i replace thermostat it stall blow cold air

 

Check you radiator fluid level. That is what is used to heat the heater core and without enough fluid it can't heat the air.

 

also check the valve that operates the heater it might be stuck

 

i dont know what type of vehicle you have as you geniously decided not to tell anyone. But I had a probelm before with a fuel injected vehicle that was a 92. either the antifreeze was low or the oil was low. and the fact it would not blow hot air was a programed deterent so you would check on those things... check them out and if not i'd go for the heater core.