Why Does My AC Not Turn Off?

July 07, 2017

If your air conditioner is running non-stop, 3 situations you might be dealing with include:

  1. Your AC system is fine but your thermostat is set incorrectly

  2. There’s a problem in your AC system that’s preventing it from cooling your home

  3. There’s no problem, it’s just an abnormally hot day

Want to know which problem you have? Start by determining whether it’s just your AC fan that’s blowing non-stop or if the outdoor unit is also running.

Need a professional to fix the problem ASAP? Just contact us and we’ll send one right over.

If it’s just your indoor AC fan that’s running….

...you likely have a thermostat that’s set incorrectly or needs to be replaced.

Follow these steps to troubleshoot your thermostat:

1. Make sure the thermostat fan setting is set to AUTO not ON.

On Vs Auto

Why? Because if the fan setting is set to ON, that means the AC fan runs non-stop—even when your AC system isn’t cooling the air.

Related: 3 Thermostat Mistakes That Are Costing You $$$ This Summer

However, if the fan is set to AUTO, it runs only when during cooling cycles. If you’ve set the fan setting to AUTO but it’s still running, your fan limit switch might be set incorrectly (see step 2 below).

2. Make sure the FAN LIMIT SWITCH is set to “AUTO”, not “MAN” (manual)

The fan limit switch is actually located on your indoor air handler (so this might be tricky to do on your own). You can usually find the indoor air handler in an interior closet or attic. Look for a white push-pull button and make sure that it’s set to “AUTO” not “MAN” (manual).

The fan limit switch is basically the “master” switch that turns your AC blower on and off. So, even if you set your fan to AUTO at the thermostat, your blower fan will run non-stop if the fan limit switch on the air handler is set to manual instead of AUTO.

If your AC fan keeps running after setting the fan limit switch and the thermostat fan setting to AUTO, have a professional check your thermostat for a shorted thermostat wire.

If both the indoor and outdoor AC units are running…

...there’s likely a problem in your AC system that’s preventing it from either cooling your home correctly or shutting off after cooling down your home.

To troubleshoot an AC system that’s constantly running, check for:

1. A bad thermostat or thermistor

Your thermistor is a sensor that detects the room’s temperature. When working together properly, your thermostat and thermistor monitor the temperature of your home and send/stop voltage to both your indoor and outdoor units to turn it on/off.

But if either the thermostat or thermistor is defective, it might not be sending the TURN OFF signal to your indoor and outdoor units when it should.

What to do: Raise the thermostat until the set temperature is at least 5 degrees higher than the current room temperature. If the AC doesn’t shut off in a few minutes, have a professional repair or replace the thermostat or thermistor.

2. A dirty filter

A dirty air filter restricts the amount of warm indoor air that your system can “breathe” in. And the less warm air it can take in and cool, the longer your AC will take to cool off your home. In most cases, a dirty air filter can lead to an AC that never stops running. However, in severe cases, a dirty air filter can even kill your AC altogether.

Related: Dirty Air Filter: How It Will Kill Your Home’s AC

What to do: Check your AC filter and replace it when it looks like the filter to the right (in the picture below).

Replace your filter if it looks like the one to the right.

3. Dirty evaporator coils (or frozen)

Your indoor air handler contains evaporator coils that absorb the heat and moisture from the air inside your home. But if those coils are dirty, they can’t absorb as much heat from the air.

The result? Air gets pushed back into your home but it’s not as cool as it could be, meaning your AC has to run longer than usual.

And the worst part? Over time, dirty evaporator coils can freeze over which makes your AC system even less efficient and can eventually destroy your compressor.

What to do:Have a professional clean your condenser coils if they are dirty.

4. Leaky ducts

If your air ducts are leaky, your AC will have to work a lot harder and longer to cool your home.

You see, your AC blower fan pushes cold air through your ducts and into your home. But if there are leaks in the ductwork, you’ll lose a good portion of cold air as it escapes into the attic, basement or other unconditioned areas of the home.

Cold air can leak out of holes in your ductwork and into the attic instead of blowing into your home.

Don’t think you have leaky ductwork? Think again. According to Energy Star, the typical home loses 20% to 30% of conditioned air to leaks in their ductwork.

What to do: Have a professional inspect your ductwork for leaks and, if needed, they can seal your ducts to prevent leakage.

5. Dirty condenser

Your indoor AC unit absorbs heat from the air inside your home and then sends that heat to your condenser (outdoor unit) where it’s dumped into the outdoor air.

But if the condenser coils are dirty, it can’t “dump” that heat as fast or as efficiently as it should which means your AC takes a lot longer to cool your home.

Dirt and debris on these condenser coils can cause the AC to run non-stop.

What to do: Check your outdoor unit. If it’s dirty, use your hose (on a gentle setting) to spray off any dirt or debris on the condenser coils. Also, make sure any shrubbery, fences, etc. are at least 3 feet from the condenser coils.

Related: Why You Should Wash Your AC’s Outside Unit Before Summer Starts

6. Refrigerant leak

Refrigerant is the special liquid that absorbs heat from the air inside your home. During normal operation, refrigerant runs throughout your AC system in closed coils. But, over time, those coils can develop cracks that allow refrigerant to leak out. And when that happens, your AC will struggle to cool the air inside your home and may run non-stop to try to reach your set temperature.

Signs of a refrigerant leak include:

  • Higher-than-normal electricity bills

  • Ice on refrigerant lines

  • A frozen evaporator coil

  • Bubbling or hissing noises coming from refrigerant lines

  • Your AC struggles to cool your home

What to do: If you see the signs above, have a professional locate and repair the leak and then recharge your system with more refrigerant.

7. An undersized AC unit

If your AC unit is too small for your home, it could run non-stop and still never reach your set temperature.

You see, air conditioners are NOT a one-size-fits-all product. In fact, there’s an entire methodology that professionals use to correctly size an AC for a home (called the “Manual J”).

So what happens when your AC isn’t correctly sized for your home? Well, air conditioners are sized according to how much heat they can remove within a certain time. So if your AC is too small, it might be removing heat just as quickly as heat is coming into your home (think of it as trying to blow up a leaky air mattress).

What to do: If you think your AC might be sized too small for your home, have a professional inspect your unit and your home. If they determine that your AC is too small, they’ll give you options for upgrading your AC system.

If it’s just a really hot day…

...there’s likely not even a problem with your AC system or thermostat.

If your air conditioner runs non-stop only on abnormally hot days, your unit is probably completely fine. You see, ACs are only designed to keep up with outdoor temperatures that your location stays below for 99% of the time.

For example, in Topeka, Kansas, outdoor temperatures stay below 96 degrees 99% of the time. So as long as the temperature is below 96 degrees, your AC should be able to cool your home efficiently. But if the outdoor temperature exceeds 96 degrees, you may notice that your AC has to run non-stop just to keep your home comfortably cool.

Have an AC that runs non-stop? Get help from a Kansas City tech

If your air conditioner won’t turn off, just contact us for help.

We’ll send over a professional who can determine whether there’s a problem or not and offer professional solutions.


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