Outside AC Unit Not Turning On

Outside AC Unit Not Turning On

Anthony Barnes

Need to Hire a Plumber?
Get a free estimate online from top local home service pros in your area.
Note: This post may contain affiliate links. This means that at no cost to you, we may receive a small commission for made purchases.

So you have checked the inside AC unit and it looks to be working fine yet the outside AC unit simply is not running. With a split-system AC unit, you effectively get two parts and if either the outside or inside the unit is not working then this will affect the entire air conditioning system. 

There are several reasons why the outside AC unit may not be turning on but it can prove simple to find out the cause of the problem and resolve it. 

In this guide, we will look at the ways to find out why your outside AC (see also ‘Fixing Your Clogged AC Drain Pipe Without A Fuss‘) unit may not be turning on and how you can easily turn it back on.

Outside AC Unit

How To Find Out Why Your Outside AC Unit May Not Be Turning On

Before you contact a qualified HVAC technician, you can try to troubleshoot why your outside AC unit may not be turning on. 

Check The Condensate Drain Line

A properly functioning AC unit creates condensation which then drains out through… its drain line. However, during summer when it can become excessively humid the condensate drain line can become clogged

As a series of events, this can then lead to the safety switch tripping which then shuts down the entire cooling system. You could use a dry/wet vacuum to attempt to suck up the blockage and clear up any clogging. 

Blown Fuse/Tripped Circuit Breaker

A power surge can always knock out various appliances as well as blow a fuse or trip a circuit breaker. Not only will your AC unit be disrupted but so will several other electrical appliances in your home. 

To check, locate the circuit panel in your home (this may be a fuse box in an older house) and see if you can spot a blown fuse that can be simply replaced. With a circuit breaker, it may take a bit longer to find a tripped circuit, but you can flip the switch from ‘off’ to on’ and that may solve the problem. 

A blown fuse may even have occurred at the safety shut-off box which can also result in the AC unit not turning itself on. Locate your AC unit and the safety shut-off box should be nearby which you can open up to check for a blown fuse. 

Again, simply replace the problematic fuse and that should solve the problem. The fuse may not even appear to be damaged significantly but once replaced the unit may return to working order, if it does not, you can call in an air conditioning specialist. 

Check The Power Switch

If everything looks as it should with your indoor system, you can check the power switch which is found near your heating, ventilation, and air conditioning (HVAC) system. First, turn the AC unit off then check if the power switch on your HVAC system is ‘off’ or ‘on’.

This power switch is typically found in a closet, the attic, or a crawl space that exists close to your system. 

The power switch can look just like a light switch and so it is very easy to simply turn it off which can cause the indoor system to freeze and the whole AC system will be powered down.

Turn it back to ‘on’ and this could get the unit back running though you should explain to the other members of the household what the switch is for before this happens again.

Check The Shut Off Switch

A lot of AC units also have a shut-off switch (it can also be called an emergency switch) which can be found close to the outdoor system in a metal box that is attached to the outside of your home. 

Sometimes a failure for the AC unit to turn itself on is down to this unit’s shut-off switch being in the ‘off’ position. While this switch is harder to accidentally turn off than the power switch inside your home, it can still occur following a regular servicing so turn it back on and that may solve the problem. 

Check The Thermostat

If you have mischievous children in your home or someone has accidentally pressed the wrong setting on the AC unit, it could be set to cool. Should you want your AC unit to project cold air then you would typically set it to the ‘cool’ setting but not when you want it to warm up your home. 

To check the AC unit is working as it should turn down the temperature on the thermostat by around five degrees and hopefully, you hear the AC power itself on to confirm that the system is back up and running.

A Failing Capacitor

A Failing Capacitor

An outside AC unit is typically powered by a capacitor and if this is failing then the AC unit itself will fail too. You may even hear this problem as a buzzing sound emanating from the outside AC unit as the condenser fan tries to spin without any power coming from the capacitor. 

