What to do when your AC won’t turn off

Written by Adam Morris
7 Min read
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Table of contents

There can be so many knock-on annoyances that happen as a result of your AC not shutting off. In the summer heat, we all like to flip on the air con and feel those cooling airwaves envelop us.

However, if your system is constantly running but not completing the crucial work of cooling the room, then you’re going to stay warm, get annoyed by the running sound, and be hit in the pocket by increased utility bills. It’s a triple threat of annoyances.

So, what can you do if your air conditioner unit won’t turn off? Well, we can answer that but, first, we need to look at some of the reasons why your machine may be constantly cycling.

10 reasons why your AC won’t turn off

  1. Incorrect fan or thermostat settings
  2. Electrical problem
  3. Faulty thermostat
  4. Faulty fan limit switch
  5. Stuck compressor contractor
  6. Dirty condenser coils
  7. Dirty air filters
  8. Low coolant levels
  9. Incorrect AC size
  10. Hot outdoor temperatures

Incorrect fan or thermostat settings

Before you go taking apart your system or calling in any expensive repair firms, it’s always worth checking the small stuff. Take a look at your unit’s thermostat and turn up the temperature by a couple of degrees, this should tell your system that the correct temp has been hit and it can power down.

Additionally, you will also want to make sure you have your fan set to AUTO rather than ON. A lot of the time, that noise you can hear from the machine is the fan rather than the system running. Setting the system to AUTO will ensure the fan only runs when the system is going through a cycle.

Electrical problems

As with any electrical appliance your HVAC can run into some technical issues. For example, the relay switch component can sometimes become stuck which means the electrical circuit will remain closed and continue to power the AC unit. This can cause some pretty hefty utility bills that you haven’t even been getting the use out of.

Faulty thermostat

Before you condemn it as faulty, you may want to try changing the batteries in your thermostat. But if that doesn’t work then you may have to start thinking about updating your system. Most thermostats have an average lifespan of around 10 years. Just like another other appliance, over time dirt and dust from your home can get caught up in the inner workings of your thermostat and wreak havoc with the wiring.

Faulty fan limit switch

Much the same as the issue we covered off in the point about electrical problems in your system. Your fan limit switch may cause your fan to continue running even outside of a cycle if it’s stuck in the override position.

This will also mean that your system doesn’t look to be listening to your thermostat or controls. So you may have the right setting selected, but a faulty limit switch will mean the fan runs anyway.

Stuck compressor contractor

The compressor on your system is the big box that sits outside your property. The contractor controls the flow of electricity to the compressor. When the contractor is closed electricity will flow to the unit. Turning your system down enables this circuit reaction to take place.

Over time the contacts on your contractor can get hot and start sticking together. When this happens, the system is no longer able to disconnect so your compressor can’t follow the instructions set by the thermostat and continues to run.

Dirty condenser coils

Much the same as when your refrigerator is making strange noises, the condition of your condenser coils could be the culprit. Generally speaking, the condenser coils on your fridge perform the same job in your AC unit, they release hot air from the appliance.

The coils are full of coolant and they release the hot air from your room outside via the exterior unit. Your machine’s compressor then pushes air over the cool coils and into your room replacing that hot air with nice chilled stuff.

But to complete this task efficiently, they need to be kept clear of dirt and debris. When your coils are covered, the warm air can no longer escape therefore your room can’t cool down. To avoid your coils covering over, it’s best to stay up to date with your machine’s maintenance. But more on that in a moment.

Dirty air filters

However, it’s not just your condenser coils that can be adversely affected by collecting dust and dirt. As you can imagine if you live in a warm climate, the Sunshine Belt, for example, your air con will be running more regularly than most. But with more work comes more dirt.  

Cleaning your air conditioner filters is a relatively simple process, it’s just a case of removing the filter and getting rid of any dust, lint, hair, or other bits than can clog up the filter.

Low coolant levels

This may sound like a simple job of topping up your levels. But, the problem is, if you’re losing coolant then you may have a leak somewhere in your system. Damaged coils, cracked refrigerant lines, or a faulty expansion valve may be to blame. However, it’s best to get an HVAC professional involved to help you fix this one.

Incorrect AC size

Not getting the right sized AC for your home can become an expensive issue. Aside from being a costly outlay initially, an incorrectly sized machine will not work efficiently in your space.

When your machine can’t cool your space or something is causing it to work harder, this can cause it to short-cycle. Generally speaking, air conditioner cycles run for around 20-30 minutes depending on several factors including what temperature you set the thermostat to. If your machine can’t reach that temperature because it’s too small or too large, it will keep running on shorter cycles.

A short cycle is bad for your machine as it means it’s working harder than it needs to. But it can also mean that your energy bills start to creep up as you have an AC that doesn’t turn off.

Hot outdoor temperatures

We know, at this point you’re probably thinking: “what’s the point of an AC if warm weather causes it to not work properly?”. Well, that’s a valid point, but we’re not just talking about your average 70°F days.

Normally your system will be well capable of keeping you cool in most warm spells. But if you start to experience extended periods of hotter than usual weather (we’re talking upwards of 110° - 120°) then your machine will find it difficult to cool the room to the desired level. 

Let’s not forget that, although the air conditioner is great, it’s only capable of reducing the air temperature of a room by 20°. So if it’s 120 out, then don’t expect to be needing your woolly hat and coat inside. 

So, with all those points covered, how do you ensure your machine runs at peak performance for longer?

How to keep your air-con running smoothly

At Appliances Made Simple, we find that with most machines, their smooth operation can depend on several things. But one crucial element is care. Staying up to date with your machine’s maintenance and cleaning is imperative.

You can probably see that a good percentage of the issues outlined above have something to do with care and regular cleaning.

However, for other problems like issues with the electrics, coolant, or system sizing, it’s always best to speak to a professional about getting a fix in place. HVAC contractors will be able to calculate whether you have the correct machine for the job and, if not, they will certainly be able to recommend an alternative.

So, what happens if the problems persist?

Do you need a new AC?

Sadly, if you’ve tried all the above, your machine is now sparkling clean but still not shutting off, then it’s probably time to think about replacing your system.

Of course, there are a lot of variables that can affect the lifespan of your system. From weather conditions to regularity of use and care. But, generally, most professionals will advise you to think about replacing your air conditioner every 10 years.

Plus, from a maintenance perspective, it can get harder and harder to repair and upkeep machines where parts have become obsolete.

While we started this thing talking about how costly ACs can be, it’s more expensive, in the long run, to buy a new machine than to stand by a malfunctioning one for years.


When your air conditioner won’t shut off it can be an annoying issue. But, hopefully, with the above solutions, you shouldn’t need to put up with the warm air for too long.

Try the above fixes and stay up to date with your cleaning schedule and you should have a happy, healthy relationship with your cooler for years. Alternatively, though, don’t feel obliged to stick by an aged machine, they can cost you more than you think.

How do I know if my AC thermostat is bad?

There are several ways that your thermostat can tell you it's not working properly. It may just not turn on or your furnace or air conditioner may not be getting your room to the correct temperature. Try checking the batteries or remove the thermostat and take a look to see if any wiring looks loose. Also clean out any dust and debris in there.

Is it OK for my AC to run all day?

You should not be running your AC all day. If your air conditioner is not turning off then you should try checking the areas outlined in this piece. Your unit should cycle 2-3 times every hour to manage the temperature in your room, any more than this and it will short-cycle or over work.

Appliances made simple. 

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