when i run heat it only blows cold air. new thermostat and bled system from blee

Could be a multitude of things. Heater core could be plugged, heater control valve non op, or just the blend air doors malfunctioning.

Maybe, What engine¿?¿?!!!! IF 4.3 what bleeder screw?? Give more info. and we can too. Hey that rhymes, forget answering questions, i am going to try poetry!