While having my instrument cluster off, I took a look at the vacuum actuators that are behind there, controlling the defroster and floor heaters. These actuators are hardly moving at all when I hit the three-way buttons. I put my finger on them and can feel that they are trying to move, but they just don't have enough power to move the levers. Is this because they are old and bad, or is it more probably a vacuum leak somewhere else down the line?

Also, what is the worst that can come of these actuators not working? If all it means is that the defrosters will be on all the time, that's fine with me because I don't live in a very cold place and never need the full power of the heaters. But if a problem with this vacuum system will mean a weak fuel-air mixture, then I ought to fix it whatever it is, no?