16 Reasons Your AC Is Not Turning On & How to Fix Them

You rely on your air conditioner to perform reliably every time you turn it on—after all, it’s your go-to for comfort throughout the year. However, there are times when your HVAC unit might let you down and refuse to start. If you’re experiencing this issue, don’t worry!

It can be easily fixed as a DIY solution or, in some cases, with a phone call to a professional.

There can be various reasons for your AC to be acting up, from HVAC maintenance issues to your unit getting old. This blog compiles an extensive list to help you figure out why your AC is not turning on and how to troubleshoot the cause.

1. Thermostat Malfunctioning

Your air conditioner has stopped working all of a sudden. You panic and start calling different HVAC experts.

But stop for a second. Have you checked your thermostat?

Thermostat malfunctioning can have an impact on your air conditioner’s performance.

First, check if the display of your thermostat is lit. If it’s off, it cannot signal the AC to turn on. Second, check your thermostat’s batteries if you have a battery-operated thermostat. If the batteries are fine, then check the working of your thermostat. Set it to a cool setting, keeping it 5-6 degrees lower than the indoor temperature. After a few minutes, place your hands in front of the AC vane to feel the cold air. If it has turned on, then voila, you have solved the issue!

But if your AC still hasn’t turned on, turn off your thermostat and remove the cover to check its components. Look for debris or corrosion buildup. Also, look for blown fuses; sometimes, they are the culprit. You can clean out the debris with a soft brush, but you must contact a professional for corrosion issues.

Further, check if there are any loose screws or wires inside the thermostat. Again, you should refer to the user manual for correct wiring schematics.

2. Low Refrigerant Levels

One of the reasons your AC is not turning on could be due to a refrigerant shortage.

A refrigerant is a cooling fluid residing in an AC’s coils. It is mainly responsible for providing the much-desired cool air from your AC or hot air in the case of a heat pump.

The refrigerant shortage is due to something other than your air conditioner using up the fluid. Instead, leakage is a likely culprit in this situation. The cracks in the AC coil may build up over time, leading to refrigerant leakage. Further, not taking time for regular maintenance can lead to corrosion in the long run.

You cannot do much on your own in this situation as it is not just about filling the refrigerant; the levels must match exactly with the levels specified by your AC manufacturer. You would have to contact a professional to check the refrigerant levels and determine the reason for the leakage.

Avoid this problem in the future by ensuring regular maintenance of your air conditioner.

3. Clogged Air Filters

Do you remember the last time you cleaned your AC filters?

If your answer is no, then it’s a big problem as your AC may not work properly due to dirty, clogged filters. No matter what type of air conditioner you have, cleaning the filters is a must!

The filters ensure proper air circulation. If they are filled with debris, airflow is blocked. In this case, your system has to work harder to cool your home, and it can stop working overtime.

It is recommended that you use a smart thermostat for your central HVAC system or a smart mini-split thermostat to monitor your AC’s air filter cleanliness level. Continuous monitoring can help avoid clogged filters in the future.

4. Your AC Is Freezing Up

Dirty air filters, clogged drain systems, and faulty compressors can cause your AC to freeze up. Running the AC on a cold night or lack of adequate refrigerant can also cause this problem. This hinders your system’s functioning and, in some cases, is the reason why your AC unit is not turning on.

The indoor unit of your AC has the evaporator coil, and the outdoor unit contains the compressor. The refrigerant line is between these two components. When the airflow is restricted, warm air from your house does not reach the refrigerant, which then becomes so cold that any moisture on the coils freezes.

It’s scary, but you don’t need to panic. Shut down the unit immediately and let the ice thaw. Unfreezing will take some time, depending on the amount of ice. You can use a hair dryer to speed up the process. If you notice water dripping outside the drain pan, use a wet vacuum to clean it.

Once the AC has thawed, let it dry completely. Also, dig deeper into why your AC coils froze in the first place. Was it dirty filters or something else? Contact an HVAC technician and find out the exact cause.

5. Your AC’s Capacitor Has Died

If your HVAC unit has trouble starting, starts and stops abruptly, or makes unusual noises like a clicking sound when you turn on the outdoor AC unit, chances are that the AC’s capacitor has died down.

The capacitor is an integral part of your HVAC system. It is connected to the motor’s circuit and gives the motor an initial push to start running. The capacitor disconnects from the circuit once the motor reaches a specific speed.

There are two types of capacitors:

• The start capacitor provides voltage to get the motor started
• The run capacitor provides energy to keep them running

What Causes the Capacitor to Fail?

Your AC’s capacitor is sensitive to heat. Overheating can be caused by your AC working hard to achieve the desired temperature or by its exposure to the sun. For example, if your outside unit is installed on the roof, it will likely become a victim of overheating on hot summer days.

