No vent control on Ford Explorer

You will need to gain access to the air box and vacuum controls behind and under the dash. Once you have this access, cycle the controls slowly from defrost through heater and vents, listening for a vacuum leak. With the engine off, cycle the controls to verify that all are able to move freely and through their full range of motion. Verify that the vacuum line(s) from the engine to the vent controls is supplied with vacuum and has no leaks.