I have a 1998 ford Taurus with no heat. Heater core is good, I flushed out the heater core, flushed out the radiator, new heater hoses, new thermostat, made sure there's antifreeze in it. Still no heat just cold air

often a stuck shut blend door inside the dash, a NO FUN job.

Yes I checked that! The blend door is wide open. It still blows cold air, it feels like the AC is on