Subaru Forester A/C problems

That should have read A/C, darn autocorrect shirt...

Vents open?

If mechanical (likely), it's usually the actuator door ROD that disconnects near the passenger's left knee wall...sometimes from an errant kick. Look under there and if you can find a loose metal rod end find the clip it anchors too and snap it back together. If the vent functions cycle without AC normally then the issue is elsewhere.