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Outside AC Unit Not Turning On: Diagnose & Repair (2024 Guide) (2024)


An outside AC unit that fails to turn on can quickly create a sweltering environment within your home. Common issues like tripped circuit breakers, faulty capacitors, and worn components often prevent exterior AC equipment from activating despite correct thermostat settings. Properly diagnosing and fixing air conditioning problems can save the members of your household from heat exhaustion and prevent damage to belongings that are vulnerable to higher ambient temperatures.

This guide details key troubleshooting steps you can implement before hiring an HVAC company to carry out repairs. 


Reasons Your Outside AC Unit Won’t Turn On

When the inside components, like the thermostat are functioning, but your external AC compressor and condenser fan don’t activate, there are a few possible culprits. Here are the most common reasons an outdoor air conditioner won’t kick on when it should:

The most straightforward reason your outdoor AC won’t turn on is that the dedicated circuit breaker powering the system has tripped. Most external AC components have a circuit breaker in the electrical panel that provides the electricity needed to run.

A tripped breaker doesn’t fully cut power to the unit but does stop it from receiving the juice necessary to turn on and cool your home. Resetting the circuit breaker restores power flow so your outdoor AC can function.

The start capacitor provides the initial jolt of energy to get the compressor motor spinning on startup. It also helps regulate performance. If this AC capacitor fails due to age, sustained wear and tear, or electrical surges, the unit as a whole will fail to activate.

A bulging, cracked, or leaking capacitor needs immediate replacement. Technicians trained in HVAC repair can properly diagnose capacitor issues and swap in a matching replacement.

The contractor acts as the power switch for the condenser unit, telling it when to turn on and off in response to signals from the indoor thermostat. If the contactor malfunctions and fails to close and send voltage to the compressor, the system won’t kick into gear.

The compressor contains parts that generate significant wear and tear over years of cycling on and off. Eventually, components like the pump bearings fail, preventing the system from building and circulating refrigerant pressure to supply cooled air.

If the compressor has failed, installing a new AC unit is the only remedy. A licensed HVAC contractor can test its functionality to determine if replacement is necessary.

Over time, refrigerant leaks can occur due to seal deterioration in valves and lines. Without enough refrigerant, the compressor lacks the pressure and temperature regulation it needs to operate efficiently. Running an AC unit too low on refrigerant can damage its components.

Only trained HVAC technicians using specialized equipment can accurately diagnose low refrigerant issues, locate any leaks, and top up the existing supply if it just needs a recharge.


How to Troubleshoot a Non-Operating AC Unit

Now that you know the most likely reasons why your outdoor air conditioner won’t start, it’s time to troubleshoot and hopefully get it humming along nicely again.

Today’s Homeowner Tips

Caution: Be extremely careful working around electrical components and energized systems to avoid injury risk. If you don’t feel comfortable assessing and repairing issues yourself, hire a trained HVAC technician to service your AC instead.

Follow these troubleshooting steps in order:

Step 1: Check the Breaker

The first step any time an appliance, HVAC system, or other electrical device fails to power on is checking the dedicated circuit breaker in your home’s breaker box.

Locate the double-pole breaker supplying electricity to your outdoor condenser unit. Its label should indicate that it controls your outdoor unit. Flip the breaker fully off and back to the ON position to reset it. Doing so may be enough to restore power so your system fires up when you set your thermostat to activate cooling.

Today’s Homeowner Tips

Call an electrician if the breaker immediately trips again when flipped back on.

Step 2: Inspect the Capacitor

If resetting the circuit breaker doesn’t resolve the issue, next, inspect the capacitor. Before doing anything, turn off the power to your AC at the circuit breaker so you can safely inspect the unit.

Carefully remove the metal covering over the top of the capacitor to expose it.

Look for any signs of bulging, cracks, leaks, or corrosion. Use a multimeter to check microfarads if everything looks visually OK.

Any deviation from factory specs means it’s time to replace the capacitor with an exact replacement match. Technicians have the necessary diagnostic tools and parts to take care of this repair.

Step 3: Check the Voltage at the Contactor

The contactor sits very close to the capacitor. With the breaker still shut off, remove the protective cover so you can access the component. Look to see that all wires are tightly secured in their ports.

Next, turn the breaker back on and carefully check incoming power with a multimeter at the contactor wire connections when your thermostat calls for cooling. If voltage measures low or nonexistent, it likely needs replacement. Again, this fix requires an HVAC technician.

Step 4: Call in an HVAC Service Professional

If you’ve triple-checked the breaker, capacitor, and contactor, but your outside AC unit still refuses to turn on, it’s best to call an experienced technician. There could be complex refrigerant, compressor, or electrical issues at play.

Let the experts troubleshoot the following components:

  • Compressor windings
  • Fan motors
  • Refrigerant pressure
  • Presence of leaks
  • Wiring integrity

Outside AC Unit Repair Costs

The cost to repair an outdoor AC unit that has stopped functioning depends largely on the specific issue present and the parts needing replacement. Minor fixes cost less than significant compressor or condenser repairs.

