Most air conditioners that run but do not cool trace back to a dirty filter, an incorrect thermostat setting, a blocked outdoor unit, or a frozen evaporator coil. A handful of these issues can be checked safely without tools, but a hissing sound, visible ice, or a system that will not restart points to a refrigerant or mechanical problem that needs a licensed technician. Galaxy Plumbing's HVAC team diagnoses and repairs cooling failures across the GTA.
An air conditioner that runs but does not cool almost always traces back to one of four issues: restricted airflow, an incorrect thermostat setting, a dirty outdoor condenser, or low refrigerant. Airflow and thermostat problems are usually safe to check without a technician, while refrigerant and mechanical issues require a licensed HVAC professional. Working through the checks below in order rules out the simplest causes first.
A thermostat set to Heat, set above the current room temperature, or running on dead batteries stops an air conditioner from cooling even though the system otherwise runs fine. Confirm the thermostat is set to Cool with the target temperature below the room's actual temperature, and replace the batteries if the display looks dim or blank.
A programmable thermostat with a stuck or miscalibrated sensor can also misread the room. This often shows up as the system freezing overnight even though the daytime setting looks correct, which points back to the thermostat rather than the compressor.
A clogged air filter is one of the most common reasons an air conditioner runs constantly without cooling the home, since restricted airflow across the indoor coil forces the system to work harder while delivering less cold air. Check the filter and replace it if it looks gray or matted, which typically happens every one to three months during peak cooling season.
This issue shows up most often in Toronto and across the GTA during summer heat waves, when systems run for extended hours and filters clog faster than usual. A dirty filter left in place long enough can also freeze the evaporator coil, which is covered next.
Visible ice on the indoor coil or refrigerant lines, warm air from the vents, or water pooling near the air handler are signs the evaporator coil has frozen. The steps below safely thaw the coil without damaging it.
A frozen coil is a symptom rather than the underlying problem. Restricted airflow from a dirty filter or blocked vents is the most common cause, but a coil that freezes again after a proper thaw points to low refrigerant or a mechanical issue that needs a licensed technician to diagnose.
A condenser buried in leaves, grass clippings, or overgrown landscaping cannot release the heat pulled from inside the home, which reduces cooling capacity and can eventually damage the compressor. Clear at least 60 centimetres of space around the unit and gently rinse the fins with a garden hose to remove built-up dirt.
Homes in Mississauga with mature landscaping near the outdoor unit see this issue often, especially in midsummer when growth is heaviest. Never use a pressure washer on the fins, since the force can bend them and restrict airflow further. For a full seasonal inspection, the City of Toronto's heat relief guidance outlines how prolonged heat events affect residential cooling demand across the GTA.
A hissing sound near the indoor or outdoor unit, an oily residue on refrigerant lines, or cooling that gradually gets worse over several days points to a refrigerant leak. Refrigerant is not a consumable that runs low from normal use, so any low charge means the system is leaking somewhere in the line set or coils.
Refrigerant handling requires a licensed technician in Ontario. AC and heat pump work requires a 313A or 313D Certificate of Qualification from Skilled Trades Ontario, and technicians handling refrigerants must also hold an Ozone Depletion Prevention credential under Ontario's ozone-depleting substances rules. Homeowners can verify a technician's qualifications through Skilled Trades Ontario's trade registry before booking any refrigerant repair. For a broader overview of what Ontario regulations cover for refrigeration systems, the TSSA's refrigeration compliance guidance provides a useful reference for homeowners and property managers alike.
Call a licensed HVAC technician if the thermostat, filter, and outdoor unit checks do not restore cooling, if ice returns after thawing, or if the system makes a hissing, grinding, or clicking sound. Continuing to run a system with a suspected refrigerant leak or a frozen coil risks compressor damage, which is one of the more expensive repairs in a cooling system.
Galaxy Plumbing's HVAC services cover diagnostic visits, repairs, and full system replacement for homes across the GTA.
If cooling fails entirely during a heat warning, Galaxy Plumbing's emergency repairs team responds the same day.
Most no-cool calls resolve with a thermostat check, a filter change, or a cleared outdoor unit, and working through those steps first can save the cost of an unnecessary service visit. When the problem persists after basic checks or shows signs of a refrigerant leak, a same-day diagnostic visit prevents a minor issue from becoming a compressor replacement.
Homeowners weighing a system upgrade instead of another repair can compare options in Galaxy Plumbing's air conditioning installation guide for the GTA.
The Galaxy Plumbing team diagnoses no-cool AC calls across the GTA, with same-day appointments available during peak cooling season.
An air conditioner that runs but does not cool is usually caused by a dirty filter, an incorrect thermostat setting, a blocked outdoor condenser, or low refrigerant. Airflow and thermostat issues are typically safe to check yourself, while a suspected refrigerant leak needs a licensed technician. Working through each cause in order usually identifies the problem within a few minutes. For a full diagnosis, our HVAC team is available across the GTA.
Ice on an air conditioner's indoor coil or refrigerant lines forms when airflow is restricted or refrigerant is low, both of which cause the coil to run too cold. Turn the thermostat off and the fan on to thaw the coil over several hours before restarting the system. If ice returns after a proper thaw, the underlying cause needs a professional diagnosis from our HVAC specialists.
Signs of a refrigerant leak include a hissing sound near the indoor or outdoor unit, an oily residue on refrigerant lines, and cooling performance that gradually worsens over several days. Refrigerant does not run low from normal use, so any shortage means there is a leak somewhere in the system. This repair requires a licensed HVAC technician in Ontario contact our team to arrange a diagnosis.
Yes, homeowners can safely clear debris from around the outdoor condenser and rinse the fins with a garden hose on a gentle setting. Keep at least 60 centimetres of clearance around the unit for proper airflow. Avoid using a pressure washer, since the force can bend the fins and reduce cooling performance. For a thorough seasonal clean, our HVAC service includes a full condenser inspection.
Most homes need a filter change every one to three months during peak cooling season, though homes with pets or nearby construction may need more frequent changes. A clogged filter restricts airflow, which reduces cooling capacity and can cause the evaporator coil to freeze. Checking the filter monthly during summer is a reasonable habit for most GTA homes. If cooling issues persist after a fresh filter, our HVAC team can assess the system.
A single-zone installation typically takes three to five hours from mounting the indoor unit to final commissioning. Multi-zone systems with two to four indoor units usually take one full day, and larger installations can extend to two days. Any required electrical panel upgrade is scheduled separately before the ductless installation begins.
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