I have a 2007 Chevy Aveo. The heater/defroster worked great last winter, but I tried using it the other day and the blower is working but it is putting out only slightly warm air. Not hot air like in the past. And when I switch it from heat to defrost/heat combo or just defrost the air gets cooler. I've already checked the coolant and it's full. Any ideas of what the problem might be?