Mazda Millenia Heater Not Working

Heat Won't Work It Blows Just Regular Air A Friend Says That I Have To Replace The Unit That Closes And Opens The Air Vent System How Do I...

Had Heat A Month Ago Coolant Level Find Doesn't Over Heat.is This Problem The Heater Control Valve

When The Setting Is On Heat And Temp Up To 90 The Air Blowing Out Is Not Hot. Could That Be A Fuse Problem? It Did The Same Thing Last Year...