Not sure why but I turned blower fan motor on high the other day. Almost chocked on all the dirt that blew out. 2 Days later, after 310 miles (10-15 on gravel ) tried fan again. More dirt came out. Asked Ford service, there is no cabin filter, he has heard nothing so far about dirt entering cabin through heater fan. Has anyone else experienced this? Good thing my wife wasn't in there at the time. 7000 miles on new truck shouldn't have that much dirt in heater/AC blower.