To clarify, there are 2 switches, both in the same room. The obvious one, and a hidden one to it's right, behind all the machinery. These open a door to your left when using the vent to enter the switch room. There is also another switch that opens the door to the hallway shown in the pic, allowing easier access to the rafters. Just need 1 chair to reach it.

For those wondering where the hidden switch is (which opens the secret door), world location , map location

There are hidden switches in the connected rooms accessible via vent to the south, across from the 2F walkway that open this passage