1997 Buick Lesabre A/C problem

I have a 1997 Buick Lesabre Limited with automatic climate control A/C. As long as the outside temperature is below about 90 everything works fine. Above 90 when you get in the car and turn on the A/C it blows out the defrost and floor vents for a while and then gradually starts blowing out the vents like it should. The hotter it is, the longer this takes. When it`s above 100 you have to drive the car for about 10 miles before it finally starts blowing out the vents. Once it starts blowing out the vents like it should everything works perfect. Anyone out there have any ideas ? THANKS !

I would suspect the possibilty of a sticking actuator, or driver in the A/C control. I would be more concerned about the interior temperature of the vehicle as the cause. Ray