Why Is My AC Not Cooling? Causes, Checks and Fixes
An air conditioner that runs but does not cool is usually failing at one of three things: it cannot move enough air, it cannot reject heat outside, or it has lost refrigerant. Some of those you can check yourself in ten minutes with no tools. Others are electrical or refrigeration faults that a licensed technician has to handle, and in Ontario one of them is illegal for a homeowner to touch at all. This guide separates the two honestly, starting with everything free.
The short answer: the most common reason an AC runs without cooling is restricted airflow from a clogged filter or a frozen evaporator coil, followed by a dirty outdoor condenser, a tripped breaker, a failed run capacitor, and low refrigerant from a leak. Check the filter, thermostat, breaker and outdoor unit first, because those four are free and account for a large share of no-cool calls.
If the free checks come back clean, the fault is almost certainly electrical or refrigeration-side. Aire One Peel offers air conditioner repair across Peel Region with 24/7 emergency availability.
Key takeaways
- Air blowing but not cold usually means airflow or refrigerant. No air at all usually means power or the blower.
- A frozen evaporator coil is a symptom, not a cause. Thawing it without fixing the airflow just refreezes it.
- Refrigerant is not consumed. If a system is low, it has a leak, and topping it up without repair is money burned.
- In Ontario you cannot legally buy or handle refrigerant without an Ozone Depletion Prevention certificate.
- An AC is designed to cool roughly 11 degrees Celsius below the outdoor temperature, so on a 35 degree day a 24 degree house is normal, not a fault.
What this guide covers
- First, is it actually broken?
- Match your symptom to the likely cause
- Six checks you can do in ten minutes
- Frozen coil: what to do and what not to do
- What needs a licensed technician, and why
- The refrigerant question, answered honestly
- AC not cooling finder
- When it is worth repairing and when it is not
- How we know this
- Frequently asked questions
First, Is It Actually Broken?
A residential air conditioner is designed to pull indoor temperature roughly 11 degrees Celsius below the outdoor temperature, not to hit any number you choose on a heatwave. On a 35 degree Peel afternoon, a house sitting at 24 degrees is performing exactly as designed, even though it feels like the system is losing. Before troubleshooting, check the actual gap rather than the setpoint.
Two other normal-but-frustrating situations get mistaken for faults. If the thermostat fan is set to ON instead of AUTO, the blower runs continuously and pushes room-temperature air between cooling cycles, which feels like the AC has stopped working. And a home that was allowed to heat up all day takes a long recovery run to pull back down, which in Ontario often lands inside the expensive afternoon electricity block. Our guide to AC energy saving tips for Ontario homes covers that timing problem in detail.
Match Your Symptom to the Likely Cause
What the system is doing narrows the cause faster than any other single piece of information, because airflow faults, power faults and refrigerant faults present differently. Find your row before working through the checks.
| What you are seeing | Most likely cause | Next step |
|---|---|---|
| Plenty of air, not cold, outdoor fan spinning | Dirty filter or coil, or low refrigerant | Filter and outdoor coil first, then a diagnostic |
| Weak airflow from every vent | Frozen evaporator coil or clogged filter | Look for ice, then thaw and replace the filter |
| No air from any vent | Blower motor, air handler power, or a tripped float switch | Check the indoor switch and breaker, then call |
| Outdoor unit hums, fan not turning | Failed run capacitor or seized fan motor | Turn the system off and call. Do not open the panel. |
| Outdoor unit completely silent | Tripped breaker, pulled disconnect, or failed contactor | Check breaker and disconnect, reset once only |
| Ice on the copper line or indoor coil | Restricted airflow or low refrigerant charge | Thaw fully, fix airflow, call if it returns |
| Cools, but never on the hottest days | Dirty coils, low airflow, or undersized system | Book maintenance before assuming failure |
| Breaker trips repeatedly | Electrical fault or failing compressor | Stop resetting it and call |
| Water pooling near the indoor unit | Blocked condensate drain | Call. The float switch may have shut cooling off. |
| Heat pump blowing warm on a cooling call | Reversing valve or control fault | Technician diagnostic |
Six Checks You Can Do in Ten Minutes
Work through these in order, because each one rules out a cause and several of them are the entire fix. All six are free, need no tools, and involve nothing more dangerous than a light switch and a garden hose.
