10 Reasons an AC or Thermostat Won’t Turn off

You expect a comfortable temperature inside your house on hot summer or cold winter nights. That is why you invest money in an air conditioner.

Generally, cooling systems of that type should last 15 to 20 years. Unfortunately, there is no guarantee of its long and unproblematic lifespan.

One of the common issues you can face is that your air conditioner won’t turn off. Normally, it should work for a short period till the room reaches a desirable temperature. It is not just about uncomfortable temperatures when it functions without stopping.

The greater concern is your electrical bill after that enthusiastic work. Luckily, there are ways to fix your air conditioning machine. Yet before coming to that, let’s see why it happens.

Table of Contents

10 Reasons an AC or Thermostat Won’t Turn off

It is more logical to think that when something breaks down, it will stop working. With air conditioners, it is not necessarily the case.

Sometimes it won’t turn off even when it reaches the set temperature. Ceaseless work is not only ineffective but energy-consuming.

There are a few explanations for that. Your AC might have the wrong thermostat or fan settings.

It can also be too dirty or have faulty units. To make a proper diagnosis and resolve an issue, check out ten reasons why an AC won’t turn off and how to fix it.

Often, the conditioning appliance is not the one that keeps working. The air conditioner fan tends to run incessantly as well. The main reason why it happens is the wrong thermostat settings. For proper operation, the thermostat should be set on AUTO mode.

1. The thermostat settings are wrong.


One of the simplest explanations for the ongoing air conditioner fan work is wrong settings. When you activate the ON setting on the fan’s thermostat, it does not stop working after the cooling cycle.

In fact, it does not stop working at all and turns the room into a refrigerator. To fix this, you just need to switch on the AUTO setting.

The other reason it can happen is the people you live with. Sometimes it isn’t easy to agree upon the same temperature. The functions of a thermostat can be seen in the table below.

Temperature settingAllows you to set the desired temperature
Temperature sensingMeasures the ambient temperature in the room
Fan controlControls the operation of the fan
Programmable scheduleAllows you to set a schedule for the thermostat

When someone changes settings all the time, the AC keeps running until the moment it reaches the required temperature. In that case, you need to resolve communication issues within your family.

2. The refrigerant leaks out.

A refrigerant is a chemical substance that operates in the cooling process. Because of it, the warm air turns colder inside the AC. The refrigerant might leak because of:

  • Corrosion
  • Vibration
  • Physical damage
  • Poor installation

When the refrigerant leaks through faulty coils or a broken expansion valve, the air conditioner fails to take in warm air. It will work harder to fulfill its task without much success.

If you suspect that a leak of refrigerant is a case of your AC malfunctioning, there is only one resolution you have. It is time for you to open your valet and call a technician.

They will use a special detector called ultraviolet dye to spot the leakage. If the results are disappointing, they will patch or replace the damaged part.

3. Air conditioner filters are clogged.

AC filter

Clogged air filters will eventually happen if you do not change them once in a while. Ideally, you should do it every 30–90 days.

The more you neglect your duty, the more dust and pollutants outside the AC unit will enter the filter. When it happens, the AC stops working efficiently and takes more time to cool. 

Remember that having pets or smokers inside of a house also affects how fast it will take for the conditioning machine to become clogged.

If you have a spacious home, that is also why you change filters more often. Do not forget about this necessity because otherwise, the whole system will shut down.

4. The weather is too hot 

Even if an air conditioner is made for hot days, extreme temperatures are still challenging for it to deal with. Heat waves during midday in the summer are common for a moderate climate.

Weather ConditionEffect on AC performance
High temperatureAC has to work harder to cool down the air
Low temperatureAC may not need to run as often
Rain and high humidityAC is at risk of water damage or mold growth

If you live in one of the hot countries, that means your air conditioner machine is a hard-working one. The thing you should do is pay attention to its behavior. If it works normally during cooler times of the day, there is no damage.

5. Wrong size air conditioner

Sure, it is cheaper to buy a small conditioner than give away lots of money for a large one. This economic hack is derived from bad ones. You should select your AC according to the size of your room.

The more square meters you have, the larger you need to be. When a conditioning appliance is too small, it starts working harder in order to cool down the space. 

If you are the person who always puts the economy in the first place, think about all the energy a small AC will consume to cool down a large area. The bill for that will shock you. The other downside of an unsuitable conditioner is that, eventually, it will break down.

If you want to save money, buying a Honeywell Portable Air Conditioner is better. It is intended for cooling small areas you are using. Honeywell is much cheaper than window air conditioners or central AC systems. It also consumes less energy than expensive ones.

6. The evaporator coils are clogged or frozen.

evaporator coil

The evaporator coil is essential in the cooling system. They absorb hot air from outside the AC unit and move it forward into the system.

The other function of evaporator coils is to keep refrigerant cool. When the fan sucks up the air, the refrigerant turns into vapor. In that state, it consumes the heat and travels to the compressor.

Several issues can happen with evaporator coils. They can get frozen or clogged. Dust and debris frequently become lodged within the coils. When it happens, the cooling cycles take more time than usual.

The other unfortunate outcome of clogged evaporator coils is that AC can discharge hot air into the room instead of making it colder.

If the air filter is dirty, there is insufficient heat inside the evaporator coils. On the contrary, there is too much moisture, which freezes out with time. With this one, you can easily kill two birds with one shot.

