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Ductless mini-split isn't cooling

Warm rooms are frustrating in a heatwave, but the most common cause is a five-minute, no-cost fix: filters that need a wash.

tuneWhat are you noticing?
Select anything that matches and the checklist below reorders to fit. Not sure? Skip it.
emergency_home

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Start here

In Canada, start with the filters. Lift the front cover of the indoor head, slide out the mesh filters, and hold them to the light — if they're grey with dust, that's almost certainly why cooling is weak. Rinsing them clean and letting them dry is 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

Lift the front cover of the indoor head, slide out the mesh filters, rinse them under lukewarm water (a little mild soap for greasy dust), let them dry fully, and slide them back in.

  1. Turn the head off and lift the hinged front cover until it clicks — the mesh filters sit just inside.
  2. Slide each filter out by its tab and rinse it under lukewarm running water; for greasy kitchen dust, a little mild dish soap helps. Don't use hot water, which can warp the mesh.
  3. Shake off the water and let the filters air-dry completely — installing them damp invites mould.
  4. Slide the dry filters back in, close the cover, and set a reminder to clean them every two to four weeks during cooling season.
schedule10 min savingsusually free
gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Cleaning the indoor filters is routine homeowner maintenance in every province.

visibilityHow to check

  1. Go to the outdoor unit and look at the coil fins on its sides — they should be clean and open, not matted with leaves, grass clippings, dust, or cottonwood fluff.
  2. Check that nothing crowds the unit: give it clear space on all sides and above so its fan can pull air through freely.
  3. If the fins are dirty, that's your lead — clean it with the power off (see the fix). If they're clean and clear but cooling is still weak, move on to checking for ice or low refrigerant.
buildNo tools schedule10 min

handymanHow to fix it

report Kill the power before you touch the outdoor unitThe outdoor fan can start on its own when the system calls for cooling, and it moves with real force. Before brushing or rinsing anything, switch the unit off and cut power at its disconnect or breaker, and keep the hose away from the electrical box. If you're not sure where the disconnect is, this is a quick, cheap job for a technician.

With the power off at the disconnect or breaker, brush loose debris off the outdoor coil fins and give them a gentle rinse from a garden hose (never a pressure washer), keeping water off the electrical box.

  1. Switch the unit off and turn off power at its outdoor disconnect or the breaker — the fan must not be able to start while you work.
  2. Pull leaves and loose debris away by hand or with a soft brush, working along the direction of the fins so you don't bend them.
  3. Rinse the fins gently with a garden hose from the inside out if you can reach, keeping the stream low-pressure and away from the electrical box. Never use a pressure washer — it flattens the fins.
  4. Let it dry, clear at least a couple of feet of space around the unit, then restore power and run it in Cool to confirm the airflow is back.
schedule20 min savingsusually free
gavel Check your province first AB: homeowner may do this · BC: homeowner may do this · ON: homeowner may do this · PE: homeowner may do this · QC: homeowner may do this
Cleaning the outdoor coil with the power off is permitted homeowner maintenance; opening the sealed refrigerant system is licensed-only.

visibilityHow to check

warning Let it thaw — never chip the iceThe indoor coil is thin aluminum wrapped around pressurized refrigerant tubing. Scraping, prying, or hammering ice off it can puncture the coil and turn a filter problem into an expensive sealed-system repair. Let the ice melt on its own; if it keeps re-freezing after clean filters and a full thaw, have a licensed HVAC technician look at it.
  1. Turn the head off, then lift the front cover and slide out the filters so you can see the finned coil behind them.
  2. Look for frost or a solid coat of ice on the coil — light beading is fine, but a white glaze of ice is not, and it means airflow has been choked.
  3. If you find ice, leave the unit off (or run it in Fan-only) and let it thaw completely — never scrape or chip the ice off the coil. Wash the filters before you run it in Cool again.
buildNo tools schedule10 min

verifiedWhy this one goes to a pro

The refrigerant charge and the compressor are part of the sealed system. In Canada, handling refrigerant requires certification, and there is no legal DIY "top-up" — a low charge means a leak that must be found and repaired. This is licensed HVAC work; a technician can confirm it quickly.

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.