| # | Check | What you are looking for | If it is wrong |
|---|---|---|---|
| 1 | Thermostat mode and fan setting | Set to COOL, fan on AUTO, setpoint below room temperature | Fan on ON blows uncooled air between cycles. Switch to AUTO. |
| 2 | Thermostat batteries and display | A blank or dim screen, or a low-battery icon | Replace batteries. A dying thermostat stops calling for cooling. |
| 3 | Air filter | Light should pass through it when held up | Replace it. A clogged filter is the single most common cause of a no-cool call. |
| 4 | Breaker panel and outdoor disconnect | A tripped breaker, or a pulled disconnect beside the outdoor unit | Reset once. If it trips again, stop and call. Repeated tripping is an electrical fault. |
| 5 | Outdoor condenser | Fan spinning, coil clear of grass, leaves, cottonwood fluff and shrubs | Power off at the disconnect, rinse the coil gently from outside in, clear 60 cm around the unit. |
| 6 | Supply and return vents | Open, unblocked by furniture, rugs or boxes | Open them. Closing vents to "save energy" raises static pressure and reduces total cooling. |
If all six pass and the house still will not cool, the remaining causes are inside the sealed refrigeration circuit or the electrical components, and that is the point where a homeowner stops and a technician starts.
Frozen Coil: What to Do and What Not to Do
Ice on the indoor coil or on the copper line running to the outdoor unit means the coil dropped below freezing, which happens when airflow across it is restricted or when refrigerant charge is low. The ice is the symptom. Melting it without fixing the underlying cause simply buys a few hours before it refreezes.
| Step | Do this | Do not do this |
|---|---|---|
| 1. Stop cooling | Set the thermostat to OFF so the compressor stops making more ice | Do not keep running it and hope it clears |
| 2. Move air | Set the fan to ON so warm indoor air melts the ice faster | Do not chip, scrape or pry at the ice; the coil fins and tubing damage easily |
| 3. Manage water | Put towels under the indoor unit and check the condensate pan | Do not use a hair dryer, heat gun or open flame on the coil |
| 4. Fix the cause | Replace the filter, open all vents, clear the return | Do not restart cooling until every visible trace of ice is gone |
| 5. Watch it | Run cooling and check the coil after a few hours | Do not ignore a second freeze; that points to charge or a blower fault |
A coil that freezes once after a neglected filter is a maintenance story. A coil that freezes again within days, with a clean filter and open vents, is a refrigerant or airflow fault that needs measurement, not guesswork.
What Needs a Licensed Technician, and Why
Everything past the six free checks involves either live high-voltage components or the sealed refrigerant circuit, and both carry real consequences for getting it wrong. The table below is not a sales pitch; it is the honest division between what you can safely resolve and what you cannot.
| Cause | Typical symptom | Who handles it |
|---|---|---|
| Clogged filter or blocked vents | Weak airflow, coil icing | Homeowner |
| Dirty outdoor coil | System runs constantly, cools poorly on hot days | Homeowner (rinse) or technician (deep clean) |
| Tripped breaker or pulled disconnect | Outdoor unit silent, indoor fan may still run | Homeowner once; technician if it repeats |
| Failed run capacitor | Outdoor unit hums but the fan does not spin | Technician. Capacitors hold a lethal charge after power is off. |
| Failed contactor | Outdoor unit will not start on a call for cooling | Technician |
| Blower motor failure | No air at any vent, indoor unit silent or humming | Technician |
| Condensate float switch tripped | Cooling stops but power is fine, water near the indoor unit | Technician (the drain is blocked) |
| Low refrigerant from a leak | Warm air, icing, longer run times, hissing | Technician only. ODP certificate legally required. |
| Compressor failure | Outdoor unit trips the breaker or runs without cooling | Technician. Usually a repair-or-replace decision. |
| Heat pump stuck in heating | Blows warm air on a cooling call | Technician (reversing valve or control fault) |
One safety line worth reading twice. Do not open the electrical compartment of the outdoor unit, even with the breaker off. Run capacitors store a high-voltage charge after disconnection and have injured and killed people who assumed cutting power made them safe. Discharging one correctly requires the right tool and the right technique.
