the a/c blues

I just replaced the dryer on our 97 lesabre and put in new UV refidgerant, in case there was a leak. It ran cool as ICE for about 2weeks...now it is back to luke warm and it wants to only blow out the defroster and not the vents...plus there is no evidence of a leak because UV colorant does not show ....anyone have a clue cause I am at a loss HELP PLEASE