17 Reasons Your Air Conditioner Is Not Working (+Fix)

When summer approaches, we all want to get to a room with an air conditioning unit. But, here is the thing about these units. They do not always work properly, especially when you need them to work at their best. 

The air conditioner doesn’t work due to dead thermostat batteries, a blown-up fuse, dirty coils and filters, a faulty compressor, improper fan settings, low refrigerant, and condenser problems. To fix it, replace or repair the faulty parts and correct the settings in the thermostat and fans.

Since there are multiple reasons, you need to find the right one for your air conditioning unit. In this guide, we have shortlisted some major reasons behind an air conditioner not working and their solutions. Though you can solve some yourself, consulting HVAC experts is highly recommended while troubleshooting. 

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Why is my air conditioner not working properly? 

When we say that the air conditioner is not working properly, it could mean several things. 

For example, the unit is not cooling properly, not starting when it needs to work, not ending the cycle, etc.

There could be numerous reasons behind the problem, and you must diagnose the right one and confirm it before fixing it. 

Here is a list of the expected problems behind an air conditioner not working:

1. The thermostat batteries are dead

Sometimes, we panic so much that we forget to look at the simple things. 

A thermostat with a dead battery can make your air conditioner not work properly. 

The simple solution here is to change and replace the thermostat batteries. 

While buying the batteries, make sure that the batteries match the thermostat’s make and model. 

Otherwise, it won’t work, and the problem will stay unsolved. 

Also read: 12 Reasons Your Thermostat Is Blank+Fix

2. The indoor disconnect switch is off

The indoor disconnect box is the central nervous system of your air conditioning unit. 

The switch is located in the attic or the garage.

The air conditioner won’t work properly if the switch gets bumped accidentally and turned off. 

Before troubleshooting, you must confirm that the disconnect switch is turned to the ON position. 

3. The outdoor disconnect switch is off

This switch is installed next to the air conditioning unit. 

You or someone might have turned it off during lawn maintenance or other causes, for which the air conditioner may not work properly. 

You need to check the switch to confirm the problem and turn the switch back. 

4. A tripped circuit breaker or air conditioner

If the breaker connected to the air conditioner tripped, your unit would not start. 

To confirm it, check whether the breaker connected to the HVAC system has tripped. You only need to reset the breaker. 

Turn the breaker to the off position, wait for a few seconds, and then turn it on again. 

Breakers often trip due to overloading. 

If the breaker trips again after resetting, do not reset it again. 

Instead, call for an HVAC expert to look into the matter. 

Can I reset my air conditioner?

Most times, the professionally installed air conditioners do not have reset buttons. 

Sudden power outages or surges are one of the common reasons behind an air conditioner not working properly. 

However, the problem resolves if the power remains again for a very long time.

However, checking the system after a power outage and breaker box is good. 

The power outage could sometimes be due to a tripped breaker

One obvious indicator is a blank thermostat.

Turn the air conditioner off at the thermostat and reset your circuit breaker. 

Please wait for 30 minutes before turning it back on. 

If you still face difficulties making your air conditioner work, call a professional before the problem worsens. 

5. Blown-up fuse

A blown-up fuse between the thermostat and the air conditioner means a bad battery. 

The unit cannot work properly to give you the desired temperature if you have a blown-up fuse in your air conditioner. 

First, you need to confirm the problem. 

Turn off the air conditioner at the breaker and pull out the fuse for a continuity test with a multimeter. 

If there is no voltage, the fuse has probably blown up. 

You need to replace the fuse with a new one with the help of an expert. 

While buying the fuse, consider buying the model that suits your unit. 

6. Blown-up transformer

The deal is the same as the blown-up fuse. 

Your air conditioner will not work unless you replace the transformer. 

Sometimes a bad contactor will also result in the same problems. 

It is generally the contactor that leads to a blown-up transformer. 

The contactor’s contacts get stuck with each other. 

So, you will have to fix the contactor too. 

Sometimes, a slight tapping helps to release the contacts. 

At other times, you need an HVAC expert’s help. 

7. Starting parts on a fritz

The air conditioners depend on two capacitors inside the outdoor unit. 

One capacitor is the start capacitor, and another is the run capacitor. 

The capacitors look like giant batteries. 

The capacitors hold the power of the air conditioner to turn it on and keep it running. 

But if the capacitors are dead or have ended their lifespan, the air conditioner will not work properly. 

Since they eventually fail, you need to hire an HVAC expert to replace the capacitors. 

8. Dirty indoor and outdoor coils 

An air conditioner will have two coils – one for the outdoor unit and another for the indoor unit. 

These coils will get dirty over time if you do not maintain the unit regularly. 

In that case, the air from the air conditioner will not be cold despite setting the thermostat to ‘cool.’ 

Due to the accumulation of dirt and debris, the system cannot remove the heat from your house, which means the unit won’t work well.

So, you must ensure regular cleaning of the coils to avoid the problem.

9. Dirty air filters

The air conditioner not working could be due to the dirty air filters inside the unit. 

Over time, the filter accumulates dirt, debris, and other air particles from the environment. 

As a result, the air cannot flow through the filter due to the blockage, affecting the unit’s cooling potential. 

