2003 Buick Park Avenue Solar Sensors do not seem to do anyt

Air Conditioning problem
2003 Buick Park Avenue 6 cyl Automatic 40,000 miles

There is basically nothing wrong with the air conditioner insofar as it producing extremely cold air so long as the fan is on 3 bars or above and the recycle is on. But it is supposed to do this automatically and it does not. Instead, when set to 75, as stated in the manual, and on automatic, it initially puts the fan on 5 bars and quickly cools the car. Within a short time the fan speed drops to two bars. After a few minutes the car becomes warmer & warmer until you notice the Air conditioner is not able to keep the car cool with the fan at 2 bars and not being on recycle. The only solution is to put the fan on 3 or 4 bars and recycle the air.

But this is what the automatic sensor(s) is/are supposed to do. But they never do. I have tested it for as long as 30 minutes and though the car got warmer and warmer the fan speed stayed on two bars. And the Recycle never was activated. Two days ago while the outside temperature was only 83, I was not even thinking about the Air conditioner but started feeling warm. I checked and the auto was on and set at 75. But the fan speed was 2 bars and the recycle was not on. I put the fan on 4 bars, recycle on, and the car became very comfortable.

Can this solar system be repaired or does the whole sensor system have to be replaced?

thanks