1997 Buick Park Avenue

Air Conditioning problem
1997 Buick Park Avenue 6 cyl Automatic 140000 miles

I have a strange problem. The car air conditioner works perfect as long as the temperature is not above 80 degrees. When temp gets hotter the air will not come out the vents. It only puts cold air on the windshield & a small amount in the floor. We recently replaced the air conditioner module & there is no change. Also for some time when you get in the car & the temp is hot the display will read c degree, f degree & the air conditioner will not come on at all for a long time & then finally down the road it will come on. The whole system will be shut down during this time. According to the manuel there is supposed to be a fuse panel directly under the instrument panel that has air conditioner fuses, but we have been unable to locate them. Any help you can offer would be appreciated. When the temp is in the 90's its pretty hot to drive home. In the fall & springtime when the temp is cooler the air works perfect. Go figure!