No heat

I had heater core & thermostat replaced & i'm not getting heat. Someone said it could be a air lock. Any idea how I can fix it?

Do not know if you still have this issue, but, most of these engines had a little air bleed nut near the front of the engine (at least on 6 cylinders). It was at the end of the long black metal line in front. Run the engine and open this while idleing until antifreeze comes out. Wait a few seconds and do it again. Squeeze the top hose to force air out, top off radiator and loosen the screw once more. You may also have a problem where the controls are not working due to a vacuum leak in engine of the hoses under the dash. These controls rely on vacuum to work. Check all vacuum hoses.