Avoid setting the highest or lowest temperature on your thermostat during extremely cold or hot days. This can also cause the unit to work harder, resulting in an overheated capacitor.

Power outages and power fluctuations can also significantly damage the capacitor. To prevent damage from power fluctuations, consider installing a surge protector.

Furthermore, old age can cause it to die down as the capacitor’s ability to release energy decreases over the years.

As far as age is concerned, regular maintenance will help you detect capacitor problems early. The solution is quite simple – have an electrician replace the capacitor.

Note: Never try to replace the capacitor yourself, as there is an electrical charge stored in it; there is a risk of severe electric shock. Never try to run your AC on a bad capacitor, as it can burn the motor attached to it, and replacing the motor can be quite costly.

6. Dormancy Issue

If you cannot figure out why your air conditioner unit is not turning on, check the fan. In case the AC fan is not working, it could point towards a dormancy issue. Provided that your cooling system was lying dormant in winter and you switched it on after some time, then the fans may find it hard to start rotating again because of the dirt buildup.

If your AC isn’t turning on after a period of dormancy, start by performing a pre-season check: clean the unit, inspect for any physical damage, and ensure all connections are secure. Run the system briefly to identify immediate issues and verify that the thermostat is set correctly and functioning properly.

7. AC Not Turning On? — Check the Switch

It’s the most obvious reason, but people overlook it all the time.

Like any other electric appliance, your AC has an ON/OFF switch. You will find it near to where your system is installed.

If you were doing some maintenance tasks or a technician came up to check on something, they may have turned it off. Flip it back, and you will be feeling the pleasant breeze in no time!

Whenever your system refuses to turn on, check the switch before you do anything else.

Also, try checking the indoor shutoff switch. The switch is usually in the attic, closet, or near the furnace. If it’s off, turn it back on, and your AC will start working as normal. It’s best to label this switch to prevent anyone from mistakenly turning it off.

8. Debris Laden Condenser

Is your external AC unit not turning on?

The external or outside unit of your AC is called a condenser. Its job is to release the heat collected by the inside unit to the external environment.

Without regular AC tune-ups, the condenser can get dirty over time. Dirt acts as an insulator, so it has to work harder to disperse the heat. The condenser will start drawing too much current, tripping the circuit breaker, and your AC won’t turn on.

If you think the solution would be easy since you can clean the condenser yourself, well, there is still time. Once it is non-functional due to dirt, it may be time for a professional clean-up. Improper cleaning can damage the compressor coil’s fins, which is way worse than the dirt on the coils.

It’s best to clean your outdoor unit as part of your spring HVAC maintenance to avoid any major issues in the hot summer months.

9. Tripped Circuit Breaker

If you have tripped the circuit breaker, your AC won’t turn on.

A circuit breaker is a safety tool that turns the power off in case of heavy voltage.  This may be caused by using high-voltage appliances or power surges in the electricity grid.

You need only find the air conditioner circuit breaker and turn it off completely. Then, wait for a few minutes before turning it on.

Safety tip: If your AC circuit breaker keeps tripping, do not try to turn it on. It indicates a high voltage that can cause an electric fire, and it needs to be fixed by an expert.

10. Your AC Requires Resetting

When your AC is having trouble turning on, a simple reset may be the solution. Check your AC manual and see if your unit has a reset button, as not all HVACs do.

• If your unit has it, hold the reset button for 2-5 seconds and then release
• If your system doesn’t have a button, you can manually reset it. Flip the circuit breaker that powers your AC. Also, turn off your AC switch. After 5 minutes, turn the breaker and AC switch back on.
• Another way to manually reset is to turn your thermostat off for 5-10 minutes and then turn it back on.

After performing the AC reset, set your thermostat to cool and at a low temperature. After some time, place your hands in front of the vents to confirm that your unit is doing its job.

11. Is Your AC Not Turning on or Has It Run Its Course?

Your AC has stopped running, and you are wondering why. If it has been your comfort companion for quite a long time, it may have reached the end of its lifespan.

But how can you actually tell if it’s time to say goodbye to your AC?

Following are some signs indicating why your AC is not turning on: 

• You notice a significant decrease in HVAC airflow. Also, your AC is blowing warm air in cool mode. The decreased airflow can be due to dirty filters, but if cleaning the filters does not work, your AC has aged and needs replacing. The
• Your AC requires repair services occasionally, which could indicate problems related to its lifespan.
• Your electricity bills are increasing at an abnormal rate. This is because, near the end of its life, the AC becomes sluggish and overworks to maintain the desired temperature. You can have an energy audit to see if this is causing the bills to increase.
• The inside unit of your AC is leaking It may be due to a refrigerant leak, but even if the issue does not get resolved, it’s time for the unit to go.
• If your AC is making weird, loud noises such as grinding, screeching, or rattling, it’s time to replace it, as this signals a serious problem.
• Your air conditioner smells bad. It could be due to molds growing inside your unit or due to dirty filters, but if the smell does not go away, consider replacing it.

