There is a door inside the plenum that controls the air flow. It is called the mode selector. It is run by vacuum. Looks like this: https://www.carid.com/2011-ford-f-150-air-conditioning-heating-parts/motorcraft-hvac-recirculation-door-actuator-71995542.html IT may have a leak in the hose, the unit itself, the door is stuck. something could be jamming the door that fell down the vents, the control rod from the door could be broken or loose.
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Watch the video please. DIY Ford F150 Stuck Heater Hvac Vents Repair
There is a door inside the plenum that controls the air flow. It is called the mode selector. It is run by vacuum. Looks like this: https://www.carid.com/2011-ford-f-150-air-conditioning-heating-parts/motorcraft-hvac-recirculation-door-actuator-71995542.html
IT may have a leak in the hose, the unit itself, the door is stuck. something could be jamming the door that fell down the vents, the control rod from the door could be broken or loose.