Also stop immediately if a breaker trips a second time. A repeatedly tripping circuit is reporting a fault, and resetting it again is the one homeowner action on this page that can start a fire.
The Refrigerant Question, Answered Honestly
Refrigerant is not a consumable, so a system that is low on it has a leak somewhere in the sealed circuit. This matters because a great deal of online advice, most of it written for the United States, treats an annual top-up as routine maintenance. It is not. Adding refrigerant without finding the leak means paying for gas that will escape again, and every escape is both a repeat repair bill and a greenhouse gas release.
In Ontario, handling refrigerant is regulated, not merely discouraged. Under Ontario Regulation 463/10, Ozone Depleting Substances and Other Halocarbons, made under the Environmental Protection Act, a person must hold an Ozone Depletion Prevention certificate issued through the Ministry of the Environment, Conservation and Parks to purchase and handle refrigerants and service refrigeration equipment. That regulation replaced the older O. Reg. 189/94 on January 1, 2011. The DIY recharge cans sold widely to American homeowners have no lawful equivalent here for a homeowner working on their own central system.
There is a second reason to care in 2026. New residential air conditioners and heat pumps now ship with lower global warming potential refrigerants, principally R-454B and R-32, replacing R-410A in new equipment under Canada's hydrofluorocarbon phase-down. Existing R-410A systems remain legal to service and recharge, and nothing requires you to replace a working unit. What has changed is price: R-410A service refrigerant has become steadily more expensive as supply tightens, which shifts the arithmetic on a large leak repair in an older system. [VERIFY: confirm the exact Canadian cutoff dates against Environment and Climate Change Canada before adding any specific date here.]
AC Not Cooling Finder
Answer three questions and this points at the most likely cause and tells you plainly whether it is yours to fix or ours. Every answer it gives already appears in the tables above, and it never recommends a service call for something you can solve with a filter.
What is your AC actually doing?
When It Is Worth Repairing and When It Is Not
Most no-cool faults are worth repairing, because capacitors, contactors, float switches and blower motors are all modest parts on an otherwise sound system. The decision only gets difficult when the failure is a compressor or a significant refrigerant leak in an older unit.
| Situation | Usual call | Why |
|---|---|---|
| Capacitor, contactor or float switch on a unit under 12 years | Repair | Small part, sound system, quick fix |
| Blower motor on a unit under 12 years | Repair | Larger part but still well short of replacement cost |
| Small accessible leak on a unit under 10 years | Repair the leak, then recharge | Leak repair first is the only version that lasts |
| Large or coil leak on an R-410A unit over 12 years | Get both quotes | Rising R-410A service prices change the arithmetic |
| Compressor failure out of warranty | Usually replace | Compressor plus labour approaches a new system |
| Recurring faults, unit over 15 years | Replace | Repairs stack up and efficiency has already been lost |
For what individual repairs actually cost in this market, see our guide to AC repair cost in Mississauga. If replacement is on the table, current offers and rebates are worth checking first, and financing and rent-to-own are available.
Possible downside, stated plainly. A diagnostic visit costs money even when the answer turns out to be a filter, which is exactly why the six free checks come first on this page rather than after a booking form. And if your system is past 15 years with a failed compressor, we will tell you that another repair is throwing good money after bad, even though the repair is the easier sale.
How We Know This
The regulatory and safety statements on this page are sourced directly: Ontario Regulation 463/10 for refrigerant handling and certification, and the Ontario Ministry of the Environment, Conservation and Parks for the Ozone Depletion Prevention certificate requirement. No claim here is second-hand from another contractor's blog.
The failure-frequency ordering comes from Aire One Peel's own summer service work across Mississauga, Brampton, Caledon, Bolton, Milton, Georgetown and Etobicoke. [INSERT AIRE ONE PEEL DATA: number of no-cool service calls completed in the Peel Region between May and August 2025, and the breakdown of primary findings by category (airflow, electrical, refrigerant, controls). State the N. Do not publish a percentage on a base of fewer than 30 jobs.]
Compiled by Mario Vaghei, General Manager, in July 2026.
What to Do Next
Do the six checks first if the system is still running and blowing air. They cost nothing, take ten minutes, and resolve a large share of no-cool calls outright.
