Why is my heater blowing cold air?

Hello, it sounds like your engine is not reaching proper operating temperature. There are several things that can cause poor heat inside the car, but that's a good place to start. A monitor is needed to check engine coolant temperature. This will show if the thermostat is staying stuck open or not --- the engine will never attain temperatures above 190 degrees or so unless stressed a bit, such as while the engine revs at higher speeds creating more heat. Naturally there are other reasons you could have no heat, but start here.