my guess is the vaccume acually is the force that opens them... instead of some sort of signal... vaccume does all kinds of cool stuff.. on my cougar i had a problem with my panel/floor HVAC function.. it wouldnt change from panel... took me all day to figure out i forgot to plug the vacume line back into the manifold.. i had no idea that the HVAC acuatator would be vaccume controled... heh.. guess im a bit naive bout some things.