Why does heater blow cool air?
Old trick with any car ,firstly drain the antifreeze out then refit the bottom hose ,get a plastic bucket and add about a cupfull of caustic soda ,add hot water being usual carefull about this then when the caustic has disolved you add this to the radiator ,then providing the level is ok you refit the rad cap and run engine ,time ? depends say a half hour drive around town ,then let engine cool ,remove the bottom hose to drain being carefull as well whilst doing this .then remove the rad cap and flush it through ,then refit the bottom hose and remove a heater hose ,both it access allows then flush back through the heater hose ,both ways if you can both heater hoses off ,then refit one heater hose and let it back flush out through the rad cap then reverse this flow ,and if it all comes out nice and brown then clears you know your heater will work ,now drive car around with the water in for 5 mins then drain via bottom hose and then after fitting the bottom hose refill with antifreeze 50% min ,even in a frost free climate as the antifreeze is a anti corrosion agent as well .