if you have found the yellow vent switch, and you know where the vent is, go to the vent. if you come in over the curved path, it will be on your right, if you come in the other way, it will be on your left. look through the goggles back in the way you came if you went over the curved path or towards that entrance. there will be a frozen crate up on the wall. shoot it.

When you have found the yellow vent switch, go to the ice above that switch.
Walk back towards the beginning of Snowy mountain.
Go to the first yellow eco vent you see, look behind you, there you see a crate in the wall, shoot that crate.

its stickin out of a wall of ice in a cave tunnel and you have to unlock the vents of yellow eco and fill up and shoot it and your finished.