I have a 2001 Vulcan Taurus SES. Last January I purchased the car and the heat didn't work well. Took it to the shop and had a new heater core installed. It worked fine for the rest of the winter. Yesterday, it was rainy and cool out so we turned the heater on for the first time. NO HEAT. At all. Blows cold. Not sure at all what the problem is. Any suggestions?