Hi Kevin and welcome to the forum

The actuator motor is located just above the hump in the floor. You get at it by removing the black plastic trim piece in between the floor and the dash. it just has a couple screws or pins that hold it on. I think I'd remove the actuator and take a look to make sure the blend door isnt broken or binding. Did you find the Explorer blend door fix in the Explorer forum?
As for the A/C problem I'm really not sure. The vacuum motors could be affected by the drop in vacuum when you accelerate hard if there is a leak in the system. However, the vacuum operated doors only control the air distribution and not the temperature.
I'll try to get some more info for you here.