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One of the last problems any homeowner across the GTA wants to deal with during a heat wave is an air conditioner that won't turn on. Unlike AC unit's that are running but not cooling correctly, the inability to start up your cooling system altogether often points deeper electrical issues that need to be addressed promptly by a professional technician. 

When your air conditioner doesn't turn on, it means that your appliance is failing to start its cooling cycle, which is different from when your AC unit is operating, but not cooling. In this type of scenario, the issue is often caused by power-related problems, thermostat miscommunication, safety shut off switches being engaged, or other internal part failures. 

During peak summer months across southern Ontario, when temperatures often rise above 30 Degrees Celsius, having a technician quickly diagnose and repair the problem is essential to your indoor comfort and safety, which is why homeowners are always encouraged to schedule same-day appointments when possible. 

Most times when an AC unit isn't turning on, the underlying reasons can fall into one of two categories. Here is a closer look at what these two categories are, and what usually causes them:

Thermostat, Settings, and Simple Control Problems

• Your thermostat settings may be incorrect.

• You may have dead batteries in your thermostat.

• Thermostat screen may be blank or unresponsive to your requests.

• Your thermostat mode selected is wrong (heat, fan, or off instead of cool).

• The desired temperature you've set is above the current room temperature.

• Smart thermostat programming or Wi-Fi connection errors.

• Loose thermostat wiring or other electrical faults.

• Your thermostat is not communicating with your air conditioner at all.

Power and System Protection Problems

• Tripped circuit breaker box.

• Blown fuses disruption electrical flow.

• Disconnected air conditioner switch from the outlet.

• Electrical panel issues.

• Power loss to the outdoor condenser unit.

• Safety switch has been triggered.

• Float switch has been triggered due to clogged drain line.

Most modern air conditioners include safety features that will shut the unit down is something appears wrong, like water overflowing in the drain pan or electrical power surges. 

Issues with your home's thermostat are one of the main reasons why your AC may not be turning on, but they're often overlooked, even though they may seem like the obvious choice.

Incorrect Settings or Thermostat Failure

• Checking cool mode: Sometimes, a simple switch of your thermostat settings is enough to get your air conditioner back on track.

• Lowering the set temperature several degrees: For your AC to cool, you need to program your thermostat settings to a temperature that is more than five degrees lower than the current room temperature.

• Replacing thermostat batteries: When your thermostat has low batteries, it will have difficulties sending signals to your appliance, which may delay or prevent it from starting up.

• Looking for a blank or flashing display: A blank of flashing display could be due to power issues, wiring problems, or even dead batteries.

• Compatibility issues with newer HVAC systems: If you recently installed a new AC system in your home and your thermostat wasn't updated alongside it, it may not be compatible with your new appliance.

Smart Thermostat and Wiring Issues

• App or schedule overrides that may need manual updates.

• C-wire problems that may need replacement.

• Loss of program settings after a power outage.

• Loose or damaged low-voltage wiring problems.

• Communication errors between your thermostat and air handler. 

Electrical problems are another major cause that could be the culprit behind your AC unit not turning on.

Breakers, Fuses, and Power Supply Issues

• Tripped circuit breaker panel due to electrical overload.

• Outdoor unit breaker is tripped.

• Blown disconnect fuse caused by a power surge.

• Power outages due to severe storms.

• Loose electrical connections.

• Voltage issues affecting your AC unit's start up process.

Failed Capacitors, Contactors, and Components

• Start and capacitor failures

• Contactor is not engaging (dirty coils, thermostat issues).

• Burned wiring or terminals that need replacing.

• Motor failure preventing the unit from turning on.

• Outdoor fan motor issues that restrict airflow.

• Compressor electrical failures. 

Most current air conditioning systems include safety features that automatically shut the system off if water build up is detected. This can be caused by a clogged condensate drain line, a full drain pan that is triggering the float switch, and water leakage in and around your indoor unit. 

Because southern Ontario summers are humid, condensate drain lines can clog a lot easier, which will trigger the float switch. While you can reset your unit and restore cooling in your home temporarily, your unit should undergo a professional inspection regardless. 

Your outdoor unit plays a crucial role in the start up process, and issues that stem from this appliance can prevent your entire system from functioning correctly.

