When someone says their mobile air conditioner "doesn't really cool," the unit is rarely the problem — the exhaust hose setup usually is. Get these seven things right and a modest AC cools a room easily; get them wrong and even a powerful one disappoints.
1. Leaving the window unsealed
This is the number-one mistake. If the gap around the hose isn't sealed, the hot air the unit pushes outside simply flows back in, and the room never cools. Always fit a window sealing kit so the only path for that heat is out. An open, unsealed window with a hose poked through it largely defeats the AC.
2. Running too long a hose
Every extra metre of hose is more hot surface radiating heat back into your room, and more resistance for the unit to push against. Position the AC close to the window so the hose run is as short as possible. Don't stretch it across the room when a metre would do.
3. Kinking or coiling the hose
A kinked or tightly coiled hose chokes airflow, so the unit can't expel heat efficiently and works harder for less cooling. Keep the hose as straight as you can, with gentle bends only. If it sags, support it so it doesn't fold.
4. Extending the hose
It's tempting to add length to reach a distant window, but extensions add joints and resistance that leak heat and cut airflow. The unit then cools less and runs hotter. Move the AC closer to the window instead of lengthening the hose.
5. Letting the hose bake in the sun
If the hose or its window exit sits in direct sunlight, it heats up and radiates that warmth back inside. Where possible, vent on a shaded side or shade the hose, so the heat it carries actually escapes instead of soaking back into the room.
6. Not sealing other openings
Cooling a room means containing it. An open interior door or a second cracked window lets cool air escape and warm air in, so the unit endlessly fights the rest of the flat. Close the door and other windows so the AC cools one sealed space.
7. Ignoring the room's heat load
Even a perfect hose setup struggles if the room is baking from direct sun. Shade the windows during the day so the unit isn't fighting incoming heat. A shaded, sealed room lets a small unit keep up comfortably.
Get the basics right first
Before blaming the unit, check the hose: short, straight, sealed, shaded, in a closed room. Most cooling complaints vanish once these are fixed. And if you're still shopping, make sure you buy a correctly sized unit that's actually in stock near you.