One thing I would do is remove the heater hoses from the heater core tubes at the firewall.Use a garden hose to spray water through the larger of the two tubes and see if rusty or dirty water comes out.If so,continue spraying water until it turns clear then switch to the smaller tube and repeat the process.When dirty water comes out,its usually a sign that the heater core was clogged and a clogged core won't allow coolant to flow through it properly especially since coolant is thicker than water and 50-70% of what's in the system is coolant vs water.Reinstall the hoses and test the heater.Another cause for no heat is a bad thermostat,especially if the thermostat is stuck open.A defective thermostat never allows the engine to heat up properly so hot air is not present.The thermostat can also stick closed and this will cause cool or luke warm air to come out of the vents.The engine normally overheats when the thermostat sticks closed though.Look for vacuum hoses running along thefirewall

Thermostat stuck open or heater core restricted

a plugged heater core

heater control valve

I own a 2003 Chevy Malibu. I get plenty of cold air and when i switch the control to heat it keeps throwing cold air.

So far I have-

1.)Checked coolant and it has plenty.

2.) i have replaced the temp blend door actuator and still doesn't work.

What else could it be?