Here are ballpark AC repair costs, including parts and labor:

Keep in mind those figures reflect repair costs only, assuming the rest of your aging AC system remains in good shape. Should your condenser unit or evaporator coil suffer from significant corrosion or damage, replacement of the entire outside air conditioning system might make more sense.

According to RSMeans national cost data, AC installation can cost anywhere from $470–$7,510. Pricing depends on factors such as system size, efficiency rating, brand, and local energy rebates. However, investing in a unit that’s capable of meeting your home’s needs ensures optimal cooling and adds to the value of your home.


DIY Troubleshooting Vs. Professional AC Repair

When minor yet frustrating issues arise, like a tripped circuit breaker or failing capacitor, DIY troubleshooting offers a more affordable route to get your system running again. Homeowners who know their way around a circuit panel or AC equipment can resolve these basic problems themselves.

As we’ve covered, major system issues often demand expert diagnosis and repair. Technicians undergo vigorous HVAC training and certification programs to work on these complex appliances correctly and safely. They also carry liability insurance that protects your home should anything happen while servicing your unit.

Another perk of professional repair? Many companies offer service warranties on parts and labor ranging from 30 to 60 days. That guarantees the work and gives you peace of mind that someone stands behind the fix.


Maintenance Tips to Prevent Expensive AC Repairs

While even well-maintained AC systems inevitably need service down the line, keeping your home air conditioner in top shape minimizes the likelihood of unexpected breakdowns and major repairs.

Conduct a preseason tune-up and follow these steps to maximize the life span of your outdoor unit:

Dust, debris, and grass clippings easily adhere to condenser coils out in the elements. Regular cleaning improves airflow and efficiency. Hire professionals with high-pressure sprayers and commercial cleaners to deep clean coils or use a basic garden hose DIY approach.

Ensure at least 24 inches of clearance around the entirety of the condenser so airflow isn’t obstructed. The less debris around the unit, the better.

Dirty air filters lead to system strain. Replace disposable filters every three months. Clean reusable options monthly.

Leave refrigerant pressure tests and leak checks to certified technicians with ultra-precise gauges. But do have them assess levels yearly to ensure all is working properly.

Make sure vents and registers inside the home aren’t blocked by furniture, rugs, or drapes that inhibit airflow. Even small obstructions lower AC performance over time.

If your current AC system is more than 10 years old and has required frequent repairs, replacing the entire unit may make sense over continuing to service an aging condenser and evaporator coil. Newer systems prove more reliable and energy efficient, saving on seasonal electricity costs. You can consult installation pros to explore your options.


So, When Should You Call for Professional AC Repair?

While the troubleshooting tips above cover simple steps the average homeowner can try, there are good reasons to call an HVAC company sooner rather than later when your outside unit runs into problems. 

If you’ve worked through the troubleshooting suggestions covered here, but your outdoor air conditioner still won’t turn on, consider hiring. Continuing to flip the power supply on and off can further damage the system.

Getting professional service helps when:

  • Electrical issues pose a safety risk
  • Refrigerant leaks exist
  • Major components like the compressor fail
  • You lack the technical skill for complex repair procedures

Licensed technicians also have access to professional-grade meters, gauges, leak detectors, vacuum pumps, and other diagnostic and repair tools the typical homeowner doesn’t. Plus, companies experienced in AC maintenance know the intricacies and vulnerabilities of these systems best. 

The bottom line? Major AC problems often warrant calling a licensed professional rather than relying on hit-or-miss repairs that can cost you more in the long run. With their advanced equipment, technical expertise, availability of wholesale parts at cost, and added protections of warranties and liability insurance, your AC unit is more likely to receive proper service the first time.


FAQs About AC Units That Won’t Turn On

What should I do if my outside AC unit keeps tripping the breaker?

Frequent breaker tripping signals a serious electrical issue like a short, overloaded circuit or failing capacitor. Each time the system tries to turn on but can’t pull enough power, the breaker overheats and flips off. Call an HVAC technician to inspect the unit and ensure your home’s circuits can safely support its electrical demands.


Why does my outside AC unit only hum but not start?

If you hear a constant humming sound, but cool air isn’t blowing and the fan isn’t spinning, a bad capacitor is most likely preventing the compressor motor from starting. Faulty contactors can cause the same problem. Have an HVAC company test components and supply replacements.


What happens if my AC runs out of refrigerant?

Letting an AC system operate too low on refrigerant can severely damage the compressor. Running it dry also reduces indoor cooling capabilities. Schedule professional recharging services at the first sign of low refrigerant before permanent damage occurs. Annual preventative checks help spot leaks early.


Can I repair my AC unit myself?

Homeowners experienced in using a multimeter to check capacitor charge levels and voltage at the contactor might be capable of performing minor repairs safely.

However, diagnosing complex compressor, condenser, coil, or refrigerant issues requires certifications, in-depth knowledge, specialized tools, and recovery machinery.


How often should AC service be done?

Schedule professional preventative maintenance once yearly before the warmer seasons ramp up. Technicians can deep clean the condenser coil, check refrigerant levels, assess compressor function, inspect electrical contacts, and complete other checks that improve performance and reduce emergency repairs.




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