I have a strange problem with my heat that is driving me nuts. Yesterday it was fine, but this morning it only blows on the high setting. When I turn the knob to the third to first settings, nothing. Now when I turn it to the dash vents, it only blows on defroster. The heat is hot, thats not the problem. We did have ice and snow last night and it is 15 degrees out, would thatcause any problems?