Window/portable AC runs but won't cool

Q: Window/portable AC runs but won't cool

In Canada, when a window or portable air conditioner runs but won't cool, the most common cause is a dirty air filter choking the airflow — free to clean. Next check the coils and the space around the unit, and make sure it isn't simply set to fan-only or eco. A unit that ices up has too little airflow or is running in cool weather; turn it to fan-only to thaw. Only after those does a sealed-system fault or low refrigerant become likely — and on a small window unit that's usually not worth repairing, so it's replaced. If you ever smell burning or hot electrical, unplug it and stop.

The fan spinning while the air stays warm is usually a small airflow problem — a clogged filter or dusty coils — not a dead unit. Most of the time the fix is free and takes fifteen minutes.

tuneWhat are you noticing?

Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.

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In Canadian homes, check the filter first. Unplug the unit, pop off the front grille, and slide out the grey mesh filter — if it's grey with felted dust, that alone can stop the cooling. Vacuum and wash it, let it dry fully, and reinstall. Free, and the single most common fix.

Ranked from real-world failure data. The order updates as you select what you’re noticing above.

Likely causes, in the order to check them

Showing the typical order

Beginner-friendly Doable, with care Safety-critical Call a pro

handymanHow to fix it

Unplug the unit, remove the mesh filter behind the front grille, vacuum and wash it in warm soapy water, dry it fully, and reinstall. Airflow and cooling return within minutes.

Turn the unit off and unplug it at the wall.
Open or lift off the front grille and slide out the filter — usually a grey plastic mesh panel that pulls straight out.
Vacuum the loose dust, then wash the filter in warm soapy water and rinse it. Let it dry completely — a damp filter can grow mould and drip.
Slide the dry filter back in, refit the grille, plug in, and run on Cool. If the filter is torn or won't come clean, a replacement is a few dollars.

schedule15 min savings$0–15

visibilityHow to check and thaw

warning Melting ice around live electricsA frozen coil means melting water right next to a plugged-in appliance. Unplug the unit before you handle the ice or the filter, and never run it on Cool while it's iced up — that can damage the compressor. Let it thaw and dry fully before power comes back on.

Unplug the unit or set it to fan-only, then look at the cold coils behind the front grille. Frost, or a solid sheet of ice, confirms a frozen coil.
Leave it running on fan-only (no cooling) for one to three hours to melt the ice completely. Keep a towel under the unit for drips and don't force the ice off — you'll bend the fins.
Once fully thawed and dry, clean or replace the filter and restart on Cool. If it ices up again with a clean filter and warm outdoor air, the airflow or the sealed system needs a closer look.

buildNo tools schedule30 min

verifiedWhy this one goes to a pro

The refrigerant loop inside the unit is sealed and under pressure. Opening it releases refrigerant — which is illegal to vent in Canada and can cause frostbite and displace breathable air in a small room. Only a certified technician may work on it, and on a small unit the honest answer is usually to replace rather than repair.

gavel Check your province first AB: licensed professionals only · BC: licensed professionals only · ON: licensed professionals only · PE: licensed professionals only · QC: licensed professionals only
Refrigerant handling and sealed-system repair require federal ODS/HFC certification and, in most provinces, a refrigeration/appliance licence — this fix is licensed-only Canada-wide. Buying and swapping in a whole new self-contained unit is owner-permitted; opening the refrigerant loop is not.

Your notes travel with the request — what you saw, what you ruled out, when it started — so the pro arrives with a head start instead of a mystery.

sort

Why the list is in this order

We don’t sort by likelihood alone. We sort the way a good, honest tradesperson thinks: rule out the free, safe, common causes first. That’s why the cheap checks outrank the expensive repairs — and why anything dangerous gets a hard stop instead of a pep talk. The order exists to save you money, not to sell you anything.