ANY MECHANICS OUT THERE OR PPL WITH SIMILAR CAR PROBLEMS??

ok so one day a month ago i was just riding around having a nice day blowing my air. then all of a sudden my car cuts off. it would crank back up bu have a grinding sound then cut back off. well come to find out it only does that when the air is on or when the defrost is on whether heat or air. but it doesn't do that when the heat is on. only when the defrost heat or air and the air is on. wtf could be the problem. i owuld've got it taken care of but i have to get the money up because chevy charges 100 just to check the damn thing. btw does anyone know if warranty cover it