Air Conditioner Keeps Running When Turned Off (What to Do)

February 23, 2024

Do you hate waking up to find your air conditioner running even though you turned it off last night? Or do you just not understand why it keeps running?

In most cases, the problem is in the wiring or the electrical components of the control board which would require help from an HVAC technician. In other cases, a dirty blower fan is to blame. This is an easy fix you should try before calling a professional.

In this article, I’ll explain how the air conditioning system works, and I'll go over possible reasons your AC keeps running when you turn it off, and what you need to do to fix it. I'll also go over some things you can do to keep your air conditioner properly maintained.

Reasons the Air Conditioner Keeps Running When I Turn It Off

All the components of your air conditioner work together to cool the air in your house. If one part of the system is not working properly, the rest of the process could fail causing your air conditioner to do unusual things like keep running when you turn it off.

Go through the list of some common problems with AC units below to try and find the root of the problem and determine if it is something that has an easy fix, or if it's something you are better off hiring a professional to help with.

Problem with its PCB assembly

The PCB, which stands for printed circuit board and is also known as the electronic control board, is often referred to as the brain of your air conditioner. It is is a circuit board where the logic operations happen. This is what controls everything like fans, compressors, pumps etc.

A faulty PCB assembly can cause the fan and compressor to run constantly, regardless of whether the temperature reaches the desired level.

You can use a multimeter to check the voltage, continuity, and resistance of your PCB to determine if it is working properly.

Problems with the thermostat

Thermostats are small devices responsible for taking note of your room's temperature and passing it on to the electronic control board. It works by measuring the temperature in different parts of your house and adjusting the heating or cooling system accordingly.

There are two main types of thermostat controls: relay switches and digital switches. You'll find both kinds in every modern HVAC system.

If you have a stuck relay switch, however, it could be the reason your air conditioner doesn't shut off when you turn it off. Basically, the dials in the relay switch thermostats usually line up to close the circuit to the air conditioner's components and communicates when to turn on and off the compressor. If the dial is not working properly, the compressor won't get the memo to shut off, and it will continue to run even when the temperature has reached its ideal setting.

Newer smart thermostats have a "test" button that you can use to check if your thermostat is working. If you have a standard model, you can use a multimeter to checking the wiring connections and determine if your thermostat is working. Make sure all the terminals are connected correctly.

Problems with the temperature sensor

The thermistor, also known as the temperature sensor, works a lot like the thermostat. It also measures the temperature and tells the compressor when to turn on or off. So a broken or faulty thermistor could be the reason why your AC keeps running when switched off.

To check if the thermistor is functioning properly, power down your AC by flipping the circuit breaker in your breaker box to the "off" position. Then remove the cover on your AC unit. Find the sensor and and check if it is in the correct position, or if it has been moved or bent away from the coils. If it has, return it to it's proper position. If that doesn't work, your thermistor might be broken and you would need the help of a professional to replace it.

It’s too hot outside

If your area is experiencing hot weather, there’s no doubt your AC might start acting up. When you set your thermostat to a certain temperature, the AC will work on getting the temperature in your house cooled down to that set temperature. Once it has reached that temperature, it will turn off.

But if your blinds are open and the sun is shining through the windows into your house, the thermostat will once again detect a higher temperature in your house thus, turning the AC back on.

This is an endless cycle on those hot summer days. Try to keep your curtains and blinds shut on days you are expecting hirer outside temperatures to keep it cool inside and save your AC from working overtime.

Short-circuiting

Short-Circuit happens due to faulty wiring in the system. When it does, the blowers don't get the memo from the thermostat causing them to go haywire. So, when you turn your AC on, it doesn't start blowing air. And when you turn it off, it won't stop blowing air.

You can't repair this issue on your own. Instead, you need to call a professional HVAC contractor. They will come over and check out the situation. Once they find out what needs fixing, they will make sure that everything gets fixed.

Evaporator coil needs to be cleaned

The evaporator coil is found on the inside unit of your AC system. Its purpose is to absorb heat from the air inside your house and cooling it with refrigerant when the blower blows air over it.

So in order for it to work properly, it's important for air to be able to pass through it. Overtime, the coils can get dusty or dirty which will restrict the airflow and put extra stress on your AC unit, decrease its performance, increase your energy consumption, and could even damage the air conditioning unit.

To check if the evaporator coil needs cleaned, look inside your inside unit with a flashlight. If the coils are covered with dirt and debris, it's time for a cleaning.

Coils are frozen

Ice could be another thing that restricts the airflow like I mentioned above. And just like with dirty coils, reducing the airflow will cause the air conditioner to work harder to maintain the temperature inside.

To unfreeze the coils, you can simply turn off the unit until the ice melts. However, if your coils keep freezing, you might have a bigger problem on your hands and you should have a professional look into it.

Coils are leaking refrigerant

As I mentioned above, the evaporator coil needs refrigerant in order to cool the air properly. When coils get older, they may start to leak the refrigerant.

If it's taking longer than usual to cool your house down, warm air is coming out of your AC when you have it set to cool, or the air coming out of your AC is blowing weak, it may be a sign that the coils are leaking refrigerant.

Unfortunately, the fix for this would be replacing the evaporator coil which needs to be done by an HVAC professional.

Dirty/clogged condenser Coil

The condenser coil is found on the outside unit of your AC system. Its purpose is to take the heat from the inside of the house and release it outside.

Since the condenser unit is located outside, it's exposed to the weather and prone to getting dirty and clogged up with debris, dirt, or grass trimmings.

