cam not working after yosemite

I have been looking a few days now for a real answer to this . A week ago or so I had mavericks. my cam worked fine. I updated to Yosemite and the cam is no longer detected. Even in system under cameras it does not show up. I went back to mavericks and still no cam. for the fun of it i went back to 10.7.5. no cam. Any one have a fix for this ? Yes I have reset SMC and Pram. in fact i have tried every thing i think of. I even have another air that works fine so i swapped complete top cases , still no cam. but the cam off the non working air is now on the working one and working . every thing was fine till i went to Yosemite. Any suggestions ? its a mid 2011, 11 inch air i5,