Generally, heater-A/C systems control air flow with dampers - little doors that direct the air flow through either the heater core or the A/C core and then to wherever you want it to go in the cabin. These are controlled either mechanically (levers, cables etc.), pneumatically (vacuum tubes), or possibly electrically with servo motors.
It sounds like your dampers are not functioning properly. My guess is they are vacuum operated and you have a vacuum leak.

Replaced the thermostat and bled the system. The heater core is plenty hot, Just will not blow any heat. Also the a/c button is flashing green and there is only one direction (floor) that the air blows. When I change the direction, defrost, vents and floor, it only blows out the floor vents. Have checked all the fuses.