What happened to my AC
 

This past summer I was on my Bluetooth phone connection in my 2011 gmc 3500HD . When talking on the phone the A.C. blower motor reduces speed so that you can here better while talking.on the phone .At the end of the phone call when you hang up the fan speed returns to its previous setting. It did not return to the earlier setting nor did it come back on at all .I have replaced the blower motor resister no change. Ideas