Air Conditioner Not Cooling the House

When your air conditioner runs but doesn't cool the house, it's uncomfortable and inefficient. This is a common complaint during Canadian summers, particularly in Southern Ontario and the Prairies where temperatures can exceed 35°C. Several of the most common causes can be addressed by homeowners before scheduling a service call (typically CAD $150–$300).

A dirty air filter restricting airflow is the most frequent cause. Dirty or obstructed condenser coils on the outdoor unit reduce heat dissipation. Low refrigerant levels from a slow leak, a frozen evaporator coil, or a faulty capacitor are more technical causes. Thermostat misconfiguration or a tripped breaker can also masquerade as a cooling failure.

A replacement air filter (CAD $8–$18), a garden hose for cleaning the outdoor unit, and a screwdriver to remove the condenser fan guard. A fin comb (CAD $10–$15) is useful for straightening bent condenser fins.

1. Check and replace the air filter if dirty — this is the number-one fix.
2. Verify the thermostat is set to COOL and the fan is set to AUTO, not ON.
3. Check the circuit breaker — AC systems often have a separate breaker.
4. Inspect the outdoor condenser unit — clear away any debris, leaves, or vegetation within 60 cm of the unit.
5. Gently hose down the condenser coils from the inside out to remove dirt and debris. Turn off the unit first.
6. Check for ice on the refrigerant lines or indoor coil — if frozen, turn the system to FAN ONLY for 2–3 hours to thaw, then restart.
7. Ensure all supply and return vents inside the house are open and unobstructed.

If the system freezes up repeatedly, the cooling capacity has noticeably decreased over time, or the outdoor unit makes unusual sounds, call a licensed HVAC technician. Refrigerant leaks require professional repair and recharging — handling refrigerant without certification is illegal in Canada under federal environmental regulations.