Mercury Grand Marquis 2008 no heat in cabin

there is a heater core in the car its behind the glove box. you said you checked the vacuum door the temperature blend door is electric you must have been looking at a different door. the temperature blend door is on top of the heater core housing you can see it if you take the glove box out. most likely what you have is a bad actuator its stuck on cold. you can see the part where it goes into the box. move the temp on the consoule and see if it moves. ive seen alot of these go bad and they will usually stick one way or another. bad part is the dash needs to be removed to replace it.