A portable air conditioner is a dehumidifier, dust filter and refrigerator rolled into one box — which means dust and moisture are constantly trying to shorten its life. The maintenance is genuinely easy; it just has to actually happen.
Monthly during the season: the filter
Slide out the washable filter (usually a rear panel), rinse under the tap, air-dry completely, refit. Two minutes. A clogged filter is the number-one cause of "it's not cooling like it used to" — the machine suffocates slowly and you blame the compressor. If the filter is torn, replace it rather than running without one; dust on the coils is a far worse problem than dust in a filter.
Monthly: coils and grilles
With the unit unplugged, vacuum the intake grilles and visible coil fins with a brush attachment. Bent fins can be gently straightened with a fin comb. Wipe the cabinet with a damp cloth — no solvents near the plastics.
As needed: the drainage system
Empty the reservoir whenever the tank-full light appears, and in humid weather give the tank a fortnightly rinse with warm water and a splash of white vinegar to stop biofilm. If you smell anything musty from the vents, run the unit on fan-only for an hour in a ventilated room after cleaning the tank and filter — mould in an air mover is a health issue, not just a smell.
Check the duct and window seal
Once a season, confirm the exhaust duct hasn't split at the seams and the window kit foam still seals. Duct tape genuinely is the right tool for a cracked duct; replacement hoses and seal kits are cheap if it's past saving.
End of season: storage
The step that decides how the unit performs next summer. Open the drain plug and empty the unit completely, then run fan-only for two hours to dry the coils and tank internally — water left inside over winter is how machines come out of storage smelling like a pond. Clean and refit the filter, coil the cord, bag the window kit and tape it to the unit (future you will be grateful), and store it upright, covered, somewhere dry. After moving it, leave it upright for two hours before running so the compressor oil settles.
When it needs more than cleaning
Weak cooling with a clean filter and sealed window suggests low refrigerant — a technician job, and on budget units often uneconomic against replacement. Loud rattles are usually a loose panel; grinding from the compressor is terminal. If it's time, our current best picks are the place to start.