Hi, i changed my heater core some weeks ago and now all seems fine but something happens, i dont have cold air , i switch the temperature regulator but the air comes always hot , the funny is that when i switch the temperature regulator whit my engine stoped i can hear a noise inside dash , so it seems the door that control temperature inside heater core box is working so cant undestand why i cant have cold air , im almost pretty sure i install everithing rigth so dont know whats the issue here