5700XE HVAC Question

I have a suspicion my HVAC is stuck on recirculating air no matter what setting. It’s 15F outside and when I turn engine off and heater to minimum it keeps blowing air with ambient cabin temperature rather than pulling in cool outside air. How do I check the flapper/actuator? I took the glovebox and lower plastic cover and can see the blower motor and filters but are not sure where the outside air duct is?

 

I see the intake inside the cabin and can feel the air being pulled in, but where is the outside intake?

 

Are you talking about inside the cabin near the passenger door? I’m trying to figure out how the outside air supposed to come in to blower box.