6 Reasons an AC or Thermostat Won’t Turn off

With the world burning up by a few degrees yearly, we’ve become highly reliant on ACs and coolers. The summer is no longer a season we all once looked forward to.


The most common reason an AC or thermostat won’t turn off is damaged wiring. The way to fix an AC or thermostat that won’t turn off is to check and replace damaged wiring and ensure nothing else is causing the issue.

In this article, we also take a look at the following:

  • When the thermostat needs replacing
  • Extreme weather conditions

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Pool parties and trips to the beach are temporary ways of cooling down. But when you need a more permanent fix, you run to your room and blast the AC to the minimum temperature.

When the heat becomes unbearable, you’d like to have the AC on for hours. But eventually, there comes the point where the cold starts bothering you. After all, beating the heat was the only purpose. So what happens when your room turns into a winter wonderland, and the chill starts settling in your bones?

Naturally, you rush to switch off the AC, or your thermostat regulates the temperature for you. But the trouble begins if your device refuses to comply. Besides the additional electricity cost, multiple health risks are associated with staying in the AC for too long. 

So before you incur a hefty charge on your electricity or the hospital bill, we’ve gathered a few reasons why your AC is acting this way. Keep reading, and we’ll also help you fix the issue. 

Table of Contents

Reasons an AC or Thermostat Won’t Turn off

Here are the reasons an AC or thermostat won’t turn off.

Honeywell thermostat

Understanding the intricacies of home appliances might seem like a tedious task. But that doesn’t mean you should call for professional help right away or apply to an undergraduate program in engineering. Instead, you can look at your air conditioner and quickly determine the core problem.   

Here are 6 reasons why your AC or thermostat won’t turn off:

Damaged thermostat wiring

Your thermostat regulates the temperature according to the changes in the room temperature. If the sensor detects the room temperature to be too high, it lowers the temperature.

Several wires and connections are set in place for the thermostat to work efficiently. If any of these connections are loose, corroded, or worn out, your thermostat will not work. 

An easy way to identify which connection is faulty is by checking the color of the wire. Standard colors are used for each link, so it’s easier to detect the problem. 

For example, the red wire is known as 24-volt hot. It helps transfer the thermostat’s message to the AC.

Any fault with the red wire is likely to result in an issue of communication between the two systems. In contrast, the white wire is the heating connection. Whereas yellow is for cooling and blue is a common wire. 

You get a general idea about which system is likely malfunctioning by looking at the conditions of each wire.        

AC or thermostat needs replacement.

digital thermostat

When you invest in a home appliance, you hope to get the most out of the product. But even when you purchase the most high-quality and exclusive item, it will eventually stop functioning.

Typically, air conditioners have a life of about 15 to 20 years. But if proper care is given, you can drag their use to way above their expected life.

Your thermostat needs to be replaced if:

  • It is damaged
  • It is outdated and features old technology
  • It is malfunctioning and fails to respond to your commands
  • It is no longer accurate in controlling the temperature

If you’re an older model, you’re more likely to run into malfunctioning issues. Additionally, increased usage of the AC speeds up the aging process. For a hot climate area, it’s seldom that an AC crosses the 15-year mark.

Instead of removing the entire unit, it’s possible only your thermostat needs replacement. But if the thermostat gives faulty readings or does not respond to temperature changes, you’ll have to get it replaced. At best, a thermostat can only work for about ten years. 

Either way, you should get it checked one last time before you call it quits.      

Extreme weather conditions

older air conditioner

You may wonder why your AC suddenly stops working when the outside temperature increases to 100°F. The simple answer is that it isn’t designed to handle such a high temperature. Similar to how you struggle to keep it all together during summers, your AC is doing the same.

Check the table below to see the top 5 hottest states in the US. In these places, your AC will consume more power.

StateAverage temperature
Florida81° F
Arizona77° F
Texas75° F
Nevada72° F
California68° F

When the temperature outside is in triple digits, your AC has to consume more power to generate the same result. Due to the higher electricity consumption, some of its units may get fried up. As a result, malfunction is bound to occur. The victim could be the thermostat or another component.

One way to confirm your suspicion is by looking at the AC activity during different times of the day. If you find it working fine during the coolest parts of the day but breaking down once it gets too hot, the climate is at fault. 

For hotter climate areas, AC breakdowns and malfunctions are more common. The only solution is regular repairs and maintenance checks. Also, it might help if you limit your usage altogether. 

Congested air filters

It might seem that all problems related to a home appliance are always too technical. But that’s not necessarily the case. Sometimes, it’s merely an issue of negligence. With use, the air filters begin gathering dirt. And if not taken care of, it can get clogged up. 

Congested air filters make it difficult for the air conditioner to dispatch cool air throughout your home.

