allow liquid to pass through into the compressor in varying amounts? That would account for the different amounts of foam (liquid) that is seen in the sight glass?