• Your outdoor condenser unit is covered in debris, branches, leaves, or surrounding patio furniture.

• If your cooling system was recently serviced, you may have a disconnected box that's switched off and was never turned back on afterward.

• There may be damage from severe weather conditions like high winds, heavy snow, or rainfall, or wild animals.

• Refrigerant pressure protection lockouts

• Dirty condenser coils or frozen evaporator coils causing the appliance to shutoff and no turn back due to safety concerns.

• Fan motor or compressor damages that may prevent start up. 

Before contacting an HVAC technician for assistance with your air conditioner, there are a couple of troubleshooting and safety checks you can perform:

1. Check settings: Confirm that your thermostat is set to cool.

2. Lower the temperature: Lower your desired temperature below the current room temperature to begin the startup process.

3. Change batteries: Replace thermostat batteries if they are low.

4. Inspect circuit breakers: Check your circuit breakers and reset tripped switches if there are any.

5. Look for outdoor disconnect switch: Inspect the outdoor disconnect switch to confirm whether is has tripped.

6. Check for pooled water: Look for any water around the indoor unit that could suggest a clogged drain pan.

7. Inspect air filter: Check your air filter to see if it needs to be replaced.

8. Open vents: Make sure that your air vents are open and airflow is not restricted.

9. Write down noticed symptoms: Take note of any clicking sounds, humming, or other unusual noises coming from your air conditioner.

10. Check system operation: Identify whether the system is completely dead or partially responsive.

To protect your health and safety, and prevent further damage from occurring to your AC unit, do not do any of the following:

• Do not repeatedly reset the circuit breakers in your home.

• Do not touch the contactor component.

• Do not open sealed electrical panels beyond basic safe checks.

• Do not ignore burning smells.

• Do not continue troubleshooting if wires appear damaged.

• Do not bypass float switches or safety controls.

• Do not attempt refrigerant repairs without proper certifications and licensing. 

Contact a professional HVAC technician when:

• Your circuit breaker keeps tripping.

• Your thermostat has power but your air conditioning system remains off.

• The outdoor unit is humming but does not start up.

• There is a burning smell or buzzing noise present.

• There is water leaking around furnace or air handler unit indoors.

• You believe you're dealing with capacitor, contactor, or motor issues.

• Your air conditioner still will not turn on after basic troubleshooting checks.

• You need electrical testing and further component diagnosis.

Don't delay HVAC service. Waiting to contact a professional technician can cause minor issues to develop into more serious problems that are more damaging and costly to repair. 

Whether you choose to repair or replace your current air conditioning system in your home comes down to a couple of factors:

• Age of the system: If your current unit is nearing the end of its lifespan (between 10-15 years), it may be time to consider an upgrade.

• Frequency of recent breakdowns: Are breakdowns frequent? If so, upgrading to a new appliance can help prevent further breakdowns in the future.

• Cost of major electrical repairs: If repairs are costly and ongoing, it may be more affordable to purchase an entirely new AC unit.

• Compressor replacement considerations: Replacements of compressor components can be costly and close to the cost of installing a new cooling system.

• Older low-efficiency systems: If your current AC unit has a lower efficiency rating compared to new units on the market, repairs may not be worth the investment, as your unit won't be operating at peak performance levels compared even when restored.

• Availability of replacement parts: Depending on the make, model, and brand of AC system, the availability of replacement parts may be limited.

At the end of the day, you'll want to consider your long-term comfort goals and budget. For older units with repeated failures and high repair costs, opting for a new unit makes more sense. In contrast, if your appliance is relatively new, it may be worth going the repair route. 

The best way to prevent air conditioner problems in the future is by doing the following:

• Book a regular maintenance before the summer with a professional technician to identify potential issues before they develop into costly repairs.

• Change dirty air filters regularly (every one to three months).

• Keeping the outdoor unit clean by removing any dirt, debris buildup, and obstructions like branches and leaves from around the unit.

• Checking thermostat batteries periodically to ensure they do not die.

• Clearing the condensate drains and ensure the drain pan is free of debris.

• Pay attention to strange noises and don't delay contacting a technician for a professional inspection. 

Here's a quick comparison table outlining common culprits, signs, and whether or not the issues can be repaired by you, or a professional: