99 accord LX seems of late air will continue to blow thru the vents even when switch is off ...seems as if air blows thru only while driving / moving down the road so I figure something isn't closing .not at all sure where to look...is the system vacuum or mechanical ? the fan does shut off but air will still come thru while driving

 

https://hond-tech.com/how-tos/honda-...s-stuck-376748 very informative for your post.