11 Reasons For AC Not Turning On and How To Fix Your Air Conditioner

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Is your air conditioning unit on strike and not turning on? An array of reasons could be behind this sudden failure to launch, with some easier to repair than others. Here are the 11 most common problems for your AC not turning on (plus how to fix them).

1. Thermostat Malfunctioning

a person turning on the thermostat

Thermostat malfunctioning is one of the most common culprits behind air conditioner issues. Your air conditioner might go on strike abruptly in the middle of the summer, giving no apparent reasons why it stopped working. But before you begin sleuthing in search of the air conditioning culprit, check for thermostat issues first. 

The batteries could be dead (if applicable), or the thermostat could be off entirely. If either of these factors is the issue, the system can’t signal the AC to turn on. So, start by checking the thermostat. 

  1. Ensure the display is on; if it is not, turn it on and check the AC is on.
  2. If the display doesn’t turn on, check the batteries. Replace the batteries with a completely new set, then check for proper air conditioning function. 

In some cases, the temperature setting is too high, so the thermostat never tells the AC to kick on as the temperature in your home doesn’t get low enough.

Note: If you do not notice any changes after switching on the display or replacing the batteries, lower the temperature setting by five or six degrees. Wait a few minutes to see if the air conditioner kicks on. 

If the air conditioning still doesn’t start, look for debris and corrosion within the thermostat itself. Alternatively, check for blown fuses or loose screws and wires in the thermostat. If you find electrical issues, it’s usually best to pass them on to a professional.

2. AC Circuit Breaker Tripped

homeowner turning on the AC circuit breaker

In some cases, the air conditioning problem lies away from the thermostat and AC system itself. Instead of something within the system failing, the culprit could be the circuit breaker for your AC unit. When the circuit breaker supplying power to the air conditioner trips, it won’t provide the power necessary to turn the air conditioner on. 

So, check your circuit board if your AC system offers no response whatsoever. Generally, you can find the correct circuit breaker that powers the AC in your home’s breaker box or control panel. Each breaker should be labeled. If the AC breaker is tripped, reset it and wait a few minutes before turning the AC unit on. 

Note: If the breaker continually trips, do not keep resetting it, as this indicates a high voltage problem that could lead to an electrical fire. This problem is more serious, so you’ll need the help of an HVAC pro specializing in air conditioning repair.

3. Clogged Air Filter

homeowner removing a dirty air filter

The sole function of the filters is to remove gunk and ensure proper air circulation. When they become clogged with debris, the air circulation slows to a near halt, causing issues for your AC unit. 

If the blockage is bad enough, your air conditioner will have to work overtime to try to cool your home, and when this happens for a while, it can prevent the AC from working entirely.

A dirty air filter can actually freeze the AC system’s outdoor unit, which obviously causes issues for the system as a whole. Plus, it reduces your home’s indoor air quality, which is not something you want to deal with. 

So, if you can not remember the last time you cleaned or replaced your AC system’s air filters, this is what you should check next.  For information on the correct replacement size, see your manual, information guide, or label on your unit. Or get the sizing information from your existing one. 

Remove it and clean or replace it as necessary. If the unit is frozen, wait until the air conditioner unit thaws before you switch it back on.

4. Shut Off Switch Turned Off

The indoor shut-off switch might be off, preventing the system from kicking on as it needs to. While it might seem like an apparent reason, you might unintentionally turn this switch off, as it can easily be mistaken for a light switch. 

The shut-off switch is usually located near the furnace or in a closet, attic, or crawl space. Search these areas for the switch, and once you find it, ensure it’s in the “ON” position. If not, switch it back on. While you’re at it, it does not hurt to label the switch for future reference, so you don’t shut it off by accident again.

5. AC Condenser Unit Unplugged

outdoor AC condenser units plugged in

Sometimes, the problem is as simple as an unplugged AC unit. If the AC system isn’t plugged in, it won’t be able to draw power to boot up the system, effectively preventing it from powering on. So, before you get too far, check the AC condenser unit and ensure it is not unplugged. 

While you check the power cord to ensure it isn’t unplugged, examine it for damage. Check for frays or general wear and tear, as these factors could cause issues with the cord and prevent it from functioning correctly.

Alternatively, the not turning on issue could lie with the outlet itself. You can check the outlet using a multimeter, but if you do not have one, you can have an electrician test the outlet for you. 

Note: If the power cord is damaged, consult an HVAC technician for the next steps. If you suspect the outlet is faulty or see disconnected or loose wires, avoid tinkering with it, as doing so can be hazardous. Instead, seek the help of a professional electrician.

6. Air Conditioner Unit has a Refrigerant Leak

HVAC technician checking for refrigerant leak

All air conditioners use refrigerant to cool the warm air it pulls through the unit. The refrigerant is stored inside the AC unit’s coils and effectively chills the air as it moves over them.  Without refrigerant, the air conditioning will not be able to function correctly. Unfortunately, you can’t simply add more refrigerant. 

If your air conditioner is low on refrigerant, it has a leak. Air conditioners aren’t designed to consume refrigerant, so they shouldn’t need regular refills or have refrigerant shortages. Given the nature of refrigerant, it’s best to call an EPA-certified HVAC professional for service. They’ll need to examine the HVAC unit for leaks, repair the damage, and recharge it to the correct level. 

Note: Cracks can develop over time throughout the system, allowing refrigerant to seep through areas it shouldn’t. Or, corrosion due to lack of routine maintenance can have the same effect.

7. Frozen Coils 

If your air conditioner’s coils freeze, the unit likely won’t switch on. Generally, this problem goes hand-in-hand with a dirty or clogged air filter, but it can also result from other airflow issues (like clogged ductwork). 