Based on the filter condition, you can either change it or replace it. 

Pull out the cover plate, remove the filter, and replace it with a new one. 

Sometimes, the filters are washable and reusable. 

You can wash the filter, dry it, and put it back in place.

10. High atmospheric temperatures

Every air conditioner has a specific operating temperature for which the unit works efficiently. 

Suppose the surrounding temperature is so high that it crosses the limit of the optimum temperature. 

In that case, the efficiency of the air conditioner will reduce.

During the summers, sometimes the temperature reaches so high that it becomes very difficult for the air conditioner to reach the desired temperature and cool down your room. 

During such a condition, you might feel like the unit is not working properly. 

But that is not always the case. 

The unit works hard to reach the goal, but the surrounding temperature becomes excessive to handle.

11. Faulty compressor

A compressor is a motor that compresses the coolant to circulate it through the evaporator coil. 

If the air conditioner is not cooling, the compressor is defective, and the AC cycle gets broken.

The problem requires immediate fixation because the compressor can be expensive and an important part of your unit.

You may not be able to fix it yourself. Consider hiring a professional to deal with it.

12. The fan setting is wrong

Some users are unaware of the air conditioner’s fan settings. 

There is more than one setting. 

The AC fans have three fan settings – low, medium, and high- like the ceiling and table fans. 

If the fan speed is optimized incorrectly, the unit will not work properly. Therefore, it will create an uncomfortable environment. 

If the fan speed is high, the unit will become overactive, and the energy bills will increase. 

On the contrary, low fan speed will not absorb the humidity and give you enough cool air. 

So, the best is medium.

13. Failed condensate pump

Checking for the condensate pump is easy. 

The pump has a low lifespan because it runs both the air conditioners and the furnaces. 

The pump has a test button. 

To check the condensate pump’s condition, ensure the basin has some water, and then press the test button to see if the pump is pumping the water out.

The condensate pump can sometimes trip the unit, for which the unit will not run, and create a pool where your unit is installed.

You will see a float on the top of the pump that will be stuck and shut off the pump. 

If the float got stuck, a gentle tap should correct the problem. 

But, if it is cracked, you need an HVAC expert to replace it and make your unit work again.

14. Incorrect air conditioner size

An incorrect AC size can be the reason behind the unit not working properly. 

Different square footage will need different sizes of air conditioners, and selecting the right one is difficult. 

Getting an incorrect air conditioner size will not let your unit work properly. 

If you get a very small unit, it will work harder to give you the desired temperature but won’t be able to give you. 

It will make you think that your unit is not working properly. 

Since the unit will struggle to give you the needed temperature without stopping the cycle, it will increase the energy bills. 

If the unit is too big for your house, it will require power and struggle to stay on. 

A big air conditioner won’t allow the machine to work efficiently. 

It will constantly turn on and off and create hot spots in your room.

15. Low refrigerant 

Sometimes, you think your air conditioner is not working because it cannot give your room enough cool air. 

It is probably because of the low refrigerant. 

The refrigerant fluid eliminates the heat and spreads cool air throughout your house. 

The AC unit will not meet your expectations if the level is low. 

It could be because the fluid is leaking due to rust, erosion, or cracks. 

You need to call a professional to replace the refrigerant tank and fill up the fluid.

16. Careless outdoor landscaping

If plants and shrubs are outside near your air conditioner’s condenser unit, they obstruct the airflow and cover the unit with dirt and leaves. 

It can overburden the condenser unit and make the system fail, resulting in insufficient cooling. 

As a result, the house owner thinks the unit is not working properly.

Make sure to have a 2 to 3 feet distance between the condenser unit and the trees and shrubs. 

17. Someone damaged the HVAC components.

Sometimes, you can accidentally bust the components of the HVAC system. 

So, something happened with your unit. For example:

  • The landscaper accidentally busted the refrigerant line. 
  • You pulled a wire by mistake while working on some unrelated project.
  • Kids threw a heavy ball or something to the outdoor unit and damaged something. 

Anything can make your air conditioner not work properly.

If you suspect any of these but cannot come to one point, call your local HVAC expert to help you.

Final thoughts

So, these are some of the common and major reasons behind an air conditioner not working properly. 

Since so many reasons exist, you must hire a professional before fixing anything. 

They can help you diagnose the main problem and fix it. 

You can prevent this by having routine maintenance of your unit. 

Consider checking it up whenever your air conditioner slows down or something you feel is incorrect. 

The best solution to all these problems is to call your local HVAC team for regular maintenance. 

The team will check your unit, detect if there is any problem or if any part requires replacement or clean up, and do as required. 

In that way, you can prevent maximum unit issues.

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Arthur Smith

Howdy! I am Arthur Smith, an electrical engineer who is extremely passionate about electronics. I have lived in different parts of the US and currently reside in Wisconsin. I am one of those rare children who knew what he wanted to study and do in life right from the start. I was a curious child who wanted to know how switches work and how the AC works, and I would always observe my dad whenever he would handle the wires and fix things around the house. I currently work as an electrical engineer at a reputed company and write for this blog. And I read loads of books or play video games in my free time.

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