Where is the intake vent on this industrial fabric-wrapped AC system?

The white fabric part you're seeing is called a **duct sock** or fabric ducting. It's used almost exclusively for supply air, meaning that's where the cold air comes out, not where it goes in. The fabric is porous so it lets the air bleed out evenly across the whole length of the pipe rather than just blasting it out of a few metal grilles. It's a solid setup for big open workspaces becuase it prevents those annoying cold spots you get with standard registers. As for the intake, that larger rectangular box is your return air plenum. If you look at the top or back of it, there might be a wire mesh screen, but you probably won't find a filter rack anywhere inside the building. In these industrial setups, the ductwork ussually goes straight up trough the roof to a **rooftop unit** (RTU). That's where all the actual mechanical work happens and where the air gets pulled back in. You’re going to need to get on the roof to find those filters. Look for a large metal cabinet sitting directly above where those ducts go through the ceiling. There will be removable panels on the side of that unit—usually held on by latches or a few hex-head screws—and that's where the filter bank lives. Since you mentioned it’s never been cleaned, those filters are probably choked with dust and might even be collapsing inward from the static pressure.

While you're up there, check the evaporator coil and the tension on the blower motor belt. If the filters haven't been touched in years, the coil is likely caked in grime, wich will kill your cooling efficiency once the summer humidity hits. Just make sure you kill the power at the local disconnect box near the unit before you start poking around inside the cabinet. If you can't get on the roof safely, you'll need to call a tech, because there is nothing you can do from the floor level to fix a neglected system like that.

So that white fabric is actually letting the air out? I honestly thougth it was just insulation wrapped around a regular pipe to keep it cold. Now that you mention the roof, I'm a bit nervous. Our ladder is barely tall enough to reach the ceiling, let alone the actual roof. Is it common for these RTUs to have some kind of warning light or a pressure gauge inside the building so we know when the filters are toast? I'd hate to hire a tech just to find out everythign is fine, but I also don't want to bake in July.

Most basic commercial setups won't have a gauge inside unless someone paid extra for a Magnahelic or a remote monitoring system. If it’s an older warehouse, you’re flying blind from the floor. One quick trick though: look at the duct sock when the air kicks on. If it stays limp or takes forever to fully inflate, your filters are definitely restricted or the blower belt is slipping.

Also, listen for a high-pitched whistling near the return plenum. That’s ussually air trying to bypass a clogged filter. If you can’t get on the roof, you're better off hiring a pro. Those RTUs are heavy-duty and can be dangerous if you don't know how to check the refrigerant charge or the contactors.

Keep an eye on the color of that white fabric. If you start seeing dark gray streaks or "dust ghosting" along the length of the sock, it’s a huge red flag. That usually means the filters are so packed that air is forcing dust past the seals and into the supply. At that point, the sock itself is acting like the filter, wich will eventually clog the fabric pores and kill your airflow entirely. If you're worried about the ladder situation, ask an HVAC tech to install a simple differential pressure switch next time they're up there. It’s a cheap way to wire a "check filter" light somewhere you can actually see it from the floor.