I just bought a used 2003 Neon SXT. Everything works fine except there is no heat coming out of the inside vents. All the fluid levels are correct and the right mix, the inside vent cables are attached, the car runs in the proper temp range, I switched the supply and return lines to flush the heater core. The supply and return lines are cool to the touch and there is still no heat coming out of the vents. Dose this mean the heater core is bad or is there another possible problem?