Heater problem
2000 Chrysler Sebring 6 cyl Front Wheel Drive Automatic 121000 miles

I was given this car and it has no heat. I changed the thermostate, flused all the rust out of the cooling system, R&R and cleaned the resev. There was still not heat. The system was so dirty, I thought the heater core may have been restricted. So I replaced the heater core. Still have no heat. The heater doors are operating properly. It almost seems like there is air in the system. Any suggestions

Pull rad cap jack up front car run fill as neseccary. Replace cap let cool then run again adding to resevior as needed.