The answer to 'furnace blowing cold air' is that the most common causes are a malfunctioning thermostat, clogged air filters, or a problem with the furnace itself. This can indicate issues like a broken heating element, a problem with the blower motor, or a refrigerant leak.
Some common symptoms include the furnace running continuously but not heating the home, cold air coming from the vents, and the furnace shutting off unexpectedly. Potential solutions depend on the specific issue, but may include replacing the thermostat, cleaning or replacing the air filters, or calling in a professional HVAC technician to diagnose and repair the furnace.