Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

ac unit not turning on

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

outside ac unit not turning on

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

why is my ac not working

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

ac unit will not turn on

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

outdoor ac unit not turning on

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it. Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker. A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair. A clogged AC drain line can also prevent certain AC units from turning on. Another cause for your AC not working right is a frozen evaporator coil. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

HVAC Troubleshooting

Follow our interactive troubleshooting guide to find answers to your system’s problems.
Choose from a selection of common HVAC issues or pick your product for help with fixes you can try yourself.

AC Not Turning On

You awoke to or came home to a sweltering house. You discover the AC is not turning on. Don’t lose your cool – there may be a simple fix.

Let’s take a look at what might be causing the problem and what you can do when the AC is not working in your house.

Cause #1: Thermostat issues

The first thing to do if your AC is not working is to check your thermostat. If you go to your thermostat and the screen is blank, it may need new batteries. Replace as necessary and consult our thermostat troubleshooting articles.

Make sure you have the thermostat set to COOL and the fan to AUTO. If someone got cold, they may have fiddled with the thermostat settings without you realizing it.

If the thermostat is set to COOL but the AC is not turning on, make sure you have the set temperature lower than the current indoor temperature. If the air still does not come on, the issue is not the thermostat.

Cause # 2: Power issue

Another reason your AC unit is not turning on could be that there is a power issue. Check to see if the indoor shutoff switch is in the ON position. This may look like a light switch if you have a furnace and it is located next to your furnace. You will not see this switch if you have an air handler.

Check your circuit breaker box to ensure that the breaker is not tripped for the indoor OR outdoor unit. If there is a tripped circuit breaker, contact an HVAC professional. Don’t flip the breaker.

The breaker may have tripped due to a serious issue with your HVAC system, and the safest thing is to let an HVAC professional figure out what’s wrong and get your system operating again.

Cause #3: Clogged or dirty air filter

A dirty or clogged HVAC air filter can reduce airflow, making your AC unit work harder than it should. This can lead to a frozen evaporator coil. Check your air filter, and if it’s dirty, replace it. Try turning your AC back on, if it works, you’re in the clear. If it doesn’t, call for AC repair.

Check out our HVAC air filter maintenance guide for some tips.

Cause #4: Clogged AC drain line

A clogged AC drain line can also prevent certain AC units from turning on. As your air conditioner cools it produces condensation. These water droplets drain away from the unit into a drain pan and then away from your home through the AC condensate drain line. A clog in the drain line can cause water damage, or a system shutdown if the unit is equipped with a condensate safety switch.

Cause #5: Frozen evaporator coil

Another cause for your AC not working right is a frozen evaporator coil. The evaporator coil is located indoors next to your furnace. As part of the refrigeration cycle, the evaporator coil gets very cold.

A buildup of dust and debris on the coil can reduce air circulation, causing the coil to frost over. This can then cause the AC unit to shut off. As previously mentioned, a clogged air filter can also cause a frozen coil. If this is the problem, call for AC repair.

Cause #6: Faulty AC capacitor

An AC capacitor is a small part with a big job. Capacitors start your AC unit as well as keep it running. Depending on your air conditioner, it may have both a start capacitor and a run capacitor – or it may have a dual capacitor. If the dual capacitor or start capacitor has gone bad, your AC unit won’t turn on.

The bottom line

You may be able to get the AC working again with a simple tweak, but if those don’t work, we recommend working with an HVAC professional for AC repair. This will help ensure that your central air conditioning system is thoroughly checked out and operating safely.

If your air conditioner is still under warranty, this is also the smart way to go, because DIY repairs could void the warranty.

Air conditioning repair costs can range from $100 to more than $3,000, depending on the issue. If your air conditioner is more than 15 years old and you’re paying more and more for repairs, you may want to think about AC replacement.

Schedule AC repair now

Prevent problems with regular maintenance

Sign up for auto-delivery of air filters, don’t ignore thermostat alerts telling you it’s time to change the filter, download the Trane Home App, set an alert in your phone – whatever it takes, do something so you will remember to change the filter.

Consider signing up for an HVAC service plan with your HVAC company. Standard HVAC maintenance plans include an AC tune-up in the spring and a furnace tune-up in the fall. You may also be eligible for certain perks as a valued customer. This regular maintenance can help catch problems while they’re still small and before they turn into big and costly problems.

Finally, consider opting into Trane Diagnostics. This allows your Trane dealer to monitor your system remotely. They’ll receive alerts of any issues with your system and can act quickly to help you, even when you’re away from home on vacation.

Anne Fonda, Content Writer at Trane Technologies

A Content Writer with Trane Technologies, Anne Fonda researches topics and writes for Trane® and associated residential HVAC brands. She works in collaboration with Trane Technologies subject matter experts, offering easy-to-understand, informative content on complex topics. Her goal is to help consumers make informed decisions on the products and services they need.

She has written for HVAC and other service provider websites for over 16 years. Before transitioning to web content writing, Anne had a 14-year stint as an award-winning journalist. She graduated cum laude from the University of Missouri-Columbia School of Journalism. When she’s not working, Anne enjoys playing word games, reading, gardening, spending time with family, and visiting gardens and museums.

Expert review by Mark Woodruff, Senior Product Manager, Ducted Outdoor