Is my ancient window AC unit a lost cause or just disgusting?

Sludge on the fins is definitely what's killing your cooling power. AC units work by pulling heat out of the air trough those metal coils, and if they're caked in a thick layer of biofilm or slime, the air can't actualy touch the metal. It is like trying to cool off by blowing a fan through a thick wool blanket. That standing water in the bottom is just concentrated dust and humidity that turned into a petri dish because the drain holes are probaly plugged with more of that gunk.

You can absolutely save this thing with about an hour of work and some cheap supplies. Pull the whole chassis out of the outer metal sleeve if your model allows it—most old window units slide right out. Take it out to the driveway and hit the coils with a mix of **dish soap** and warm water in a spray bottle. Let it sit for ten minutes, then use a soft-bristled brush to gently scrub in the direction of the fins. Do not go side-to-side or you will bend the aluminum and block the air even worse. The shot coolant theory is usually the last thing to worry about. These systems are hermetically sealed, so unless there is a physical puncture in the copper lines, the refrigerant is still in there. The heat exchange process is just physically blocked. Once you spray it out with a garden hose—be careful not to soak the control board or the motor directly—and clear those drain ports in the back tray, it will probably start blowing ice-cold again. If you clean it thoroughly and it still doesn't cool, then it belongs in the scrap heap. But honestly, those old units from the 90s were built like tanks. They use more electricity than a modern inverter model, but they usually last forever if you keep the coils clear. Just make sure you let it dry out in the sun for a full day before you plug it back in to be safe.

I've got a similar crusty unit in my garage and I'm wondering about those drain holes. Are they usually on the very back edge or hidden underneath? My pan is so full of gunk I can't even see the bottom to find the exit point.

Also, is there a specific type of brush that works best? I have an old dish brush but the bristles feel a bit stiff and I'm terrified of mangling those little metal fins. I'd way rather spend an hour scrubbing than $300 on a new machine if this actualy works.

If you're worried about the fins, skip the dish brush. Go grab a cheap 2-inch paintbrush from the hardware store. The soft bristles are perfect for getting into those gaps without folding the aluminum over like a pancake. Check the back corners for those drain holes; sometimes they're just tiny stamped divots that get plugged by a single leaf. Also, keep an eye out for a 'slinger ring' on the fan blade—those old units acutally use a bit of that water to splash onto the condenser coils to help with cooling, but you still want the excess to drain so it doesn't turn into a biohazard.

Keep an eye out for some foaming coil cleaner at the hardware store if the dish soap doesn't quite cut trough that 90s grease. The foam expands and pushes the gunk out from between the fins where a brush can't reach. Also, be careful when you're sliding that chassis out—those old metal units are surprisingly heavy and can slice your hand if you grab a sharp edge.

If it still smells funky after cleaning, a tiny splash of white vinegar in the base pan can kill off any leftover spores. Just don't overdo it or your whole room will smell like a pickle for a week.