Window AC Not Cooling: What to Check, in Order

By Ray Bennett · Updated 2 October 2026 · 6 min read · Checked against the sources at the end

Window AC Not Cooling: What to Check, in Order

Short answer

A window unit is one box with a cold half facing the room and a hot half facing outside. A lot of complaints are the hot half being unable to get rid of its heat, and the coil out there is the one nobody ever cleans. Before any of that, check the mode, because Energy Saver makes a working unit go silent for minutes at a time and it gets reported as a fault constantly.

A window air conditioner is the whole system squeezed into one box. The cold half faces your room, the hot half hangs outside, and a divider down the middle keeps them apart.

Much of what goes wrong is the hot half struggling to get rid of its heat, or the two halves mixing. Once you see it that way the checks sort themselves into an order.

Before you start

What to carry: a screwdriver, a soft brush, a vacuum and washing up liquid. Half an hour, and most of it is cleaning.

Gas or electric? Electric, and it plugs into a wall socket like a kettle, which is the one genuinely good thing about a fault on one of these. You can unplug it completely before touching anything.

Look at the back of it. Go outside, or lean out, and look at the half that hangs out of the window. Most people have never seen it, and it is where this page spends most of its time.

Two things before you open it up. Unplug it, do not just switch it off. There is a capacitor inside a window unit exactly as there is in a big system, and it holds a charge after the plug is out. Unplug it, leave it, and keep your fingers out of the electrical side.

Never run one on an extension lead. A window unit pulls a heavy surge every time the compressor starts, and a thin lead handling that can melt a plug or start a fire. Straight into a wall socket, on its own.

One box, two halves

Three things to clean. GE calls the filter the most important, and the one outside gets touched least.

Check 1

The filter, then both coils

The filter. Behind the front grille, and it slides or clips out. It is meant to be washed, roughly monthly through the season. Warm soapy water, rinse, dry it completely, put it back. Never run the unit without one, because the dust then goes straight into the coil where you cannot get at it.

The front coil. The fins just behind the filter. A soft brush and a vacuum, working along the fins rather than across them so you do not fold them over.

The coil at the back. This is the one. It sits outside collecting leaves, seed, grit and cobwebs, and it is where all the heat from your room is supposed to leave. Matted over, the unit runs and runs and never gets the room down, and it gets worse every hot day because that is when it matters most.

On most units the case lifts off with a few screws once it is unplugged, and cleaning that rear coil properly can make a real difference to an older machine. Rinse gently, never with a hose or a pressure washer, which GE says makes water more likely to get into the electronics.

The settings that look like a fault

All three of these get reported as broken units. None of them is.

Check 2Free, a minute

Put it on plain Cool while you test

Energy Saver, or ECO. On that setting the fan stops when the compressor stops, so the unit goes completely silent for minutes at a time and feels like it has died. It has not. Switch to normal Cool while you are working out what is going on, and put it back afterwards if you like it.

Fan only. Air moves, the room sounds like it is being cooled, and nothing is being cooled at all. It is easier to hit by accident than it sounds.

The restart delay. About three minutes, GE says, before the compressor starts again after the unit has been off. Standing there pressing the button starts that wait over.

Sleep mode. Many units quietly raise the temperature over the night on purpose, so a room that is comfortable at midnight and warm at five is the unit following its programme.

Air going round instead of through

Check 3

Seal it, clear it, and tilt it

The side panels and the gaps. Those concertina panels either side, and the gap where the two sashes meet above the unit, are where hot air from outside comes straight back in. Foam strip in that sash gap is cheap and makes a real difference.

Clearance at the back. A bush, a fence, a balcony wall or a fly screen pressed against it means the unit breathes its own hot exhaust. It needs open air behind and above.

The tilt. A window unit should sit very slightly nose up, so it drains to the outside. Tilted into the room puts condensate on your floor and fills the base pan.

What is in front of it. Curtains, a sofa back, or a bed pushed against it all stop the cold air reaching the room and send it straight back into the return.

Afternoon sun on the outside half. A unit on a west wall is working against direct sun on its hot coil for the worst hours of the day, and shade helps it more than people expect.

When it is a real fault, and when to stop spending

If it is clean, sealed, on Cool, and still not cooling, there are three pictures worth telling apart.

The fan runs and the back never gets warm. The compressor is not starting. Capacitor, overload or the control board, and on a window unit those are behind panels with mains and a charged capacitor in reach.

The fan runs, the back gets properly hot, and the air is only slightly cool. Usually low refrigerant. Window units are sealed and were never designed to be topped up at a sensible price.

Ice on the front coil. Switch it to fan only until it has thawed, then work backwards: airflow first, refrigerant second. If it also trips the breaker or its own plug button, that is a separate trail: what tripping is telling you.

Before paying for a big repair, check the price of a new window unit, so you know which makes more sense before anybody opens it.

One more thing to rule out before blaming the machine: a unit sized for a bedroom will never cool an open plan room, no matter how well it is running. Check its rating against the room before assuming a fault (ENERGY STAR’s BTU chart), and remember that too large is its own problem, leaving a room damp and clammy: why bigger is not better.

Questions people ask

It makes a ticking or spattering sound when it runs.

That is normal and it is meant to happen. The fan at the back has a ring that picks condensate out of the base pan and flicks it onto the hot coil, which helps it cool and gets rid of the water at the same time.

Water is dripping inside the room.

The tilt, Midea says. It should sit very slightly nose up so the water runs out of the back, and a unit that has sagged over a season does this.

Can a window unit be recharged with refrigerant?

Technically yes and practically no. They are sealed, the labour costs more than the machine, and a unit that has lost its charge has a leak that will not have fixed itself.

How often should the filter be washed?

Monthly through the season, and more often with pets or an open window nearby. It is two minutes and it is the difference between a unit that copes in August and one that does not.

One side of the room is cold and the other is not.

That is a single box blowing in one direction rather than a fault. Aim the louvres across the room rather than at the nearest wall, and a small fan moving the air around does more than turning the temperature down.

It got much louder this summer.

Look at what is loose before you worry. The case screws and the mounting brackets rattle as things settle: which noises matter and which do not.

Sources: GE room air conditioner owner's manuals 39-7388-1 and 49-7754 (filter every 30 days, three minute restart, extension cords, tilt), GE Appliances "Air Conditioner - Odor" and "Air Conditioner - Slinger Ring", Frigidaire support "Room Air Conditioners - What is Econ mode?", Midea window air conditioner FAQ (tilt, Energy Saver), and ENERGY STAR "Room Air Conditioners" sizing and savings tips