FirstCheck
EN FR
🍁 Built for Canadian homes — written to Canadian codes and provincial rules. Not intended for use outside Canada.
DRAFT — this page has not yet been reviewed by a licensed professional. Editorial preview only.

Heat pump not cooling in cooling mode

A house that won't cool on a hot day is stressful — but the first things to check are usually free, and a starved-airflow fix beats a service call more often than people expect.

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

flag
Start here

In Canadian homes, pull the air filter first. A grey, clogged filter starves airflow and makes the vents feel weak and barely cool even when the system is trying to cool. A fresh filter is under $15, and clearing that restriction is the single most common fix for weak cooling.

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

Find the filter at the indoor air handler or return grille, note the size printed on its frame, and slide in a fresh one facing the airflow arrow the right way.

  1. Locate the filter slot on the indoor air handler or the large return-air grille.
  2. Slide out the old filter and read the size stamped on its cardboard frame.
  3. Insert a matching new filter with the printed airflow arrow pointing toward the unit, and set a reminder to check it monthly in cooling season.
schedule10 min savings$8–20
Pleated furnace/air-handler filterMatch the size stamped on the old filter frame (e.g. 16x25x1) and the printed airflow direction
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
Replacing a return-air filter is routine homeowner maintenance in every province.

handymanHow to fix it

warning Cut power before you rinseThe outdoor unit has a fan and live 240 V wiring. Always kill power at the disconnect or breaker and confirm the fan has stopped before clearing debris or spraying water, and keep the hose off the electrical box. Use a gentle stream, not a pressure washer — the fins bend easily. If you're not comfortable working around the disconnect, a coil clean is an inexpensive job for a technician.

Cut power to the outdoor unit, clear debris from around it, then rinse the coil fins gently from the inside out with a garden hose — never a pressure washer — and let it dry before restoring power.

  1. Turn the unit off at the thermostat, then cut power at the outdoor disconnect box beside the unit (or its breaker). Confirm the fan is fully stopped before touching anything.
  2. Clear leaves, grass, and cottonwood from around the base and pull any large debris off the fin faces by hand or with a soft brush.
  3. With a garden hose on a gentle stream — not a pressure washer — rinse the coil from the inside outward to push dirt back out the way it came. Keep water off the electrical box.
  4. Let the unit dry, restore power, and run cooling. If a coil cleaner is needed for greasy buildup, use a no-rinse coil cleaner rated for aluminum fins per its label.
schedule30 min savings$0–25
No-rinse condenser coil cleanerOptional; choose a foaming cleaner rated safe for aluminum coil fins
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
Rinsing the outdoor condenser coil is owner maintenance in every province; only refrigerant handling and sealed-system work are licensed-only.

visibilityHow to check

report Thaw it fully before running cooling againRunning the compressor with the coil iced over can slug it with liquid refrigerant and cause expensive damage, and chipping or prying at the ice will puncture the thin coil. Switch to fan-only, let it thaw on its own, and never scrape the coil. If it keeps freezing after the filter and airflow are sorted, stop and let a licensed HVAC technician check the refrigerant charge.
  1. At the indoor air handler, look at the coil and the copper refrigerant lines where they leave it — a glaze of frost or a solid coat of ice, or a pool of meltwater in the drain pan, confirms the coil has frozen.
  2. Set the thermostat to Off for cooling and the fan to On (fan-only). Running the blower with the compressor off thaws the coil fastest — expect a full thaw to take a few hours, and keep towels handy for meltwater.
  3. While it thaws, replace the air filter and make sure supply and return vents are open and unblocked, since starved airflow is the usual reason a coil freezes.
  4. Once fully thawed, run cooling again. If the coil freezes back up within a day despite clean airflow, the likely cause is low refrigerant — a licensed HVAC diagnosis.
buildNo tools schedule15 min

verifiedWhy this one goes to a pro

The reversing valve and refrigerant charge are part of the sealed system. In Canada, handling refrigerant requires certification, and valve replacement means brazing on pressurized lines. This is a licensed HVAC repair — a technician can confirm it quickly, and a leak found today saves the charge you'd otherwise lose again.

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.

verifiedWhy this one goes to a pro

The reversing valve and refrigerant charge are part of the sealed system. In Canada, handling refrigerant requires certification, and valve replacement means brazing on pressurized lines. This is a licensed HVAC repair — a technician can confirm it quickly, and a leak found today saves the charge you'd otherwise lose again.

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.