Symptoms
- Musty, sour, or moldy smell when the unit starts
- Smell strongest right after turning it on
- Visible grime in the water tank
- Smell fades somewhat as it runs
Likely causes
- CommonStanding water or mold in the internal tankWater that sits for days between drainings grows odor-causing bacteria and mold.
- CommonDirty or mildewed filterDust mixed with moisture on the filter is a common mold spot.
- PossibleMold on the internal coilCondensation on the coil that doesn't fully drain can support mold growth.
- PossibleUnit stored for a season with moisture left insideOff-season storage without drying it out first invites mold.
What to do
- Unplug the unit, drain the internal tank completely, and rinse it out with warm water and a little dish soap.
- Remove the filter and wash it with warm soapy water, then let it dry fully before reinstalling.
- If the manual allows access to the coil, spray it with a coil cleaner or a diluted vinegar solution and let it sit briefly before wiping.
- Run the unit in fan-only mode for 30–60 minutes with the tank empty to help dry out the interior.
- Empty the tank more frequently, or set up continuous drainage, so water doesn't sit for long periods.
- At the end of the season, dry the unit out fully with fan-only mode before storing it.
Tools and parts
- Mild dish soap
- Soft brush
- White vinegar (optional)
Portable AC replacement filterSearch: “portable air conditioner filter”
When to call a pro
Call an appliance technician if the smell persists after cleaning the tank, filter, and accessible coil, since mold may be deeper inside the unit.
Safety
Generally low risk
Generally low risk for a careful person. Stop if anything looks different from what this guide describes.