I had ACL reconstruction on friday and my foot is cold, kind of numb and swollen. I've been moving it when not doing cpm. Should I go back to hospital?

Call Surgeon ASAP. There can be many explanations, but some are serious. If you had a nerve block, residual numbness can be normal. Try loosening the bandages. If the foot remains cold, it could represent an injury to the arteries and should be evaluated quickly.
Not a bad idea. If your foot is cold to touch and mum it could be a sign of a problem related to the arteries in your leg. If it remains cold, you may want to get checked out sooner rather than later. I hope this helps.
Call Surgeon NOW. While it "might" be normal, it could be a major problem, and is safer to assume the worst unless your surgeon says it's ok. Coldness and numbness could be an indication of inadequate blood flow to lower leg. If you can feel your dorsalis pedis pulse (easier to find, on top of foot, between 1st & 2nd toe, 1/4 to all the way up to ankle), that is good. If not, go to er for exam now.
Lossen Dressing. I would make sure the dressing is not too tight. If there is an ace wrap, I would remove it and see if the numbness and swelling improve. Otherwise, I would seek medical attention.