try replacing the thermostat. It is probably the easiest fix, as well as cheapest.
Coolent leaks from pasenger side of engine.
It may have a bad heater core.
Sounds like your heater hose going to the heater core is stopped up some where along the way, Or your thermostat is broken. Otherwise if there is hot water getting to the core then it WILL blow warm air.
You need to change your thermostat in the car.
Most likely a replacement heater core
this is not an answer just an update. coolant is filled
It is because your heater is having to heat up so its blowing cold air out while its heating up.This means your heater is not very efficient and it needs to be checked.
check your coolant level. if its full, might be a plugged heater core.
is the blower motor running? or is it just not blowing hot air?
Is it not hot? Not blowing? Leaking coolant? Need more info to help you.
Check the temperature control cable
heater core plugged or air locked check to see if hoses going to heater core are hot