How do I properly dismantle and store a window unit in an older building?

When dealing with those older, heavier window units in tight spaces, the priority is controlled disassembly and proper drainage, since a sudden drop or yank is what usually compromises the internal plastic clips. Start by ensuring the power is completely cut off at the breaker. You want to isolate the unit before you even begin unscrewing the mounting hardware. Most units have a basic circuit, and those brackets are often tightened into the brick or framing itself, so loosening them in stages helps manage the weight shift. Don't try to haul the entire block off the sill; loosen the screws securing the housing first, leaving the primary bracket still attached to the masonry untill the last moment. For the actual lift and transport in a narrow opening, a proper two-person lift is usually essential, especally given how much they weigh. If you can, use a flat dolly or a heavy furniture mover with straps to distribute the weight and manage the descent from the sill. Never try to just drop it down, as that internal housing can shatter. Regarding your worry about moisture, this is more important than the removal process itself. Before storage, you have to ensure the condenser and evaporator coils are completely dry. Run the unit in fan-only mode for several hours just to circulate air and let the remaining moisture evaporate. Then, wipe down all accessible metal surfaces, particularly the coil fins. If you leave damp components inside a sealed unit, you’re inviting mold and corrosion that will eventually ruin the heat exchanger.

Once the unit is off and dry, if you are storing it vertically, make sure the drainage pan is as clear as possible. If you're worried about the brick or structural damage when you move it, taking photos of the mounting points before you start is a smart way to document the condition of the opening for later reference.

I totally agree with the advice about running the unit in fan mode for several hours. It is crucial to get all that trapped condensation out or you are just setting yourself up for mold issues later. My expirience shows that when I was removing mine last season, I noticed the internal drainage cap was an easy pull-off. I disconnected that and physically scooped out the water that had collected in the pan. Wiping down the fins after that gave me alot more peace of mind about storing it correctly.

I disagree that running the unit on fan mode for hours is the primary way to handle trapped moisture. While that's common advice, I think it's mostly a waste of electricity when you could just open the access panels. Most of the water collects right in the fins, and the only way to get it out completley is physical access. If you have the tools, taking those outer panels off and wiping the coils down manually is way more effective than letting a slow fan circulate air until you're ready to store it.

I'm dealing with a similar heavy older unit, but ours is mounted in a double-hung window rather than a narrow opening. The advice about isolating the unit before starting is realy helpful. I'm a little unsure about how to manage the weight when detaching it from the sill, becuase if I pull it straight out, it feels like the bracket might just rip out of the wood itself. I guess I need to figure out if I shold try and support the unit while I disconnect the frame first.

Update: I finally got around to taking it down. I decided to try opening the access panels first instead of running it on the fan for hours like some suggested. I found that draining the condensation directly out of the fins was much faster and didn't waste a lot of electricity. It made the whole removal process much cleaner, so the unit looks good for next year.