It has to work harder to keep the desired temperature. Whether it’s maintaining a low temperature or regulating the cooling with the outside temperature, essential AC functions are affected. 

The additional work an AC unit puts in requires extra power. And as you know, with great power comes great responsibility. Not only will your electricity bill spike, but there’s a significant risk of damage to essential components.

But if you’ve confirmed the issue lies with your air filters, there’s a simple fix. All you need to do is remove the air filters, scrape the dust away, run it under warm water and install it right back.   

It isn’t the correct size.

air conditioner

When purchasing an air conditioner, you might only consider the:

  • power consumption
  • cooling speed
  • and price.

But there’s another critical factor that many people tend to overlook. The air conditioner’s cooling capacity determines whether it’s the right fit for your room. 

The machine must work harder to reach the desired temperature if the AC is too small. As a result, each cycle is dragged longer.

The unit seldom shuts down. Typically, a cycle lasts about 30 minutes. So after a room has been cooled, the AC takes a break. With smaller units, the appliance runs on an endless cooling loop.

Before you purchase a new AC, make sure to follow these tips:

  • Measure the area you would like to cover
  • Determine how many BTUs you need
  • Decide what type of AC you need

We recommend figuring out the suitable BTU capacity for your room before you set foot in an appliance store. There are multiple online calculators which deliver near-perfect results. All you need to do is insert the room’s:

  • height
  • area
  • sun exposure
  • and climatic zone.  

Filthy evaporator coils

Repair and maintenance are essential parts of owning an electric appliance. Scheduling a regular professional visit helps keep your machinery in top condition. If you wait for the machine to break down, the repair cost will be unreasonably high.   

However, it would be best if you didn’t wait for a yearly visit to identify red flags. You must be extra cautious if the concern is about the evaporator coil.

The vital component aids the temperature regulation process by absorbing the heat of the air that enters the system. In return, the liquid refrigerant further cools down the air and releases it into the room.

A clogged evaporator coil results in longer cooling cycles and frost development. With little to no rest between different cycles, the air conditioner overworks and malfunctions differently.

If you’ve understood the coil placement, you can remove the debris by spraying a mixture of detergent and warm water. But if you don’t feel confident about your chiller knowledge, it’s better to call in the professionals.       

The air conditioner keeps running constantly & won’t turn off when the set temp is reached.

Air conditioner technology has vastly improved over the last few years. As a result, you’re no longer required to play an active role in regulating the room temperature.

Instead, all you need to do is set the thermostat to the desired temperature. Once the room temperature reaches the set value, the AC turns off automatically. 

All ACs have an automated regulation system. So if your unit fails to turn off even after the desired temperature is reached, there’s a more significant issue.

When the air conditioning unit runs continuously for a long time, excessive cooling builds up in the room. But that’s not all. You’ll notice:

  • water dripping from the AC vent
  • continuous mechanical noise
  • and fans icing up. 

There are several reasons your air conditioner refuses to comply. However, clogged air filters and greasy electric coils are at the top of the list. But if any such problem has persisted for a long time, it’s possible that things went wrong at installation. So either your AC is the wrong size for your room or fixed at the wrong place.

You might also want to take a look at the thermostat. Any faulty readings, damaged wires, or glitches could suggest a replacement or repair.

And if nothing else makes sense, it’s wise to calculate how many good years the chiller has left to give. A typical air conditioner works efficiently for about ten years. So if your unit has crossed its useful life, it’s probably coming to an inevitable end.       

The air conditioner fan keeps running when turned off.

Haier air conditioner

Machines are designed to work with near-perfect accuracy. Therefore, any changes in the regular patterns are a cause of concern.

The issue might be as simple as hearing a revving sound every time the AC starts up or as severe as your unit catching on fire. So before something serious occurs, we advise you to pay attention to small changes in detail. 

Maybe you’ve noticed the fan continuously running even after a typical 30-minute cooling cycle has ended. You’ll need to put on your detective hat. 

First of all, take a look at the fan setting on the thermostat. It should read ‘auto’ instead of ‘on.’ If it states the latter, the fan is programmed to work indefinitely until it’s manually switched off.  

Secondly, determine if the installed unit is the right size for your room. For example, a smaller AC will keep the fan and blower running to keep up with the thermostat’s requirements. 

Lastly, take a look at the thermostat if all else seems fine. A sensor replacement might occur if the thermostat readings appear faulty or inaccurate. In addition, any damage to the wiring will also likely result in a broken thermostat.    

Running into air conditioner problems in the summer is the last thing you want. Most professional technicians tend to be overbooked, and it may take days before you can score an appointment.

