I have experienced countless service calls as a licensed HVAC contractor where the air conditioner keeps running after temperature is reached — or the AC blower just won’t shut off.
Sometimes an AC that won’t turn off is as simple as the wrong thermostat setting, but most of the time there’s an electrical or mechanical failure such as a faulty high limit switch that makes it continuously.
It may be easily be corrected by flipping a switch or it can be more complicated and you may need professional assistance.
10 Reasons Your AC Won’t Shut Off
- Electrical Issues
- Faulty Thermostat
- Wrong Thermostat Settings
- Faulty Fan Limit Switch
- Dirty Condenser Coils
- Frozen Evaporator Coils
- Dirty Air Filter
- Low Refrigerant Levels
- Low Fan Speed
- Incorrect System Size
Reason #1: Electrical Issues
Air conditioners are full of electrical parts that can fail.
You may have a fan relay stuck causing your indoor blower to run constantly even when the thermostat is satisfied.
I also see a lot of stuck AC contractors that cause the outdoor unit to run continuously as well. A stuck contactor will usually cause your coil to freeze up as well and create additional issues you have to deal with.
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Reason #2: Faulty Thermostat
Thermostats read the temperature in the house and close switches to tell your AC when to turn on.
Over time the contacts on the switches may fail or your thermostat may begin misreading temperature in which case it would need replaced.
Reason #3: Wrong Thermostat Settings
Most thermostats have a button or switch for your indoor fan. If this switch is in the “on” position, it will run all the time and won’t turn off at the set temp.
The air from the vents will be warm or room temperature because your condenser is not running, only the indoor blower is running.
Your thermostat may even be set to heat. It may seem like an obvious issue, but I’ve seen it multiple times on service calls.
The temperature never reaches a set point because it’s calling for heat and not ac.
Reason #4: Faulty Fan Limit Switch
Some furnaces have a fan limit control switch that has a manual override setting.
So even if your thermostat is set correctly, the switch overrides and runs the fan constantly. Simply resetting this switch will allow your fan to cycle properly again.
Reason #5: Dirty Condenser Coils
Your outdoor unit is called the condenser. It’s where the compressor compresses the refrigerant and pumps it through the outdoor coil.
Air from the outdoor fan is moved through that coil to exchange heat from the house.
When your coil is dirty or clogged, it greatly reduces the amount of heat that can be removed and can cause your unit to run longer run cycles while it tries to cool your home.
Removing debris like grass clippings, pollen, dust and dirt can greatly reduce your energy consumption and lower the length of time it takes for your house to cool.
Reason #6: Frozen Evaporator Coils
Airflow issues and refrigerant issues can cause your evaporator (indoor) coil to freeze up.
When this happens, your AC no longer cools effectively because it can’t move air through the ice on the coil. You may feel warm air or no air from your vents when this happens.
This can also happen when your air conditioner compressor won’t turn off because of a stuck contactor.
RELATED: Why Is My AC Unit Freezing Up?
Reason #7: Dirty Air Filter
Restricted airflow from a dirty or clogged filter almost always causes your AC to run continuously.
It freezes the evaporator coil and causes your system to work way harder than it needs to.
Reason #8: Low Refrigerant Levels
Air conditioners are designed with specific amounts of refrigerant to properly cool your home and operate effectively.
Leaking refrigerant lines or coils allow coolant to leak out and reduce the capacity that your system can cool.
Without proper refrigerant levels, your system cannot effectively transfer heat from your home and will cause it to run very long run cycles.
Reason #9: Low Fan Speed
Most indoor blowers today have multiple speeds to choose from and can also get dirty.
If your blower is not moving enough air through your indoor coil and through your duct, it cannot cool your home in a timely manner. You may still feel cold air from the vents, but it may not turn off at the set temp.
Reason #10: Incorrect System Size
Air conditioners are sized with a specific amount of heat they can remove from your home, referred to in “tons”.
One ton is 12K BTU. If your system isn’t sized correctly and is too small, it won’t have the capacity to remove the amount of heat in your home and the HVAC won’t shut off.
