With recent heat warnings in the area and more hot days in the forecast, many London homeowners are asking the same question:
“Is my AC just working hard because of the heat, or is something wrong?”
That is an important question. During a heatwave, it can be normal for your air conditioner to run longer than usual. But if your home still feels warm, the airflow feels weak, or your AC is blowing warm air, there may be a real cooling problem that needs attention.
This guide explains what can be normal during extreme heat, what you can safely check yourself, and when it may be time to call Aire One, a trusted HVAC company in London.
For the latest local weather conditions and forecast updates, you can check the Environment Canada London forecast.
Why Your AC Works Harder During a Heatwave
Your air conditioner does more than blow cold air. It removes heat and humidity from your indoor air and moves that heat outside. During a regular summer day, this process is usually manageable. During a heatwave, your AC has to fight several things at once:
- Outdoor temperatures stay high for many hours
- Humidity makes the air feel warmer and heavier
- Sun-facing rooms gain heat through windows and walls
- Attics and upper floors hold more heat
- Your system may run for longer cycles with fewer breaks
- Dirty filters, blocked vents, or outdoor debris can reduce airflow
In other words, even a working air conditioner can feel under pressure during several hot days in a row. But there is a difference between “working hard” and “not working properly.”
What’s Normal When Your AC Runs During a Heatwave?
During a heatwave, these situations may be normal, especially in the afternoon and early evening.
Your AC Runs Longer Than Usual
If your air conditioner is running more often during very hot weather, that does not always mean it is broken. Your system may need longer cycles to remove heat from your home, especially if the outdoor temperature and humidex are high.
The Upstairs Feels Warmer Than the Main Floor
Warm air rises. Bedrooms, upper floors, loft areas, and rooms above garages often feel warmer than the main level. This is especially common in older homes, homes with limited insulation, or houses with large sun-facing windows.
Your Home Cools Slowly During the Hottest Part of the Day
If the afternoon sun is strong, your AC may cool more slowly than it does in the morning or at night. A one- or two-degree difference during peak heat can happen, especially if doors are opening often or blinds are left open.
The System Runs More Often After Cooking, Laundry, or Heavy Indoor Activity
Using the oven, dryer, many electronics, or bright indoor lighting can add heat inside the house. During a heatwave, these smaller heat sources can make your AC work even harder.
What Is Not Normal?
Some AC symptoms should not be ignored. If you notice any of the following, your system may need professional service.
1. Warm Air Coming From the Vents
If the thermostat is set to cooling but the vents are blowing warm or room-temperature air, something may be wrong. Possible causes include low refrigerant, a frozen coil, a dirty coil, an electrical issue, or a problem with the outdoor unit.
2. Weak Airflow
Weak airflow can make your home feel warm even if the AC is producing cool air. This may be caused by a clogged air filter, blocked return vents, duct issues, blower motor problems, or a frozen evaporator coil.
3. Ice on the AC Line or Indoor Coil
Ice is not a sign that your AC is “extra cold.” It usually means airflow or refrigerant problems. If you see ice on the refrigerant line or around the indoor coil area, turn the system off and call for service. Running the system while it is frozen can make the problem worse.
4. The AC Turns On and Off Too Quickly
Short cycling means the AC starts, runs for a short time, shuts off, and then starts again. This can happen because of thermostat issues, electrical problems, refrigerant problems, an oversized system, or overheating components.
5. The Outdoor Unit Is Not Running
If your indoor fan is blowing but the outdoor condenser is not running, your AC cannot properly remove heat from the home. This may point to a capacitor, contactor, electrical, thermostat, or compressor-related issue.
6. Strange Noises or Smells
Grinding, buzzing, rattling, burning smells, musty odours, or chemical-like smells should be checked. These can point to loose parts, motor problems, electrical issues, water buildup, or refrigerant concerns.
7. Your Home Keeps Getting Warmer
If your indoor temperature keeps climbing even while the AC is running, the system is not keeping up. During extreme heat, a small delay can happen. But if the home never cools down, or the temperature rises hour after hour, it is time to look deeper.
If this sounds familiar, you may need AC repair in London before the problem becomes more serious.
Safe Things to Check Before Calling for AC Repair
Before booking service, there are a few safe checks homeowners can do. These steps will not fix every issue, but they can help you rule out simple problems.
Check Your Thermostat Settings
Make sure the thermostat is set to “Cool,” not just “Fan.” Also check that the temperature is set lower than the current indoor temperature.
Avoid setting the thermostat extremely low, such as 16°C or 17°C, hoping the home will cool faster. Your AC does not cool faster because the number is lower. It simply runs longer, which can add more strain during a heatwave.
A steady, realistic setting is usually better than constantly changing the temperature.
Replace or Check the Air Filter
A dirty air filter is one of the most common reasons for weak airflow and poor cooling. During heavy cooling months, filters can clog faster than expected.
ENERGY STAR recommends checking filters monthly during heavy-use seasons and changing them when dirty. A dirty filter slows airflow and makes the system work harder, which can waste energy and increase the risk of system problems.
Make Sure Vents and Returns Are Open
Walk through your home and check supply vents and return air grilles. Make sure they are not blocked by furniture, rugs, curtains, laundry baskets, or storage boxes.
Your AC needs good airflow to cool properly. Blocking vents can create uneven temperatures and add pressure to the system.
Look Around the Outdoor Unit
Your outdoor unit needs space to release heat. Check for leaves, grass clippings, weeds, branches, or objects around the condenser.