But before you call a technician, you can take a few troubleshooting steps to fix your unit. Here’s everything you need to follow:

How to fix an air conditioner that won’t turn off

  1. Change the temperature settings 

    The thermostat regulates the room temperature by cooling until the set temperature is reached. The AC will keep running if a temperature lower than the current room temperature is set. Therefore, you must set the thermostat at room temperature or a few degrees higher to see if that stops the unit from cooling. Hunter thermostat

  2. Adjust the thermostat fan settings

    Once the set temperature is reached, the fan eventually shuts down. Maybe you feel the fan is running even after the thermostat temperature matches the room temperature. Look at the fan setting and change it from ‘on’ to ‘auto.’ This shift in setting ensures the fan automatically stops working at the set temperature. 

  3. Improve the airflow

    Clogged air pathway results in the unit working harder and consuming more power, which may damage essential components. To ensure the system doesn’t have to work twice as hard, remove the air filters. Clean them with warm water and detergent solution. Keep scrubbing the filters until all dirt and debris have been removed.    

  4. Dust off greasy coils and blower fan

    With usage, the AC’s cooling capacity naturally reduces. But a more significant portion of its ineffectiveness is credited to the congested electric coil and blower fan. These components gather dirt over time which may affect the thermostat function. 

    Carefully remove the parts from the unit and vacuum the dirt from the fan blades and the coil. Once the loose dust has been cleaned, use a sponge or brush to scrub the parts with warm water and a detergent mixture. Later, allow the fan and the coil to dry off before returning them to their assigned places. Keep in mind to make this a monthly ritual.   

  5. Schedule an appointment with a professional.

    Sometimes despite your best efforts, the problem remains undetected. If your AC presents the same issue even after you’ve followed the above steps, you should look into seeking help from a professional. As a last resort, book an appointment with a technician. 

Importance of air conditioner maintenance

All electrical appliances have a set number of years before they’re sold at scrap value. But that doesn’t mean you can treat it however you want, and it will only retire at the end of its life. In contrast, maintaining your unit ensures various benefits. It includes:

Lower electricity bill

Regular upkeep means your AC doesn’t have to work harder to perform the same. When the air conditioner runs for the same time to reach a set temperature, it doesn’t use any additional power. Therefore, no extra consumption cost is added to your bill. 

If your electricity bill is too high, the AC might be responsible for this increase. Check out the table below to find out 4 reasons related to this problem.

Reason #1Your AC is old
Reason #2You are not performing regular maintenance
Reason #3The AC is always on
Reason #4 Your windows are not sealed properly

Enhance the life of your AC

As each year passes without regular maintenance, your AC only retains 95% of its efficiency. The lost 5% might not seem significant, but it hugely impacts your electricity bill and system efficiency. On the other hand, your AC retains most of its reselling value and performance if you schedule routine repairs.  

Higher efficiency

What a system expels largely depends on how efficient its functions are. With regular maintenance, the faults and malfunctions are recognized early on. Instead of the problems piling up and bringing the entire system down, you can eliminate them before the cells become cancerous. This way, you ensure the unit works with maximum efficiency.

No high repair costs

The cost and risk are significantly lower if a problem is identified in earlier stages. This is because a technician can resolve any minor inconveniences with regular repairs before they spread out. But if you leave your system untreated for too long, replacement and overhauling costs will prove a more significant burden.  

Tips on general AC maintenance

To make sure you get the best value for money, here are a few ways you can ensure your AC stays in top condition:

Unclog the AC drains

Since most components of an AC unit are connected, the air will carry dirt or debris settling in the drains forward to the furnace and other parts. So before you come across a severe problem, it is advisable to unclog your drains. Remove any dirt or algae that has settled in the space.

Change your filters.

Your AC filter is an essential part of the unit. It prevents any dirt or debris from being released into the room. Therefore, you must keep a close check on the filters. Typically, experts suggest a replacement every 30 days.

Keep the outside AC unit free from dirt.

Leaving a machine to rot will drastically reduce its useful life and increase the risk of malfunction. Therefore, you must ensure the entire unit is free from debris or dust. You can clean the area around the outside AC unit using a slightly damp cloth. And make sure there are no overgrown plants or David’s blocking the air passage into the unit. 

Conduct regular tests on your thermostat

Since most of the temperature-related issues are related to a thermostat, keep a close eye on this component. Conduct a random test by setting the desired temperature above the room temperature to see if the thermostat switches off the AC automatically.


Should an AC fan run all the time?

An AC fan isn’t programmed to run at all times. Instead, it is only supposed to function for the duration of a cycle. So if your fan continues to run even after a typical cycle of 30 minutes has ended, it’s likely that the fan setting is not set to Auto.

How long should AC run after reaching the set temperature?

Under normal weather conditions, an AC completes a cycle in 20 minutes. Further, it takes the unit up to 10 minutes to cool down. On hotter days, the duration of this cycle and the cooling-off period may increase by a few minutes. However, it only becomes a cause of concern if the cooling-off period lasts 30 minutes or more. 

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