An air conditioner that won't cool almost always comes down to a handful of causes. A couple you can check yourself in two minutes; the rest involve refrigerant and electrical work that should be left to a licensed technician. Here's how to figure out which you're dealing with — fast, on a hot day.
Start with the thermostat and the filter
Confirm the thermostat is set to Cool, the target is below room temperature, and the fan is on Auto (On runs the blower constantly, which feels like warm air between cooling cycles). Dying thermostat batteries cause intermittent operation — swap them.
Then check the air filter. A clogged filter is the single most common cause of weak cooling and a frozen coil — it chokes airflow, the indoor coil ices over, and almost no cold air reaches your rooms. If you can't remember the last time you changed it, that's likely your answer.
Is the outdoor unit running — and is there ice?
- Tripped breaker: AC units draw a lot of power. Check the panel for a tripped breaker for the condenser or air handler before anything else.
- Frozen coil: if you see ice on the copper lines or the indoor coil, turn the AC OFF and the fan ON to thaw it (often a dirty filter or low refrigerant). Running it frozen can damage the compressor.
- Blocked condenser: the outdoor unit needs clear airflow. Clear leaves, grass clippings, and anything within about two feet of it.
- Outdoor unit silent: if the fan and compressor outside aren't running at all (and the breaker's fine), it's usually a failed capacitor or contactor — a tech repair.
What needs a licensed technician
Low refrigerant is not a top-up — it means there's a leak, which has to be found and sealed, then the system properly recharged with the correct refrigerant. A failing compressor, capacitor, or fan motor, and any electrical fault, also need a pro. If your system still runs on R-22 refrigerant or is over 12–15 years old, a major repair is often the moment to weigh repair against replacement.
If you've checked the thermostat, filter, breaker, and outdoor unit and you're still blowing warm on a hot day, call us — we run 24/7 emergency dispatch across the GTA and carry common parts on the truck.
Want a straight answer for your home?
We give you a written price before any work starts — the estimate is free and there's no obligation.
Questions, answered
Why is my AC running but not cooling?
The most common causes are a dirty filter (which freezes the coil and chokes airflow), a thermostat set to Fan On instead of Auto, a tripped breaker, a blocked outdoor unit, or low refrigerant from a leak. Check the filter, thermostat, and breaker first; refrigerant and electrical faults need a technician.
Why is my AC frozen / icing up?
Ice on the coil or lines usually means restricted airflow (a dirty filter or blocked vents) or low refrigerant. Turn the AC off and the fan on to thaw it, replace the filter, and if it ices up again, call a technician — running it frozen can damage the compressor.
Can I fix my AC myself?
You can safely check the thermostat, replace the filter, reset a tripped breaker, and clear debris from the outdoor unit. Anything involving refrigerant, the compressor, capacitor, or wiring should be left to a licensed technician.
Should I repair or replace an AC that won't cool?
If your AC still uses R-22 refrigerant or is over 12–15 years old and the repair is a big share of a new unit's cost, replacement usually makes more sense — and a heat pump cools like an AC plus qualifies for a rebate. We'll show you both options in writing.
