DIAGNOSIS: The unit isn't properly exhausting hot air, or the refrigerant circuit has an issue. The most common culprit is an incomplete seal on the window vent kit.
FIX: Seal the window vent kit completely. Check every inch. The foam panels must fill all gaps. The exhaust hose must be fully snapped into both the unit and the window bracket, with the inner flap opening freely. A tiny gap here pulls in hot attic or wall air, killing cooling.
IF THAT DIDN'T WORK: The condensate reservoir might be full, triggering an auto-shutoff to prevent overflow. Unplug, move the unit, and check the drain plug at the back-bottom. If water comes out, empty it completely.
HEADS UP: These units are inherently less efficient than window ACs because the entire hot side (compressor, condenser) is inside your room. A perfect seal on the single-hose vent is non-negotiable for it to work at all.