A non-working outside air conditioning (AC) unit can cause stress, especially when you need cooling in your home on a warm day. From a flipped emergency switch to a more serious issue like a refrigerant leak, there are several reasons your unit might not turn on. While some fixes are simple, others require calling a licensed HVAC professional.
In this guide, we’ll discuss the most common reasons why your outside AC unit isn’t turning on and share tips on how to find the right fix or when to call a technician.
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10 Reasons Why Your Outside AC Unit Isn’t Turning On
A functioning AC unit can feel like it’s essential during the hot summer months. If your outside AC unit isn’t turning on, you’ll want to figure out why and get it working as soon as possible. Here are some possible reasons why your outside AC unit isn’t turning on and some troubleshooting tips.
1. Broken Thermostat
The thermostat controls your home’s temperature. It can’t tell your system when and how long to run if it’s broken. Thermostat replacement is not a do-it-yourself (DIY) job, but a certified HVAC technician can properly install and calibrate the thermostat.
2. The Thermostat Is Not Set To Cool
Check the thermostat to make sure it’s set to “cool.” Someone else in the house may have raised or turned the temperature off. Set the temperature lower than the current house temperature and wait to see if the room cools. If the AC is not cooling, it could be a different problem.
3. The Inside Switch Is Off
Outside AC units typically have a power switch near the attic furnace, closet, or crawl space. This switch looks like a standard light switch, and it’s easy for homeowners to turn it off accidentally. Flipping this switch off turns off the power to the blower, which will power down the outside AC unit.
4. The Shut-Off or Emergency Switch Is Off
Another switch that could cause your outside AC unit not to turn on is the emergency or shut-off switch next to the unit. This switch allows the cooling system to be turned off from the exterior.
Check to see if this switch is in the “on” position. You can also press the reset button on the outside AC unit or use the indoor system to reset the cooling system. After resetting the system, wait and see if the house cools down.
5. There’s a Blown Fuse or Tripped Circuit Breaker
A power surge or an overworked AC unit can trip the circuit breaker or blow a fuse. Go to your home’s main electrical panel and look for a tripped circuit breaker. Turn off tripped breakers and turn them on again. If it trips again after turning it on, you may have an electrical problem that requires an electrician’s help.
Older homes may have a fuse box with a blown fuse that needs replacing. The outside AC unit may also have a shut-off box with a blown fuse inside. In this case, an HVAC contractor may need to replace the fuse.
6. The Air Filter Is Dirty
A dirty air filter causes your air conditioner to run at lower efficiency, increasing your energy bill and keeping your home warmer than it should be. A dirty filter can block airflow to your AC unit, putting more pressure on the system and causing it to overheat and shut down.
Shut the AC unit off and open the access panels to the filter. Remove the old filter and replace it with the correct size and type of air filter. Pay attention to the arrow direction on the sides of the filter. These indicate the direction in which the air is flowing through the unit.
7. The Capacitor Is Malfunctioning
If you hear unusual noises from the outside AC unit and it isn’t turning on, there could be a problem with the capacitor. This happens when the AC condenser tries to spin without power from the capacitor.
To test the capacitor, try carefully spinning the condenser fan with a stick or screwdriver (with the power off). If you have a dual-run capacitor and the fan starts spinning, there may be debris in the motor or internal damage. If the fan doesn’t spin, the capacitor has likely failed and will need replacement. While this is a relatively simple fix, AC capacitor repair costs typically include parts and labor, depending on your system and local rates.
8. Clogged Evaporator Coils
Evaporator coils on an outdoor air conditioning unit get dirty quickly. This makes it difficult for your equipment to transfer heat, so the unit must work harder to keep your home cool. Dirty coils are also prone to corrosion, leading to refrigerant leaks.
This is why it’s essential to have an HVAC contractor clean your AC and perform preventive maintenance every year.
9. There’s a Problem With the Condensate Drain Line
Your air conditioner produces condensation that drains out through a drain line. When there is high humidity, these lines clog more frequently. If this happens, the line trips the safety switch to shut down your AC unit.
10. The Unit Is Low on Refrigerant
Refrigerant is a chemical compound found in copper coils in your outside air conditioning. As warm air moves over the coils, the refrigerant absorbs and cools the heat. If there’s a leak in the coils, refrigerant leaks out, and the AC won’t turn on. Other signs include ice buildup outside the unit, warm air coming from the vents, and unusual noises.
If you suspect a refrigerant leak, only a licensed HVAC technician can repair it and recharge the system. Freon costs can vary depending on the type of refrigerant your system uses and how much is needed to restore proper function.
