The answer to 'why is my ductwork blowing cold air' is that there is likely an issue with your HVAC system. This could be caused by a problem with the furnace or air conditioner, such as a malfunctioning thermostat, a refrigerant leak, or a blocked air filter. It could also be due to ductwork issues like leaks, disconnections, or insufficient insulation.
If your ductwork is blowing cold air, it's important to have a professional HVAC technician inspect your system to diagnose and fix the underlying problem. Trying to repair the ductwork or HVAC system yourself without the proper knowledge and tools can be dangerous and may even make the issue worse.