Why is my car's heater blowing cold air?

A car heater is like a small radiator inside a box. If your engine is warmed up hot water should flow through the heater core and heat the air. Under the hood you should see two black 1 in. hoses going into the firewall. They both should be hot or at least quite warm. If one or both hoses are cold your valve is not opening. Some cars use mechanical cables to open the valve but more and more car use vacuum from the engine. Vac switches can go bad and leak, not having enough energy to open the valve. If this is your situation you may need professional help. I worked on a Pontiac once and the first step was to jack the car and remove the right front wheel and inner fender. What a pain.

Why is my car's heater blowing cold air?
Check your anti freeze level it is probably low

Heater blows cold air in a 2007 Ford Explorer everything seems to be working but the heater know controller makes a clicking sound.

Heater blows air in a 2007 Ford Explorer and the heater control knob makes a clicking sound.