how can i fix my a/c 2001 olds aurora?

the ac in my 2001 olds aurora is not working correctly. it is a 4.0 v8 and has dual climate controls. the driver side and rear a/c seam to work the same. passanger side seams to work correctly most of the time but the driver side seams to only cool when the weather is not so hot. the hotter the weather the hotter the air blows. i have been told it is probably the blend door but i don't know how to fix it. please help