Turn off the AC and spray warm water with detergent on the coils. Then wait 10 minutes and wipe the dirt off the surface. That should bring evaporator coils to a productive life.

7. The fan works at a slow pace.

The reason why a fan can work slowly is dirt. Unclean blades tend to lose their usual speed. Despite any damage inside, your AC is still programmed to do a good job of cooling space.

Other causes that will make the fan work at a slower pace include:

  • Malfunctioning thermostat
  • Damaged fan blades
  • Low voltage
  • Faulty fan motor

When it detects a warmer temperature than needed, it works to lower it. However, a slow fan makes the task impossible to complete. As a result, the air conditioner runs for hours and hours with little success.

8. The thermostat is damaged.

Thermostats are used to measure indoor temperatures. It uses this information to turn on or off the cooling process. If the thermostat is faulty, the conditioner will keep working incessantly.

In a technical store, they say cooling appliances can last about 15-20 years. However, it is not guaranteed that some of its parts will not require replacement.

The thermostat is the component that should be replaced every ten years. Otherwise, it will start detecting incorrect temperatures.

9. A faulty relay switch

The part that operates the power supply in your conditioner machine is a relay switch. It provides the compressor and the clutch with electrical energy. If the relay switch is closed, it supplies the air conditioner with constant power.

A relay switch can stay in the closed position because of a damaged contractor. There are possible ways for you to fix it. However, the most efficient resolution to this issue is to have it replaced by a technician.

  1. The fan limit switch is jammed.

Correct fan settings do not ensure it will work properly in a cycle system. The problem is within the fan limit switch. When jammed, it distorts the connection between the thermostat and the fan.

Not only does the fan fail to follow instructions set on the thermostat, but it also constantly receives power. Then you notice that the fan blows on its own, disregarding the cycle regime.

Before asking for professional help to repair your air conditioner, you might want to try to fix it yourself. Here are some steps for you to go through that might be of some help:

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

  1. Correct the temperature on your thermostat.

    The right temperature is the key to good operation. If the temperature in your apartment is higher than the one set on the thermostat, AC will work incessantly.

    To avoid that, you can increase the set temperature a couple of degrees above to exceed the in-house one.

  2. Give your air conditioner a proper cleaning.

    As you noticed, the air conditioner is an appliance that likes cleanness. Even if it works with air, it is not a vacuum cleaner, so it is better not to treat it like one.

    Proper cleaning once in a while will only do AC well. Start by replacing the dirty filter. Give some proper attention to evaporator coils and outdoor condenser during cleaning.

    The other useful thing you should consider doing is putting away any obstacles that shut out access to air.

    The other thing you should clean as well as blower fan. When it is dirty, it fails to transmit cool air, and that leads to ceaseless work. Before starting the cleaning, make sure to cut off electrical power.

    Remove everything that stands between you and the fan blades. Those are the access panel and circuit board. Then carefully unscrew the blower motor and take it out.

    Clean the fan with a tiny brush and put everything back as it was when you are done.

  3. Turn the AUTO regime on your thermostat.

    If your fan is working within the ON regime on the thermostat, the air conditioner won’t stop.

    If your conditioner is not set to AUTO, the fan will continue blowing even if the whole unit is off. For that not to happen, make sure to set the correct thermostat regime.

  4. Choose the most suitable place for your AC.

    Where you locate your AC matters as much as what objects surround it. Especially if you have a window AC, it is better not to put it under the one that gets direct sunlight.

    The heat from the sun will make it harder to cool the space. Remember that surrounding it with plants is also not a good idea. The place where you put your conditioner should be spacious and free from excessive objects.

Maintenance guide

A long and malfunction-free lifespan is what every homeowner dreams about. However, do not expect to have it without making any effort.

Not putting your cooling system in for regular maintenance is not only an issue of money. However, you will pay more for repair or reinstallation if you don’t think good maintenance is necessary. 

The other fault is waiting in a long queue for repair when your AC breaks down in the hot season.

It may surprise you, but many people hardly do anything with their appliances unless they break down. To ensure you won’t be troubled with faulty AC in the future, keep in mind the following suggestions:

First of all, put your air conditioner on a regular inspection routine. Nearly all manufacturers suggest giving your AC to professional technicians who will validate its efficiency.

No doubt this will cost some money, but serious repairs usually cost a lot more. If there is any malfunction, the technician will find it at an early stage. Repairs of mild malfunctions cost less than those of the latest stages. That is a sign of good economic advice. 

Another thing that you should always keep in mind is that your AC needs to be lubricated every once in a while. Air conditioning consists of multiple moving parts that lose their mobility with time.

A cooling machine that has resistant motors consumes more electrical power. Not to mention, it wears out faster and needs more repairs. To anticipate that, do not forget to lubricate it.

Finally, always keep it clean. Change air filters once a month. You should clean the blowing compartment, evaporator coils, and condenser from dust and debris.

To remember these tips, save this short and simple table for future reference.

Maintenance Tips
Clean or replace air filters regularly
Keep the outdoor unit free of debris
Check and tighten electrical connections
Lubricate moving parts
Inspect and clean the drain line

The other useful suggestion is always to pay attention to the working pace of your AC. You won’t miss any malfunction, in case there is one. The sooner you diagnose it, the better.

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