i have a 1993 f150. earlier in the winter i could not get my heat to come out of my vents, found a disconected vac line, plugged it back into this huge ball looking thing, that has 2 mounting tabs on the bottom and 1 hole for a vac line. it fixed my issue and i can switch between all my settings just fine. i havent noticed til today that even with my hvac control set to the off position, its still blowing air out of the defrost vent. i searched our forums and couldnt really find anything. how do i go about fixing this? thanks guys!