Spent the weekend cleaning out my Midea Duo and learned a lot

I ran into the exact same issue with my 14,000 BTU unit last summer after noticing a faint swampy smell every time the compressor kicked on. Living in a humid climate, I realized that the "self-evaporating" feature just can't keep up when the dew point is high. Even though the manual says draining is only for "Dry" mode, I found that pulling the bottom plug every Sunday usally results in about two cups of nasty, stagnant water coming out.

To fix the buildup on the blower wheel, I ended up using a long-reach brush and some Concrobium spray. Now, I make it a habit to run the unit in "Fan Only" mode at high speed for at least 45 minutes before I shut it down for the day. It’s annoying to remember, but it’s the only way to get that internal moisture off the blades so the mold doesn't have a wet surface to grab onto. I also tilted my unit slightly backward by putting a thin piece of plywood under the front feet, wich helps the water migrate toward the drain plug instead of just pooling under the fan.

I’ve had two Midea Duos running for three seasons in a coastal area, and I’ve found that the shutdown routine is what actualy makes or breaks the mold situation. If you just hit the power button when the room is cool, that blower wheel stays damp in a dark, sealed cavity—perfect for growth. The moisture isn't just in the pan; it's clinging to the plastic fins of the wheel itself.

I started using a smart home routine to run the "Fan Only" mode for at least 45 minutes every evening before the unit fully shuts down. It helps dry out the internal components significantly. I also took the extra step of tilting my unit slightly backward by putting half-inch plastic shims under the front feet. This forces the condensation toward the rear of the pan where the slinger ring can actually reach it, rather than letting it pool near the front vent area.

Even with those tweaks, these units are definatly high-maintanence. I spray a bit of Nu-Calgon Evap Power into the intake once a month during the peak of July. It seems to break down that biofilm before it gets fuzzy. It’s a bit of a hassle compared to a standard window unit, but it’s kept my blower wheel looking clean without needing a full teardown.

This is honestly kind of terrifying to read becuase I have this exact model and I've never opened it up. I’m not very handy, so the idea of 'tearing the chassis apart' sounds like I'd just break it. Does the mold always smell? I haven't noticed a 'swampy' scent yet, but now I'm paranoid that I'm breathing in gross stuff without knowing. Also, for the tilting trick with the plywood, does that mess with the internal sensors or cause any leaks out the front? I relly don't know much about how the drainage flow is supposed to work.

Ugh, that’s my biggest gripe with portables. I've found that keeping the filters super clean helps more than you'd think. If they’re even a bit dusty, the airflow drops, and that blower wheel stays wet way longer. I actually rigged up a small shop vac with a narrow attachment to suck out the drain port instead of just letting it drip. It gets way more of that sludge out than gravity alone. If you're seeing standing water, the 'self-evaporating' pump might be clogged with gunk too. Might be worth poking a pipe cleaner in there.

I'm curious if you've ruled out the humidity levels in the room before you blame the chassis design? If the ambient air is already at 70% or higher, no amount of self-evaporation is going to keep up. I've had mine for two years and it's bone dry inside, but I keep a dehumidifier running in the basement nearby. I'm also wondering if you checked your window seal? If you're leaking hot, moist air back into the intake, you're basically creating a localized tropical climate inside the unit that it wasn't built to process.