AC Box Rebuild-Missing Flapper Door

I believe Dana is correct. That "switch" i think goes closer to lower drivers side. I could be wrong tho. I belive it acts like a "thermostat"??
Not sure if you have installed the spring clips around the perimeter yet? Those things are DAMN TIGHT!!
Before we reinstalled ours i took some of the tension outta them. They will crack the 60 yr old casing very easily.