There are two capacitors in an AC unit which are the start capacitor and the run capacitor. The run capacitor could be a single run or a dual run type while the start capacitor effectively starts the condenser fan by initially pushing it. 

Both the start and run capacitor can gradually deteriorate over time which can be a result of power surges and even being overworked. There is a simple test to see if you restart the condenser fan and requires a thin piece of wood to push it along. 

If the fan inside the AC unit (see also ‘AC Unit Frozen? | Common Reasons And Troubleshooting Tips’) still fails to move then the capacitor may need to be replaced. However, if the fan does start to spin then this may indicate a buildup of dust or debris inside the AC unit’s fan motor that has even damaged it. In either case, you should call out an air conditioning specialist to take a look.

Low Freon

If your outside AC unit is running low on Freon then that may mean it fails to turn itself on. Freon is a vital substance that the AC unit uses as a chemical refrigerant to cool down warm air which comes from the outside before it comes into the home. 

If there is a leak inside your unit, the Freon can run low and the AC unit can stop working. You may see some frost building up on the outside AC unit or be able to tell that this is the problem as purely warm air comes out of the vents. 

If you can hear a hissing sound coming from near the outside AC unit then this may indicate a problematic leak. Freon can be a dangerous substance to come into contact with so if this is the problem then you may need to contact the Environmental Protection Agency (EPA) (see also ‘What Does It Mean To Be EPA Certified?‘) to handle it as it will require a licensed professional.

How To Turn Your Outside AC Unit Back On 

Once you have established the reason why your outside AC unit (see also ‘Should I Cover My A/C Unit In The Winter?‘) may not be turning itself on, it should be relatively straightforward to turn it back on. If it still fails to turn itself back on then there are some simple steps you can take to get it back working again.

System Reset

This is typically a really simple method to restart the AC unit and is the equivalent of switching your computer off and back on again to see if it solves the problem. Locate the cooling system and look for the ‘reset’ switch then give it a push to see if the system turns off and then back on.

This may not be possible if your cooling system does not have a specific ‘reset’ switch, in which case you can perform a manual restart by turning off the AC unit via the thermostat and then giving it five minutes before you turn it back on. 

It may be surprising but this simple resetting of the cooling system could solve the problem without any further investigation. 

Call An AC Specialist

If you have exhausted all the possible options and the outside AC unit is still not working then you can call an AC professional. They should have some specialist equipment and some experience in how to fix the problem. 

The AC professional should be able to solve the problem swiftly though may recommend that you will have to buy a replacement unit instead. Whichever decision you make, you should schedule some regular servicing and maintenance to ensure the problem does not recur. 

Final Thoughts

Several reasons may be the primary cause of why your outside AC unit fails to turn itself on. Thankfully, there are various ways to troubleshoot the problem and you can even solve it yourself.

If you have run through the list of possible reasons why the fault occurs and you still cannot work out what is going wrong then it may be time to consult an air conditioning specialist.

Frequently Asked Questions

How Do I Know If I Need To Replace My AC Fan Motor?

There can be several telltale signs that it is time to replace your AC fan motor. These can include a failure for the AC fan to start at all, the AC fan does not stop running, or the blades of the fan are rotating very slowly.

You can also hear a problem with the AC fan motor if it rattles, hums, or buzzes. It can also produce a solely cold airflow when it should be warm or runs intermittently.   

What Is An Easy Way To Tell That The AC Fan Motor Is Working Properly?

If you can hear a pleasant humming sound coming from your outside AC unit then this is usually a good sign that the fan motor is working as it should. Check the vents at the top of the unit and the fan blades should also be rotating smoothly. 

Need to Hire a Plumber?
Get a free estimate online from top local home service pros in your area.

Recent posts

Need help with a repair or install?

Free Online Quote

By Anthony Barnes

Anthony Barnes is the founder of Water Heater Hub and a second-generation plumber by profession. Before developing Water Heater Hub, Anthony Barnes was a full-time plumber, and he has undertaken a wide variety of projects over the decades. As a second-generation plumber, it was easy for Anthony to get used to the technicalities of all from a tender age