Just in case Trojan wasn't quite clear on the area you're talking about, I'll go ahead and elaborate a bit. I got stuck there for a while as well, and I know it can be quite frustrating.
From what I gather in your post, you've gone into that second side room and are wondering how in the hell you're supposed to get at that switch behind the glass wall. Truth be told, I have no idea what that switch does. However, in that very room, there's an isolated crate on the back wall that you can pull to reveal a small crawl-space. The corridor beyond leads to your ultimate destination, but unfortunately, there's a cart blocking the way. You can't push it out of the way until you move the cart behind it.
Getting at this second cart isn't quite as simple. Head back to the main room. In it, there are four garbage compactors, each with its own drop point for the garbage. All but one of these compactors will have a cart full of trash sitting directly beneath the output valve. You have to find the compactor that doesn't have a garbage cart sitting beneath the output and jump up into it. Wait for the crusher to rise and run through to the other side; use Speed if you can't make it. The path from here is pretty straightforward; find your way to the corridor with the carts, pull the one you find, and then head back to the room with the glass wall. Return to the corridor, push the cart, and head into passage on your right. Voila!