I've always diagnosed a mid-way stuck r-valve by following the heat of the compressor discharge through the r-valve and back to compressor suction. The discharge gas has no problem getting hot and hotter as it is short cycled.
But yesterday I observed the same thing but the discharge took a while to get a little warm and never got really hot like I would expect.
This was a Copeland scroll ZRK5. Can anyone explain why?