Hi everyone ! My cakes seem to sweat after I frost them put them in the fridge and take them out and put fondant on them. 

Why foes led this happen ! I want my frosting to be hard before putting my fondant on :(

It's a normal physical reaction.  It happens any time a cold object comes into contact with warm, moist air---like the condensation that forms on a glass of ice tea on a hot day.

Best solution is to leave the cake in the fridge only long enough for the icing to get cold, but not long enough for the cake itself to get cold.  That will keep the condensation to the very minimum, if any formed at all.