It’s the middle of summer, temperatures are sweltering, and you set your thermostat to activate the air conditioner for some much needed cooling relief. But even though the thermostat is calling for the AC to turn on, nothing happens. No cold air comes blowing out of the vents. Frustrating, right?
When your AC fails to start up and provide cooling when the thermostat calls for it, there are a few common culprits to check before you shell out money for professional repairs. With some basic troubleshooting, you can get to the bottom of why your air conditioner isn’t kicking on and potentially fix the issue yourself. Let’s walk through the steps.
Check Your Thermostat Settings
Before you assume there’s something broken with your actual AC unit, double check that the thermostat is setup properly. Here are some things to verify:
- Make sure the thermostat mode is set to “cool” and not “heat” or “auto”. If it’s on auto, the system will only run the AC when the indoor temperature rises above the defined limit.
- Confirm that the desired set temperature on the thermostat is lower than the current room temperature. If set higher, the AC won’t turn on.
- Ensure the thermostat has power and is not malfunctioning itself. Try resetting it by turning the power off and back on.
- If using a “smart” internet connected thermostat, check that the wifi connection is working properly.
Taking a minute to double check the thermostat settings could reveal an easy fix and get your AC running without any major intervention required.
Inspect Air Filters for Restricted Airflow
One of the most common reasons an AC won’t start up when cooling is called for is a blocked airflow path due to a dirty filter. Air filters trap dust, pollen and other particles as air passes through the HVAC system. Over time, they become clogged and restrictive.
To check your filter, locate the access panel on or near the furnace/AC indoor unit and pull out the filter. Look for dirt buildup on the mesh material. If very dirty, replace it with a new filter of the same size. Even if not excessively dirty, changing filters every 3 months helps prevent restricted airflow issues.
With clean, unobstructed airflow, your AC will be able to turn on and deliver cold conditioned air when the thermostat calls for cooling. So be sure to inspect the filter if you’re encountering a no cooling issue.
Reset the Electrical Circuit Breakers
For any appliance in your home, an interruption of power can prevent normal operation. Air conditioners are no exception. A tripped circuit breaker that cuts electricity supply to your AC unit is one possibility for why it fails to start up when cooling is called for.
Find the main electrical service panel, which will look like a gray metal box on the interior or exterior wall. Open the front cover. Locate the circuit breaker switch labeled for the air conditioner/furnace and flip it fully off and then back on. This reset will reconnect power to the AC system.
Circuit breakers trip when too much current flows through the circuit. With the power reset, check your AC operation again. If the circuit trips again shortly after, contact an electrician to inspect for any wiring issues.
Examine the Ignition System
In a furnace/AC combo system, the air conditioner uses the furnace’s blower motor fan to distribute the cool air. But for the furnace blower to operate, the ignition sequence must activate first when cooling is called for. This is where problems can occur.
Within the furnace is an ignitor, which creates a spark to light the furnace’s gas burner on demand. If the ignitor is dirty, worn out, or defective, it will fail to spark and thus prevent the blower from starting up to deliver cooled air. Professional HVAC technicians have tools to diagnose ignition system issues and replace the ignitor if faulty.
Test the Capacitor
Here’s another possible culprit if your outdoor AC compressor unit won’t turn on when the thermostat calls for cooling. Capacitors are electrical components that store and release energy as needed to start up the compressor. A failed capacitor can prevent the compressor motor from starting.
Warning signs of a bad capacitor include a buzzing or humming noise coming from the outdoor unit but no startup. When testing capacitors, HVAC techs check the microfarad (uF) rating for accuracy. If the capacitor is found to be defective, replacing it with a properly matched working model should get your AC running again.
Check Control and Power Wiring Connections
The electrical control wires that run between your indoor thermostat and the furnace/AC components allow communication signals to be sent when cooling operation is needed. If the wiring becomes damaged or disconnected, those signals can’t get through.
Some things that can damage thermostat wiring include rodents chewing on wires, accidental breaking or pulling during maintenance, corrosion from moisture, and loose wire terminal connections. HVAC technicians have the tools to test for wiring continuity and locate any breaks that need repairing.
Call an HVAC Technician for Complex Issues
While many “AC won’t turn on” problems arise from fairly simple things like dirty filters or tripped breakers, there are some issues only a professional technician can accurately analyze and fix. Electrical control boards, bad contactors, low refrigerant, and blower motor failures require specialized diagnostic skills.
If you’ve checked the basics covered in this article but your AC still refuses to start up when the thermostat calls for cooling, it’s best to call in an HVAC company. With their technical expertise and proper equipment, they can get to the root of the problem and get your system back to pumping out crisp, cool air.
Prevent Future Air Conditioning Breakdowns
While HVAC systems can certainly fail without much warning, taking proactive maintenance steps will help minimize issues:
- Replace air filters regularly every 3 months to maintain airflow.
- Have a professional perform annual tune-ups to inspect all AC components.
- Learn how to safely hose down the condenser coils when they get caked with debris.
- Clear any vegetation or other obstructions away from the outdoor AC unit.
Your air conditioner works hard to keep you comfortable. Show it some TLC and it will be ready to cool your home when those long hot summer days arrive.
As we’ve covered, a wide array of issues can cause an air conditioner to not turn on when the thermostat calls for cooling. But rather than burning up from the heat while you puzzle over what’s wrong, just focus on the solution. Start with the simple DIY troubleshooting tips above. But if your AC still refuses to start up, bite the bullet and call an HVAC technician. With their expertise, they’ll have your system up and running cool in no time.
