Why Is My Air Conditioner Running but Not Cooling?
It’s a hot day in Sault Ste. Marie. Your air conditioner is running — you can hear it humming — but your home still feels warm and stuffy. What gives?
This is one of the most common problems we hear from homeowners in Northern Ontario during the summer. In this blog post, we’ll break down the 7 most likely reasons your AC is running but not cooling, how to troubleshoot it, and when it’s time to call the experts at Stellar Comfort.
1. Your Air Filter Is Clogged
A dirty air filter restricts airflow, causing your system to run longer and work harder — but without effectively cooling your space.
What to do:
Check your filter. If it’s gray, dusty, or hasn’t been changed in the last 1–3 months, replace it. This alone can restore performance quickly.
2. Your Thermostat Is Set Incorrectly
It sounds basic, but it happens all the time: the thermostat is set to "fan" instead of "cool," or it’s reading the wrong temperature because it’s near a window or heat source.
What to do:
Double-check that your thermostat is:
Set to “Cool”
Set at least 2–3°C lower than the current room temperature
Away from direct sunlight or heat sources
3. Your Outdoor Unit Is Dirty or Blocked
Your AC’s outdoor condenser needs airflow to release heat from your home. If it’s clogged with leaves, dust, or weeds, it can’t do its job — so your home stays warm.
What to do:
Clear away debris from around the unit. Use a hose to gently rinse the fins (turn off power first), or call us for a full condenser cleaning.
4. Low Refrigerant Levels
If your system is blowing warm or only mildly cool air, low refrigerant may be to blame. This can be caused by leaks or system wear.
What to do:
This isn’t a DIY fix. You’ll need a licensed HVAC technician (like Stellar Comfort) to inspect the system, find any leaks, and recharge it safely.
5. Your Evaporator Coil Is Frozen
Yes, frozen. Poor airflow or low refrigerant can cause the indoor coil to freeze over — which means your system can’t absorb heat from your home.
Signs of a frozen coil:
Ice around your indoor unit
Reduced airflow
AC runs continuously with little effect
What to do:
Turn off your system and call for service. Continuing to run a frozen AC can damage the compressor.
6. Your AC Is Too Small for Your Home
In older homes across Sault Ste. Marie and Algoma, it’s common to have undersized AC units that struggle in extreme heat.
What to do:
If your system has always struggled to cool your space, it may be time to look into zoned cooling, a ductless mini-split, or a properly sized central air upgrade.
7. Your System Is Simply Too Old
If your AC is over 12–15 years old, lack of cooling may be a sign that it’s near the end of its lifespan. Older systems lose efficiency, break down more often, and cost more to run.
What to do:
Schedule an inspection. Stellar Comfort offers free consultations and owned AC systems starting from $75/month — no rental contracts, no surprise fees.
Still Not Cooling? Let Stellar Comfort Fix It.
Whether it’s a quick filter swap or a full system replacement, we’re here to keep your home cool and comfortable. At Stellar Comfort, we proudly serve Sault Ste. Marie and the Algoma Region with honest advice, expert service, and real ownership options.