Why is my Honeywell MN10CESWW suddenly filling up with water every hour?

The build-up of gunk and dust on your condenser coils is 100% the reason you're suddenly having to drain the tank. These Honeywell units use a self-evaporating system where a slinger fan picks up the condensate and throws it against the hot coils to turn it into vapor, which then goes out the exhaust. When those coils are matted with dust, the water can't evaporate efficiently, so it just pools in the bottom tray until the float switch kills the compressor.

You need to give those coils a deep clean with a soft-bristle brush and a vacuum, or even some specialized coil cleaner if the grime is oily. Just be careful not to bend the aluminum fins. Once the airflow is restored, the unit should go back to being maintenance-free regarding the water, assuming your humidity levels haven't spiked recently. The weird temperature readings are a separate but related headache. That 50-degree reading usually means the **thermistor**—the little copper-capped sensor—has either fallen out of its clip and is touching the freezing cold evaporator coils, or it's failing entirely. If it's touching the coils, it thinks the room is freezing and shuts the compressor off to prevent icing, leaving you with just the fan blowing warm air while the exhaust stays hot for a bit.

While you have the casing off, look for a small wire with a black or copper tip located near the front evaporator coils. It should be suspended in the airflow, not touching the metal fins. If it's positioned correctly but still reading 20 degrees off, the sensor is likely shot and needs a replacement. But definitely start with the cleaning first; if the unit is struggling to move air, it creates all sorts of thermal feedback loops that confuse the control board.

Spot on. I had the exact same issue with my MN10CESWW last summer. One thing I'd add is to check the drain port's internal rubber plug while you're cleaning out that gunk. Sometimes those can get a slime buildup that creates a vacuum seal, preventing the water from even reaching the slinger fan properly. If you find alot of 'bio-slime' in the tray, it can acutally coat the sensor tip too, giving those wonky readings. Give that little copper bulb a quick wipe with a cotton swab and some rubbing alcohol to make sure it's getting an accurate ambient air reading once it's back in its clip.

If cleaning that Honeywell doesn't fix the sensor issues, honestly don't waste more time on it. I switched over to the Midea Duo 14,000 BTU unit and it's a total game changer compared to those older single-hose designs. The dual-hose-in-hose setup makes it way more efficient and I've never had a drainage issue even in high humidity. If you're tired of the 'bio-slime' and sensor failures, just grab a Midea Duo and save yourself the headache. It’s significantly quieter too.

Since you're allready digging around in there, check if the float switch is stuck. If it's covered in gunk, it'll trigger the shutoff even if it's not totally overflowing. I'd also grab some of those Algae strips or pan tablets. Just drop one in the tray after you've cleaned it out. It stops that slime from growing back and keeps the drain clear so the slinger fan can acutally do its job. Works way better than just scrubbing it and hoping the mold stays away.

I had this exact mess with my Honeywell last July. The cleaning helps, but I found that even after scrubbing, my unit kept acting up untill I used a can of compressed air on the control board connections. Dust gets in behind the display panel and causes those ghost temperture readings. Also, if you're sick of the bucket brigade, I ended up just propping mine up on a couple of 2x4s and running a vinyl tube from the middle drain straight out a hole in the floor. Never had to worry about the slinger fan or the 'tank full' light again.

Quick update — I cleaned the coils and found that slime buildup near the slinger fan like you guys mentioned. It’s draining much better now, but the display still says it’s 52 degrees in here. Since I’ve allready got the casing off to check the float switch, does anyone know exactly where the temperature sensor is located? I'm wondering if it's just caked in dust too.