While servicing the air filters on the OTR air conditioner, I noticed that there is what appears to be a flow regulator flap valve in the air inlet tube.

Is that, in fact, what it is? Kinda looks like the type of flow regulator found in home forced air systems, with a lever on the right side.

Is there a "normal" position for this flap? Looks like it could be "locked" into a stationary position. Or, is it supposed to be able to open/close freely?

Should it be "locked" in the open or closed position?

Comments/advice/observations would be appreciated