Have a 2001 mitsubishi galant heater will not work have new thermastat and coil still blows cold air what could this be

There is probably some kind of damper that opens and closes under the dash that allows the air from the blower to be blow across the heater core under the dash. Sometimes these are controlled electronically or by vacuum tubes. Look underneath the dash and look for small vacuum hoses that might be dangling loose or possible little wire cables that might have come off the sides.
Possibly check Haynes Manuals (www.haynes.com) to learn how to change a Heater Control Valve.

do you have a guage to check the low side pressure? if the low side pressure is less than 20 psi then you could have a bad expansion valve that is not letting the freon circulate. also check the controls to see if the heater works all the time. the air temp door may not be moving to the cold position.

Flush coolant system out first with prestone or peak coolant flush if problem still exist replace heater core.

heater core

This could be that the actuator that opens the door in the heater is dead.. or the actual heater-core is bad. Which is costly and expensive.

try to back flush the heater core. and if that dont work check the blend door it see if it is working.

try driving around for almost 4 months and the damn thing wont blow cold. try spending thousands of dollars and it still being broken. and trying driving in florida in upwards 115 degrees with no cold ac everyday. you only have to wait 30 minutes? count yourself lucky!

This may be a solution:
I had a similar problem at the beginning of this winter.
My heater was blowing cold air.

My solution:
Heater Temperature control cable, about $10 from dealer
Install, about $70, at my local Firestone

before u add water in ur radiator make sure u start ur engine and remove ur radiator cap and pour water to it when u see there is no more air in ur radiator u can close it and it will work good