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There are several things you can try at home first before calling a professional to check things out.
Solution #1: Adjust Thermostat Temperature Settings
If the temperature in the house is higher than the set point on your thermostat, your air conditioner won’t turn off.
Try increasing the temperature on your thermostat above the room temperature to see if your AC will shut down on its own.
Solution #2: Adjust Thermostat Fan Settings
Make sure it’s not just the indoor unit that won’t shut off. Ensure the fan switch is in “auto” so that it only runs when there is a call for cooling.
With the temperature set point above the actual temperature, the fan should shut down as well.
Solution #3: Remove Thermostat From Wall
An easy way to determine if you have a bad thermostat is by removing it from the backplate.
This is a very quick and easy way to see if your thermostat is causing your fan or condenser to run when they shouldn’t be.
Solution #4: Eliminate Airflow Restrictions
Remove and replace your air filter and determine if there are any other potential airflow restrictions.
Check your condenser coil and wash it with a garden hose to remove any build up or debris.
RELATED: How To Add Freon To Home AC?
Solution #5: Check Your Capacitor
Your indoor fan may be running but the outdoor unit may just buzz real loud and not do much else.
This is pretty typical of a bad capacitor. These small parts can pretty easily be tested and replaced. Follow these steps to diagnose a bad capacitor:
- Disconnect power from the outdoor unit.
- Remove the access panel.
- Remove and mark the three wires going to the capacitor.
- Using a volt meter for microfarads, test from “C” to “Herm” and “C” to “Fan”
- If your readings are significantly lower than they should be, replace the capacitor.
Solution #6: Clean Your Blower Fan
A dirty blower wheel slows down the airflow and can cause your AC to struggle to keep up. To remove and clean your blower, follow these steps:
- Turn power off to your indoor unit.
- Remove the access panel.
- Remove circuit board, if applicable, keeping wires connected and move to the side.
- Remove screws for the blower housing and slide out of the cabinet.
- Using a soft brush and vacuum, remove build up and debris from the blower wheel.
- Reinstall blower and secure with screws. Reinstall circuit board and access panel. Restore power and test system.
Solution #7: Check Your Contactor
AC contractors open and close frequently. Sometimes the contacts stick or weld closed and cause your outdoor unit to run continuously.
If you turn power off to your indoor unit and your outdoor unit stays running, you definitely have a stuck contactor.
You can turn power off to the outdoor unit by using the circuit breaker or service disconnect. Once power is off you can replace the contactor or call a professional to take care of this for you.
Read Also >> Why Is The Air Conditioner Frozen?
Frequently Asked Questions
How Do I Manually Turn Off My AC?
You can switch your thermostat to the “off” position to manually turn off your AC.
If that doesn’t work, there should be a service disconnect outside that you can use. Or you can use the circuit breaker in your breaker panel.
Why Is My AC Still Running When I Turn It Off?
Either your indoor blower is running because of a thermostat issue or stuck relay, or your outdoor unit has a stuck contactor causing it to run continuously.
Some thermostats and circuit boards have built in delays that may keep your blower motor running for up to two minutes once the thermostat satisfies, but will eventually shut down.
Why Is My AC Running All Day?
A typical run cycle should last 15-20 minutes and then your AC should shut down. It may kick on 2-3 times every hour depending on how warm it is outside.
If your system stays on and runs constantly, its probably in need of some regular maintenance, or something is faulty and needs repaired.
How Long Can An Air Conditioner Run Continuously?
There is no set time an air conditioner can run. It’s a piece of equipment and as long as it’s receiving power, it will continue to run until it wears out and fails.
Unnecessary run time greatly increases wear and tear and will most definitely damage your AC.
Air conditioners need to be maintained on a regular basis to prevent breakdowns. Dirty filters and coils will cause your AC to run a lot longer than necessary.
There’s a lot you can do on your own to help keep your system running efficiently, but if you feel in over your head or uncomfortable, definitely call a professional to get your AC running at peak performance.
I hope you enjoyed this article! Thanks for reading!