vent on dash on 1996 Cadillac Eldorado

when air is on the air fromone side (pass) is cold the other side is hot a vent in the dash is not opening (I used to hear this )

Asked by for the 1996 Cadillac Eldorado
sounds like the condensor core or whatever houses the vacuum accuated levers under glove box has problem. could be there is a vacuum problem that is not actuating all the vent louvers that move when you change from dash to defrost to floor ect... or the louvers are actually broken.