To stop the humidity buildup in the closet, you need to address the stagnant air. An interior wall closet with a constantly running AC can still be a humidity trap. The best immediate action is to install a battery-operated dehumidifier unit or moisture absorber like silica gel packs inside the closet. For a more permanent solution, leave the closet doors ajar periodically to allow conditioned air to circulate. If the problem persists, the root cause could be a lack of adequate ventilation in the room itself or even a slight negative air pressure difference.

In severe or recurring cases, a professional inspection with moisture meters can identify hidden condensation points or underlying leaks that aren’t visible. They can provide data-driven solutions tailored to your specific apartment’s air balance.