What looked like a standard central-air setup in one Arizona apartment turned into a mystery when a renter traced a foul smell to a hidden HVAC unit that was nearly impossible to reach up a shaft.
By removing a floor-level vent beneath the thermostat and taking a photo upward, the tenant came to suspect that the "central AC" was actually an air handler hidden inside a narrow vertical chase.
Here's what to know
The renter took to Reddit's r/HVACAdvice forum to see if anyone knew how they could change the AC unit's filter when it was located up the shaft.
In the post on Reddit, the renter said their lease makes management responsible for replacing the filter, while the tenant is supposed to report its condition.
The difficulty, though, is that the suspected access point is a 23-inch-by-12-inch vent the renter called "the only entrance that appears to provide access to the AC unit," making it unclear how the filter could be reached at all.
The tenant added that the opening "sucks air in when the AC is working," which further suggested it is part of the return-air path, and said the filter may be somewhere behind a vent too small for a person to enter.
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The post also described an odor that becomes noticeable after the system has run for a long time: "If the AC has been turned on for a long time and I enter the apartment after staying out for a while, there is a smell as if a long dead animal carcass is hidden somewhere in the apartment."
One commenter joked, "Hire an 8-year-old chimney cleaner. Isn't that how they did it back in the day?" Another suggested, "Don't touch it. Get the owner out there. I would be very surprised if that has anything to do with your HVAC."
A third commenter wrote, "Yeah, that's almost certainly a rooftop package unit using the old chimney chase as a return air path, filter's gonna be up top in the unit itself not down in the shaft. Call the office and ask specifically about roof access for filter changes, don't try to climb into that vent yourself."
More background
Hidden or awkwardly placed air handlers are not uncommon in apartment buildings, especially where space is tight and units are stacked close together. Limited access can make routine upkeep much harder, even though components such as filters need regular attention to keep air flowing properly.
A dirty filter can force an HVAC system to work harder, raising cooling costs and increasing wear on the equipment.
The smell described in the post suggests the issue may go beyond the filter itself and require an inspection by a maintenance worker.
What can be done?
Documentation can strengthen a maintenance request. Photos of the vent opening, notes about when the odor appears, and a copy of the lease language can help.
A specific request to inspect the filter and confirm where the air handler is located may be more useful than a general complaint that the AC smells bad.
Trying to squeeze into a return opening or remove concealed panels without approval is generally not a good idea, especially in a multi-unit building where ductwork, wiring, and neighboring systems may be packed into the same chase. A professional visit is safer and more likely to resolve the problem.
If management does not respond, keeping a written record of requests can help.
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