Ac stad for "Acromium clavicular joint", its the joint/ligament at the end of the collar bone ( Clavicle ), I did both of my Acj's in France this year ( August 2nd) back to work October 5th!!, i went straight to a physio when i got back and they gave me exercises to do consisting of the following exercises which were given to me by a trained physio thus i cannot accept any responsibility for any injury occuring from doing them. Do go and see a Physio they're there to help.
Exercises:
1. Put hand on shoulder with elbow pointing to front and raise and lower the elbow as far as it will go, use other arm to support if to painful!
2. As above but with elbow out to the side, repeat both for 5-10 reps up to 3 sets if you can manage, If it starts to hurt STOP! and do fewer reps.
3. Sit on a chair and put your damaged shoulder hand under your butt and stretch your neck to the opposite side, hold for 20 secs
Repeat the above up to 3 times a day for 2 weeks or until they're comfortable then you can do the same movements with your arm oustretched after that i suggest you see a Physiotherapist as they can give you more strength orientated exercises to do. It takes a while to get back to full strength but its progressive so dont get disheartened with with it, Good luck and make sure you do the exercises EVERY day