Do not open the unit or touch electrical components. But you can safely clear light debris around it and make sure there is open space for airflow.
Keep Blinds and Curtains Closed During Peak Sun
Windows can add a lot of heat to the home. During the hottest part of the day, close blinds or curtains on sun-facing windows, especially in bedrooms, living rooms, and upper floors.
This simple step can reduce heat gain and help your AC work more effectively.
Avoid Adding Extra Heat Indoors
During a heatwave, try to avoid using the oven, dryer, or other heat-producing appliances during peak afternoon hours. Cooking outside, using smaller appliances, or running laundry later in the evening can help reduce indoor heat buildup.
Use Fans the Right Way
Ceiling fans and portable fans can help move air and make rooms feel more comfortable. But fans do not actually lower the room temperature. They cool people, not rooms.
Turn fans off when rooms are empty to avoid wasting electricity.
When Should You Call a Professional?
You should call for AC service if:
- The AC is blowing warm air
- Airflow is weak even after changing the filter
- The outdoor unit is not running
- Ice appears on the refrigerant line or coil
- The system keeps turning on and off quickly
- The breaker trips repeatedly
- There are unusual noises or burning smells
- Water is leaking around the indoor unit
- Your home keeps getting warmer while the AC runs
A trained technician can check the full system, including airflow, refrigerant levels, electrical components, thermostat operation, the blower motor, evaporator coil, condenser coil, capacitor, contactor, drain line, and overall system performance.
Aire One provides complete cooling services in London, including AC diagnostics, repairs, maintenance, and emergency support.
Why You Should Not Ignore AC Problems During a Heatwave
When the weather is mild, a small AC issue may not feel urgent. During a heatwave, that same issue can quickly become a bigger problem.
For example, a dirty filter can reduce airflow. Reduced airflow can cause the coil to get too cold. That can lead to ice buildup. Once the coil freezes, your AC may stop cooling properly. If the system keeps running while frozen, it can place more stress on the compressor and other components.
Small problems can also affect comfort, indoor humidity, and energy use. If your system is running constantly but not cooling well, you may be using more electricity without getting the comfort you need.
Indoor Heat Is More Than a Comfort Issue
Extreme indoor heat can be a health concern, especially for older adults, young children, people with medical conditions, and anyone without reliable cooling. Health Canada recommends an upper indoor temperature limit of 26°C to help protect older adults from heat-related illness.
If your home is getting too warm and your AC is not keeping up, take it seriously. Check on family members, neighbours, and vulnerable people during hot weather. If someone shows signs of heat illness, follow public health guidance and seek medical help when needed.
Should You Repair or Replace Your AC?
Not every AC problem means you need a new system. Many cooling issues can be repaired, especially if the system is generally in good condition.
Repair may make sense when:
- The AC is not very old
- The issue is isolated
- The system has been maintained
- The repair cost is reasonable
- The AC usually cools the home well
Replacement may be worth discussing when:
- The AC is older and breaking down often
- Repair costs are becoming frequent
- The system uses a lot of energy
- Cooling is uneven throughout the home
- The system is too small or too large for the house
- Major components are failing
A professional inspection can help you make the right decision based on the condition of your system, your home, and your comfort needs.
How to Help Your AC Before the Next Hot Day
Once your AC is working properly, a few habits can help reduce strain during the next stretch of hot weather:
- Replace or check your filter regularly
- Keep outdoor equipment clear of debris
- Keep vents and returns open
- Close blinds during peak sun
- Use ceiling fans to improve comfort
- Avoid large thermostat setbacks during extreme heat
- Schedule maintenance before peak cooling season
- Pay attention to new noises, smells, or cooling changes
Natural Resources Canada also provides helpful information about selecting, operating, and maintaining cooling systems in its guide to air conditioning your home.
Need AC Repair in London, Ontario?
If your air conditioner is running but your home still feels warm, do not wait until the system stops completely. A heatwave can put extra stress on your AC, and small problems can become bigger when the system is working nonstop.
Aire One Heating & Cooling London provides trusted AC repair in London, including diagnostics, repairs, maintenance, and emergency cooling support.
Book your service online or contact Aire One today to keep your home cool, safe, and comfortable during hot summer weather.
FAQ: AC Problems During a London, Ontario Heatwave
Is it normal for my AC to run all day during a heatwave?
It can be normal for an AC to run longer during very hot and humid weather. However, if it runs all day and your home still feels warm, or if the air from the vents is not cool, there may be a problem.
Why is my AC blowing cool air but my house is still warm?
This can happen because of weak airflow, poor insulation, dirty filters, blocked vents, duct issues, high humidity, or an AC system that is struggling under extreme heat. If the temperature keeps rising indoors, it should be checked.
Can a dirty filter really stop my AC from cooling?
Yes. A dirty filter can restrict airflow, make the system work harder, reduce comfort, and contribute to frozen coils or other problems. Checking the filter is one of the first things homeowners should do.
Why is my upstairs hotter than downstairs?
Upper floors naturally collect more heat. Poor attic insulation, sun exposure, closed vents, duct design, or weak airflow can make the problem worse.
Should I turn my AC off when I leave home?
During a heatwave, turning the AC completely off can allow the home to heat up too much, making it harder to cool later. A moderate temperature adjustment is usually better than shutting the system off completely.
When should I call for AC repair?
Call for service if your AC is blowing warm air, airflow is weak, ice is forming, the outdoor unit is not running, the system is making unusual noises, or your home keeps getting warmer while the AC runs.
