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🍁 Built for Canadian homes — written to Canadian codes and provincial rules. Not intended for use outside Canada.

AC running but blowing warm air

Annoying — but usually not a disaster. Most of the time this is a $20 part or a free fix.

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

Check the run capacitor first. It's the single most common reason a running AC blows warm air — and checking is free. Turn off power at the breaker, open the small side panel, and look at the round canister: a healthy one has a flat top.

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

visibilityHow to check

  1. Turn the AC off at the breaker panel AND pull the gray disconnect near the outdoor unit.
  2. Unscrew the small side access panel on the outdoor unit.
  3. Look at the round canister's top. Flat is fine. Puffed up or leaking means it's failed.
buildscrewdriver schedule15 min

handymanHow to fix it

report One rule before you touch itCapacitors hold a strong electric charge even after the power is off — and a dual run capacitor holds it on more than one pair of terminals. Short across each pair (Common-to-HERM, then Common-to-FAN) with an insulated discharge tool before touching any terminal. If that step doesn't sit right with you, stop: for a pro this is a quick, inexpensive visit.

Photograph the wiring, discharge the old capacitor, swap in a replacement with the same µF and voltage rating, reconnect wire-for-wire.

schedule30 min savings$14–28
Dual run capacitorMatch the µF and voltage printed on your old canister $14–28 open_in_new Insulated capacitor discharge tool
We may earn a commission on this link.
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
Component replacement on the line-voltage side of owner-occupied equipment; no refrigerant handling involved.

visibilityHow to check

  1. Walk out to the outdoor unit and look at the metal fins around its sides.
  2. A gray blanket of dust, grass clippings, or cottonwood fluff on the fins means the unit can't shed heat — that's the whole diagnosis.
  3. While you're there, clear anything crowding the unit: it wants about 60 cm of open air on all sides.
buildNo tools schedule2 min

handymanHow to fix it

warning Power off before waterKill the power at the disconnect or breaker before rinsing. Water and a running condenser don't mix, and the fan can start on its own when the thermostat calls.

Turn off power at the outdoor disconnect, then rinse the fins gently with a garden hose from the inside out if you can, or top-down from outside. No pressure washer — it folds the fins flat. Let it dry, restore power.

  1. Turn the AC off at the thermostat, then pull the gray disconnect near the outdoor unit (or flip its breaker).
  2. Rinse the fins with a garden hose at normal pressure, working top to bottom. Never use a pressure washer — it flattens the fins and makes things worse.
  3. If the mat of debris is thick, a soft brush stroke in the direction of the fins (never across) loosens it first.
  4. Let the unit dry for a half hour, restore power, and give it 15 minutes of runtime before judging the result.
schedule20 min savingsusually free

visibilityHow to check

  1. Pull the air filter and hold it up to a light. If you can't see light through it, it's choking the system.
  2. Check the copper lines at the indoor unit and outdoor unit for frost or ice. Ice plus weak airflow is the classic frozen-coil pattern.
  3. Weak, cool-ish air from the vents (not warm, not cold) is the other tell — the coil is iced over and air can't pass through it.
buildNo tools schedule5 min

handymanHow to fix it

Switch the system to FAN ONLY (cooling off) and let the ice melt fully — typically 2 to 4 hours. Fit a fresh filter, then run cooling again. If it re-freezes with a clean filter and open vents, stop there: persistent freezing points to refrigerant or airflow issues a technician should chase.

  1. At the thermostat, turn cooling OFF and the fan to ON. The moving air thaws the coil from the inside; expect 2–4 hours.
  2. While it thaws, fit a new filter — match the size printed on the old one's frame. Note the airflow arrow on the frame; it points toward the furnace/air handler.
  3. Open any closed supply vents; a starved system freezes again even with a clean filter.
  4. Run cooling and check the lines an hour later. Re-freezing with a clean filter and open vents means it's time for a technician.
schedule15 min savings$8–15
Furnace/air-handler filterMatch the size printed on your old filter's frame (e.g. 16×25×1)

verifiedWhy this one goes to a pro

Finding a leak, repairing it, and recharging the system means opening the sealed refrigerant circuit. In Canada that work is restricted to certified technicians under federal halocarbon rules — it isn't a homeowner task in any province, and venting refrigerant is an offence. The good news: your observation ("ice on the lines, weak cooling for weeks") is exactly the head start a tech wants.

report Sealed-system work is licensed-onlyThe reversing valve and refrigerant charge are part of the sealed system. In Canada, working with refrigerant requires certification, and valve replacement means brazing on pressurized lines. This is a licensed HVAC repair — a technician can confirm it quickly.
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 requires certification across Canada under the federal Ozone-depleting Substances and Halocarbon Alternatives Regulations; provinces layer their own trade licensing on top.

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

Swapping the motor means working inside the unit at the capacitor and line-voltage wiring, and matching the motor's specs exactly. Meanwhile, running the system with a dead fan can overheat the compressor — the most expensive part in the machine. Keep the system off until it's fixed.

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.