Refer too cold

I have a Kitchen Aid side by side refrigerator model # KSRS25FGWH02. The refrigerator side is too cold. I have replaced the temperature control thermostat with no result. If I put the temperature sensor in ice water, the air diffuser will not open until I slide the control to the coldest setting and will not close again until I put the slide in the off position. If the temperature sensor in out of the ice water, the air diffuser will open on the lowest setting and stay open even when I move the slide to the coldest coldest setting. If I move it to the off position it will close again.