Some of these indicators might just be dealt with with a professional tune-up, while others might require a replacement. Do not decide on your own; have a professional thoroughly check your unit before you go for a replacement.

Also, read these 8 ways to extend the average life of your AC.

12. Clogged Drain Pan

Your air conditioner unit not only cools or heats your house but also removes moisture from the air. So, where does that moisture go?

It is collected in the drain pan, located underneath the indoor unit evaporator coils, and then flows into the condensate drain line, which is directed outside.

With regular cleaning, especially in areas with high humidity, the drain pan can avoid becoming clogged. The pan has a secondary drain to prevent clogging. But if both are full, this triggers the float switch, which turns the AC off. It is a safety mechanism that prevents excessive leakage in your house and prevents damage to the unit. But even then, the water leak from the clogged pan can damage your walls, ceilings, and furnishings.

Your AC will turn on once the pan is cleaned and the float switch is turned down.

You can use a wet/dry vacuum to suction the blockage out, but doing it yourself will be really messy.

To avoid this episode, perform regular maintenance. You can use a wet/dry vacuum during routine cleaning.

13. Damaged Motor

If you hear a grinding noise when you turn on the AC, it is not a good sign as it may indicate malfunctioning motor blades.

Motors are sealed to prevent contact with the outside air, water, or debris. Over time, due to old age or lack of maintenance, the seal can come off, and the oil, which was sealed within the motor and needed for lubrication, seeps out. Without oil, the motor can wear out and stop working entirely after some time. The outside unit cannot dissipate heat if the motor is faulty.

One question that arises: should you repair the motor or replace your air conditioner?

Here’s a tip that will make it easy to decide: If it costs half the original price, consider replacing your system. Contact an HVAC specialist for a thorough inspection.

14. Faulty Power Cord or Outlet

Sometimes, the issue is not severe; it’s just that you are anticipating the worst. So, examine simple things that are right in front of you; check the power cord, for instance.

If your AC is stored for the season, the power cord can become frayed and wear down. Unplug the cord for proper examination. If it shows signs of damage, you will have to replace it.

Or maybe it is not the cord but the outlet that was plugged in. You can check if the outlet works fine by plugging in other appliances. If none of them work, you know what’s causing the issue.

Safety tip: Never attempt to repair the cord or power outlet yourself. You risk getting an electric shock if you don’t turn off the power supply. Just turning the switch off won’t do it; you have to turn the power off from the main power box.

15. Your AC Is Not the Right Size

Did you take into account the size of an air conditioner when buying it? Well, it is a mistake that is continuously overlooked but can greatly impact the HVAC performance.

An air conditioner that is not the right size will have to work harder and eventually break down completely.

When your AC is larger than required, it will keep turning on and off quickly, increasing wear and tear. Further, it won’t be able to remove the excess humidity as it won’t stay on for a sufficient time.

On the other hand, a small unit will have to run for a long time to cool/warm the house, which may cause the capacitor to overheat.

An HVAC system that is not the right size can also wreak havoc on your bills.

Unfortunately, the only solution is to replace the unit.

Some parameters determine what size you require, such as the area of your house, climate, number of windows, and insulation level. You will have to go for a professional evaluation to find out the perfect size of air conditioner for your home.

There is also an equation that roughly estimates the right size of AC. 

(Square footage of your home x 25/ 12000) – 0.5 = Required AC size

Let’s say your area is 1000 square feet.

(1000×25/12000) – 0.5= 1.5

You require a 1.5-ton AC.

16. False Temperature Readings

Your AC might only turn on if it’s receiving accurate temperature readings. This issue can arise from a faulty thermostat sensor or a sensor placed in a poor location, such as near windows, doors, or heat sources.

Ensure that your thermostat is centrally located, away from direct sunlight, drafts, and other heat sources. Also, verify that the temperature is set correctly. If the sensor’s location isn’t the problem, it may need recalibration or replacement. Regular thermostat maintenance, including cleaning and calibration, can prevent false readings and ensure accurate temperature control in your home.

In Conclusion

If you’ve successfully diagnosed and fixed why your AC wasn’t turning on, congratulations! However, you should still contact a professional for a thorough inspection to prevent similar AC issues in the future. Having an HVAC expert perform an annual inspection and keeping up with regular maintenance can help avoid potential AC problems down the line.