A dirty or clogged condenser coil could limit the amount of heat that is removed from the air conditioning system and cause it to run longer. Hose off the condenser unit regularly to prevent this from happening.

Problems with the compressor

So to review, the evaporator coil uses refrigerant (in a gas form) to absorb the heat, and the condenser coil will release that heat into the air outside. But in order to release that heat, the refrigerant needs to be at a higher pressure. That's where the compressor comes in.

The compressor will compress the molecules in the refrigerant so that the condenser coil is able to release it outside.

Naturally, if the compressor is not working properly, the refrigerant can't get pumped through the system properly and it will disrupt this entire process which could cause your AC to keep running without actually cooling your house.

The air conditioner fan is set to on

The "auto" setting on your thermostat will automatically turn the air conditioner on and off when needed in order to reach the temperature setting that you have it set to.

However, if the fan is set to "on" rather than "auto," it will blow out cold air continuously.

This one has an easy enough fix. Simply turn the thermostat back to "auto."

Limit control switch

If your thermostat is running fine, a faulty limit control switch could be the culprit. Limit switches are used to prevent the temperature from rising too high.

Most limit controls are designed to work automatically, meaning they turn off the system when the temperature reaches a certain level. But sometimes they don't work properly, which causes the unit to run continuously.

The good news is that simply resetting the limit switch should fix the problem. To do so, open the control panel, look for the limit switch (usually either red or yellow) and push it to reset the unit.

Wiring issues

Every component of your AC system that I have mentioned above relies on electricity to work properly. So one faulty wire connection could cause a chain reaction of disruptions in everything from the thermostat to the blower fan to the condenser unit.

Fixing these wiring problems requires working with electricity, which is best handled by a licensed electrician. Trying to locate and fix the root of the wiring issue could put you at risk for electrical shock or damaging your unit.

What Can I Do to Fix an Air Conditioner That Keeps Running after Being Turned Off?

Whether the problem is because of the control board, the thermostat, any of the coils, the fan, or a wiring issue, keeping your AC unit well maintained can help fix and prevent your air conditioner from continuously running after you've turned it off.

Here are some tips for keeping your air conditioner running in top shape.

Tip #1: Always schedule routine maintenance

Regular AC maintenance and tune-ups can help extend the life expectancy of your air conditioner. In addition, annual AC maintenance and tune up are required by most manufacturer warranties.

This includes cleaning the filters and coils, checking the thermostat settings and making sure the fan blades aren’t clogged.

A dirty filter can cause your system to run inefficiently. A clogged coil can prevent airflow into the evaporator, causing the compressor to work harder. So regular maintenance can help prevent all of these problems.

Tip #2: Examine your thermostat often

A good rule of thumb is to look at your thermostat every six months. Check the battery level and give the screen a good cleaning. Replacing the battery in your thermostat once a year helps ensure that your heating and cooling systems continue to function properly.

In addition to checking the battery level, you can also check the calibration on your thermostat by taping another thermometer on the wall next to it and making sure they read the same.

If you have an older thermostat or suspect it is not working properly, upgrading to a smart thermostat may be a good idea. The new thermostats on the market come with an array of cool features and can also help save you money on your energy bill.

Tip #3: Inspect the air ducts

Air ducts are what connect the vents throughout your house. The air travels from your HVAC unit, through the ducts, and out through the vents to cool your house.

They typically run through your attic or under your house if you have a crawl space so, over time, dirt, debris, dust, and all kinds of things can make their way into the ducts.

Not only does this put the air quality at risk, it can also affect the efficiency of your HVAC system the same way that blockages in the coils can prevent it from working properly.

So inspecting your air ducts regularly will allow you to know when they need to be cleaned. It is a bit of a dirty job that is best handled by professionals and will range anywhere from $400 to $1000.

Tip #4: Check the air filter regularly

Filters play a major role in keeping your air conditioner working properly. When the filter gets dirty, it doesn't allow enough airflow across the coils, which causes your AC to work harder. Dirty filters also make your air conditioner use more power.

Air filters need to be checked monthly. Check the manual to know what type of air filter you're using and how often it needs cleaned (if reusable) or replaced (if disposable).

Changing the filter is as easy as turning off the power to your unit, opening the vent, taking out the old filter and putting the new one in. The new filter will usually have arrows indicating which direction it needs to be put in.

Tip #5: Clean blower fan

The blower fan moves air in and out of your HVAC system. If the blower fan starts making noise, it usually indicates problems with the motor or means it needs to be cleaned.

You can use a vacuum or air compressor to clean dust out of the blower fan without taking the whole unit apart, but if the fan is really dirty, you may want to call a professional to take it apart and professionally clean it.

When Should I Call a Professional?

To call a professional or to DIY – that is the common question. Regular maintenance and light troubleshooting can be done by yourself when dealing with HVAC systems.

But if the problem deals with electrical or gas, or if it requires taking your HVAC unit completely apart, I would suggest enlisting the help of an HVAC technician. For example, you can clean your evaporator or condenser coil without calling an HVAC technician.

You can even deice the coils by turning your unit off for a while. But if refrigerant leaks from the coils, professional help is advised as I mentioned before. Wiring problems and short circuits would also require help from an HVAC expert or electrician.

Repairs can get quite expensive if you need to start replacing parts. And if you need to replace the entire unit, you will have to factor in labor costs as well which can be near the $5000 - $10,000 mark.

Annual maintenance inspections are usually only around $100 - $200 which could save you money in the long run so be sure to keep up on those!