AC Not Turning On? Here’s What to Check First
If your air conditioner won't turn on, there are several safe things you can check before scheduling a repair. Follow the steps below to help determine whether the problem may be related to your thermostat, electrical power, airflow, or the AC system itself.
Common Reasons Your AC Isn’t Turning On
An air conditioner may fail to start for several reasons. Before assuming the system needs a major repair, start with these safe checks to help determine whether the problem is related to the thermostat, electrical power, airflow, or the AC equipment.
1.
Check Your Thermostat Settings
Make sure the thermostat is set to Cool and the temperature is set several degrees below the current room temperature. If the thermostat has a fan setting, use Auto instead of On while troubleshooting.
What to look for: After lowering the temperature, give the system a few minutes to respond. Listen for the indoor equipment and outdoor AC unit to start. If nothing happens, continue to the next check.
2.
Check the Thermostat Display and Batteries
If the thermostat screen is blank or not responding, check whether it uses replaceable batteries. If it does, replace them with fresh batteries and make sure they are installed correctly. Some thermostats receive power directly from the HVAC system and may not use batteries.
What to look for: If the thermostat display comes back on, set it to Cool and lower the temperature several degrees below the room temperature. Give the system a few minutes to respond. If the AC still doesn't start, continue to the next check.
3.
Check Your AC Breakers
Check your home's electrical panel for a tripped breaker. Your air conditioning system may have separate breakers for the indoor equipment and the outdoor AC unit, so check both if they are clearly labeled.
What to look for: If you find a tripped breaker, reset it once. Give the system a few minutes to respond. If the breaker trips again, stop troubleshooting and contact an HVAC professional. Do not repeatedly reset a breaker that continues to trip.
4.
Check the HVAC Power Switch
Many HVAC systems have a power switch located near the indoor equipment that looks similar to a regular light switch. Make sure this switch hasn't accidentally been turned off.
What to look for: If the switch was off, turn it back on and give the system a few minutes to respond to the thermostat. If the switch was already on and the AC still doesn't start, continue to the next check.
5.
Check Whether the Outdoor AC Unit Is Running
With the thermostat set to Cool, safely check the outdoor AC unit from the outside. Listen for the unit running and look through the grille to see whether the fan is operating. Keep your hands and objects away from the unit.
If the indoor system is running but the outdoor unit is completely off, the problem may require further diagnosis. Do not remove electrical panels, reach inside the unit, or attempt to test electrical components.
6.
Check the Air Filter and Airflow
A clogged air filter can restrict airflow through the system and may cause some air conditioners to shut down or stop operating normally. Check the filter and replace it if it is heavily covered with dust or debris. Also make sure the supply vents and return-air grilles aren't blocked.
What to look for: After replacing a dirty filter, give the system several minutes to respond to the thermostat. If the AC still doesn't start, or starts and quickly shuts off again, further troubleshooting may be needed.
When to Stop AC Troubleshooting and Get HVAC Help
Some air conditioning problems should not be handled as a homeowner troubleshooting project. Stop troubleshooting if a breaker repeatedly trips, you notice damaged or exposed wiring, smell burning odors, the system repeatedly starts and stops, or diagnosing the problem would require opening electrical panels or working around electrical components.
If the basic checks above didn't identify the problem, FixWithAPro can help you take the next step. During a live video session, an experienced HVAC technician can review what your AC system is doing, guide you through additional safe checks, and help determine whether the problem requires an in-person HVAC professional.
AC Not Turning On FAQs
Why is my AC not turning on?
Your AC may not turn on because of incorrect thermostat settings, a loss of electrical power, a tripped breaker, a thermostat problem, or an issue with the indoor or outdoor AC equipment.
Why is my thermostat on but my AC isn't running?
If the thermostat is set to Cool and indicates that cooling should be running, but the AC doesn't start, check the HVAC breakers and indoor equipment power switch. If those are on, the system may need further diagnosis.
Why does my AC breaker keep tripping?
A breaker that repeatedly trips may indicate an electrical or equipment problem. Reset a tripped breaker only once. If it trips again, stop troubleshooting and contact an HVAC professional rather than repeatedly resetting it.
When should I call an HVAC professional if my AC won't turn on?
Get professional help if the basic checks don't solve the problem, a breaker repeatedly trips, you notice damaged wiring or burning odors, or diagnosing the problem would require opening electrical panels or working around electrical components.