AC Not Cooling? What to Check Before You Call
An air conditioner that runs but doesn’t cool is one of the most common summer calls we get in Mississauga. Sometimes it’s a part that’s failed. Often it’s something you can check yourself in ten minutes.
1. Thermostat
Set to Cool, fan on Auto, setpoint a few degrees below room temperature. If it’s a battery thermostat with a blank or flickering screen, change the batteries.
2. Is the outdoor unit running?
Go outside. You should hear the compressor and see the top fan spinning. If the indoor fan is blowing but the outdoor unit is silent, check the AC breaker in the panel and the disconnect box beside the unit. A unit that hums but the fan doesn’t spin often has a failed capacitor. Don’t poke at it; capacitors hold a charge.
3. Filter and airflow
A plugged filter reduces airflow so much that the indoor coil can freeze. Replace it, and make sure supply registers and return grilles aren’t blocked.
4. Look for ice
Ice on the copper lines at the outdoor unit or on the indoor coil means airflow is too low or refrigerant is low. Turn the AC off and run the fan only for a few hours to thaw it. If it freezes again after a new filter, you need a technician. Our post on why air conditioners freeze up explains it in more detail.
5. Dirty outdoor coil
Cottonwood fluff and grass clippings mat on the coil fins. With the power off, rinse it gently with a garden hose from the inside out.
6. Water around the furnace
A clogged condensate drain can trip a float switch that shuts the AC off. If there’s water in the drain pan or on the floor, that’s likely the cause.
When it’s time to call
If the outdoor unit won’t start, the breaker keeps tripping, the coil keeps freezing, or the system runs all day and can’t get below 25°C on a mild day, it needs a technician. Our AC not cooling guide has a few more checks. For repairs in Mississauga and the GTA, see our air conditioning services or call 647-657-2977.