Turn the system off and call if a breaker has tripped twice, the outdoor unit is humming without the fan turning, you smell burning, or you can see ice that keeps returning. Continuing to run a system in those states makes the repair bigger.
Book a diagnostic if the six checks pass and the house still will not cool. That is the point where the remaining causes all require measurement. Aire One Peel offers air conditioner service in Mississauga and across Peel Region.
Book maintenance instead if the system cools but struggles on the hottest days. That is usually a capacity problem from dirty coils or low airflow, not a failure. AC maintenance and protection plans cover it.
Company overview from Aire One Peel Heating and Cooling, introducing the residential heating and cooling services offered across Mississauga and the Peel Region.
Checks done and still not cooling?
If the filter, thermostat, breaker and outdoor unit all check out, the fault is electrical or refrigeration-side and needs measurement. We diagnose, explain what we found, and tell you honestly whether it is worth fixing. 24/7 emergency service, free in-home estimates on replacement.
Aire One Peel Heating & Cooling
1625 Courtneypark Dr E, Mississauga, ON L5T 1V9
905-564-8545 | [email protected]
Frequently Asked Questions
Why is my AC running but not blowing cold air?
The most common causes are a clogged air filter, a frozen evaporator coil, a dirty outdoor condenser coil, or low refrigerant from a leak. Check the filter and the outdoor unit first, since both are free to inspect. If air is moving normally and the outdoor fan is spinning but nothing gets cold, the fault is usually refrigerant-side and needs a technician.
Why is my AC suddenly blowing warm air?
A sudden change usually points to power or a control rather than a slow decline. Check whether a breaker has tripped or the outdoor disconnect has been pulled, confirm the thermostat is on COOL with the fan on AUTO, and look at the outdoor unit. If it hums without the fan turning, that is typically a failed run capacitor and requires a technician.
Can I add refrigerant to my AC myself in Ontario?
No. Under Ontario Regulation 463/10, purchasing and handling refrigerants requires an Ozone Depletion Prevention certificate issued through the Ministry of the Environment, Conservation and Parks. Beyond the legal requirement, refrigerant is not consumed in normal operation, so a low charge always means a leak, and topping it up without repairing the leak wastes the refrigerant and the money.
Why does my AC keep freezing up?
Ice forms when the evaporator coil drops below freezing, which happens when airflow across it is restricted or when refrigerant charge is low. A clogged filter, closed vents, a blocked return or a failing blower all restrict airflow. If the coil refreezes within days of a filter change with all vents open, the cause is charge or a blower fault and needs measurement.
Should I turn off my AC if it is not cooling?
Yes, in several cases. Turn it off if you can see ice, if a breaker has tripped twice, if the outdoor unit hums without the fan spinning, or if you smell burning. Running a system in those conditions can turn a small repair into a compressor or motor replacement. If it is simply cooling weakly with no other symptom, it is safe to leave running while you work through the checks.
How cold should the air from my vents be?
A properly working system typically delivers air about 8 to 11 degrees Celsius cooler than the air returning to it. Measuring the return and supply with a simple thermometer tells you more than touching a vent does. Remember that the system is designed to hold roughly 11 degrees Celsius below outdoor temperature, so on a 35 degree day a 24 degree house is normal performance.
The Bottom Line
Start with the free checks, because airflow problems cause more no-cool calls than anything else and a filter costs a few dollars. The thermostat, the filter, the breaker, the outdoor coil and the vents will resolve a meaningful share of cases before anyone gets paid.
Past that point, the honest answer is that the remaining faults need instruments and, for anything refrigerant-side, a certificate the law requires. Knowing which side of that line you are on is the whole value of this page, and it is why the six checks come before the phone number rather than after it.
Sources and References
- Government of Ontario, certificate to handle refrigerants (Ozone Depletion Prevention certification)
- O. Reg. 463/10, Ozone Depleting Substances and Other Halocarbons, under the Environmental Protection Act
- ENERGY STAR Canada, Natural Resources Canada
- Save on Energy, Home Renovation Savings Program
Related Reading
- What AC repair costs in Mississauga
- Getting your AC ready for summer in Mississauga
- AC energy saving tips for Ontario homes
Regulatory references and refrigerant information verified July 29, 2026, subject to change. This guide is general information, not a substitute for an on-site diagnosis. All amounts in CAD.