Safety Guidelines for Checking Your Outside AC Unit
Working on an outside AC unit involves electrical and mechanical risks. Keep these safety tips in mind:
- Turn off the power at the breaker or outdoor shutoff before beginning any inspection.
- Wait 30 minutes after the unit has been running to let the compressor cool.
- Watch out for sharp fins on the coils that can cause injury.
- Avoid contact with wiring and refrigerant lines, especially while the unit runs.
- Wear protective gear, including gloves, goggles, and sturdy footwear.
DIY vs. Professional Outside AC Unit Repair
You can fix some outside AC unit problems yourself, but others require an HVAC contractor’s help. Here are some simple things you can do yourself, and when to call a professional.
DIY Outside AC Unit Repair
Most problems with your outside AC unit aren’t do-it-yourself (DIY) jobs, but there are simple things homeowners can tackle before calling a pro. Here are DIY jobs that most homeowners can do:
- Replacing the air filter
- Flipping tripped circuit breakers on the main electrical panel
- Replacing a blown fuse in the fuse box
- Checking the thermostat to make sure it’s set to cool
- Rinsing the coils on the outdoor central AC unit
- Flipping the power switch
- Hitting the system reset button
Professional Outside AC Unit Repair
Hiring an HVAC technician costs $75–$150 per hour for labor, not including parts. Technicians typically charge $100–$250 for an initial service call. Licensed professionals have the equipment and skills necessary to diagnose and repair complex problems. They can provide a more thorough and accurate diagnosis of any issues and offer targeted solutions. EPA regulations require a licensed technician to handle refrigerant and electrical components.
How To Hire a Professional for Your Outside AC Unit
You must hire an HVAC technician when your AC requires more than a simple DIY repair. When you review candidates, keep these tips in mind.
- Start your search for an HVAC professional by researching potential contractors in your area online and reading reviews and ratings from past customers.
- Look for contractors with specific experience working on outside AC units, and ask for references from previous clients.
- Check that the HVAC contractor is licensed, certified, and insured and verify their credentials with the state licensing board.
- Ask for a detailed estimate and don’t hesitate to get several quotes.
- Ask about warranties and guarantees on workmanship.
Preventive Maintenance Tips for Your Outside AC Unit
Performing routine maintenance on your outside AC unit can help keep it running efficiently, prevent costly repairs, and extend its lifespan. Here are some key tips:
- Consult your unit’s manual for model-specific maintenance instructions.
- Check the fan blades and replace broken or missing parts to keep air flowing efficiently.
- Clear the air ducts and vents to make sure airflow isn’t blocked by debris or furniture.
- Flush the drain line monthly to prevent mold or clogs from excess condensation.
- Schedule seasonal tune-ups so a professional can perform HVAC maintenance before peak usage to help prevent breakdowns.
- Inspect belts, pulleys, seals, and joints and look for wear or damage that could reduce efficiency.
- Keep your thermostat working by replacing the batteries as needed and setting it for optimal efficiency.
- Monitor refrigerant levels and call a pro if refrigerant levels are low or you notice signs of a leak.
- Replace air filters regularly as dirty filters can reduce airflow and system performance.
- Seal windows and doors, which keeps cool air inside and prevent unnecessary strain on your unit.
Our Conclusion
There are several possible reasons why your outside AC unit isn’t turning on. Some issues may be resolved with simple DIY troubleshooting, while others require the expertise of a licensed HVAC technician. If your system needs major repairs or replacement, it’s also important to consider potential HVAC installation costs. We recommend requesting quotes from at least three reputable contractors to compare services, pricing, and warranties before deciding.
FAQs About An Outside AC Unit Not Turning On
Why is my outside AC unit not turning on?
If your outside AC unit isn’t turning on, troubleshoot the problem by checking the circuit breaker, ensuring the shut-off or emergency switch wasn’t flipped, and resetting the system. If that doesn’t work, call a professional HVAC company to diagnose and fix the problem.
Is there a reset button on my outside AC unit?
Some outside AC units have a small red reset button. You can learn more from your HVAC manufacturer if you can’t find the button.
How do I know if my outside AC fuse is blown?
If you suspect your outside AC fuse is blown, use a multimeter or voltmeter to test the component. If it doesn’t get a reading, the fuse is blown.
Can you replace just the outside AC unit?
It’s typically recommended to replace both the indoor and outdoor AC units at the same time. This is because a new outdoor unit may not be compatible with the old indoor unit. Replacing only one could also void the warranty.
