2001 Buick LaSabre, A/C problem

I have a 2001 Buick LaSabre with dual climate controls for the driver and passenger sides, the passenger side blows nice and cold but the drivers side only blows warm air on the coldest setting. I have had it to 2 diff. Mechanics and neither one knows what the cause is or how to solve the problem. does anyone have any ideas as to a cause or solution to the problem? Summer is already here in N.M. and my wife is not happy when she is burning up, Thanks for any help you might provide.