The outdoor unit has the AC system’s compressor, while the indoor unit houses the evaporator coil. There’s a refrigerant line extending between the two, and when functioning properly, things can move as needed. However, when airflow through the system is limited, warm air from your home can’t reach the refrigerant. 

This causes the refrigerant to become too cold and promptly freezes any residual moisture on the coils. If the coils are frozen, you’ll need to find the root cause. In many cases, the issue lies within the air filters, but if you have already cleaned those, check the ductwork. 

Once you determine the cause and remedy the issue, let the HVAC coils defrost before starting the system again. Since the ice will melt as the coils warm up, use something to collect the water (towel, pan, etc.).

8. AC Capacitor Fault

HVAC technician checking the AC capacitor

The capacitor in an AC unit serves a critical role: it connects to the circuit in the motor, giving the motor the necessary kick to start the cycle. Once the motor reaches a specific speed, the capacitor disconnects from the circuit and allows the cycle to run. 

This part of the system is sensitive to heat, so when your AC system works overtime in the summer heat, it can cause the capacitor to overheat. Alternatively, the AC unit’s capacitor may fail after overworking as the system attempts to cool your home to the lowest temperature on a scorching day. Or the capacitor could just be faulty from a defect or an impact. 

Some occurrences, like power outages or fluctuations, can also affect the capacitor. While you can’t control these situations, you can install preventative measures, like a surge protector. 

If the capacitor fails, the system won’t turn on, and you might hear clicking noises from the outdoor unit. So, if your AC unit won’t turn on, you’ll need to replace it, which is a job best left to the HVAC professionals.

9. Condenser Unit Needs Cleaning

If the outdoor part of your AC unit isn’t turning on, there’s a chance your condenser is in dire need of a thorough cleaning. The outdoor unit is known as the condenser and serves a vital role in the HVAC’s proper function: it releases collected heat into the outdoor environment. 

If the condenser is excessively dirty, the system will struggle to disperse heat from indoors. As the AC unit struggles to function, it can begin to draw too much power, constantly tripping the circuit breaker and leading to a system that won’t turn on. 

Unfortunately, once the condenser becomes so dirty that it won’t turn on, a professional’s assistance is usually necessary. While most homeowners can handle routine cleaning to prevent this issue, professionals must remove severe dirt buildup carefully to avoid damaging the system. 

Note: If you’re unfamiliar with the system and clean it improperly, you could damage the compressor’s coil fins, which creates an entirely new problem. However, once a professional cleans the AC system and restores it to its former glory, you can prevent this issue from occurring later by cleaning the condenser routinely. 

10. Air Conditioner Drain Pan is Clogged

As your air conditioner works to cool your home, it also serves as a dehumidifier. If the system didn’t pull moisture from your home as it cooled the air, your skin would likely feel cool and clammy due to the high humidity level. So, the dehumidifying function is essential to a healthy HVAC unit. 

Since the AC system is collecting moisture, it has to send the water somewhere. So, where does it go? The system collects the excess moisture from your home in a condensate pan, which is conveniently tucked underneath the evaporator coils in the indoor unit. 

From the drain pan, the water flows into the condensate drain line, where it’s disposed of outside. If the drain pan or condensate line becomes clogged, it can lead to issues with the system turning on. Although the condensate pan sometimes features a second drain line to avoid problems, it too can become clogged. 

If both drains are full and can not escort moisture out of the pan, the system triggers the float switch, which abruptly turns the AC system off. The float switch functions as a safety mechanism, as an overflowing drain pan can lead to water damage in the unit and the surrounding area of your home. 

So, if your AC is not turning on despite your best efforts, check the drain pan. Use a wet/dry vacuum to remove excess moisture and debris from the drain pan. If you do not have a wet/dry vacuum, it might be easier to have an HVAC professional handle the cleanup for you. 

You can avoid this common AC problem in the future by regularly checking the drain pan and float switch for moisture buildup and clogs. 

11. AC Motor Failure

HVAC technician checking the motor

Unfortunately, AC units do not last forever. After a while, essential parts of the air conditioning system might begin to fail, leading to significant issues with the HVAC unit’s overall function. If the unit makes a grinding noise when it kicks on, this could point to the impending failure of the motor. 

Although motors in AC units are sealed to prevent issues that could arise from contact with outside air, debris, or water, this seal can wear out and come off after a while. When this happens, the oil trapped within the motor can seep out, causing the motor blades to begin malfunctioning. Eventually, once the system runs out of oil, the motor blades might stop working entirely. 

Once the motor fails, many homeowners choose to replace the entire unit. However, while this might be the best choice for some units, it might not be your best option. 

Note: Generally, replacing the whole AC system is better if replacing the motor costs more than half the original price. But if replacing the motor costs less than that, you might decide to replace the air conditioning motor instead of the entire system.

If your AC unit’s motor is faulty and still under warranty, the manufacturer should be able to replace it at no charge to you. Depending on the warranty terms, you may or may not have to pay for the new air conditioning installation.

Of course, you can do whatever works best for your unit and situation. Consult your HVAC specialist for assistance if you’re not sure of the best course of action for your central air system.

AC Not Turning On Still? Contact a Professional

If your air conditioner is still not turning on, despite your best efforts, it’s time to call an HVAC professional. After all, who wants to sit in a sweltering house with no escape from the summer’s heat? Not us– we need air conditioning.

So, do not hesitate to call a professional HVAC technician for help. Click the link below to find or get a quote from an HVAC contractor near you for quick air conditioning service and repair.

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Jonathon Jachura
Jonathon is a mechanical engineer with over ten years of experience in the HVAC industry. He has hands-on experience with all types of HVAC systems.

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