AC Not Turning Off? 8 Common Causes and How to Fix Them

Quick AnswerAn AC not turning off is usually caused by a wrong thermostat setting, a dirty air filter, a frozen evaporator coil, dirty condenser coils, a stuck electrical contactor, low refrigerant, or an undersized unit. Start by switching your thermostat fan to AUTO and replacing the air filter. If the problem continues, call a licensed HVAC technician.

It is a hot Louisiana afternoon, and your air conditioner has been running for hours without stopping. The house is not getting any cooler, your energy bill is climbing, and you are starting to wonder,” Is something wrong with my AC?

If your AC is not turning off, you are not alone. This is one of the most common AC problems homeowners in Lafayette deal with every summer. The good news is that many causes are simple to fix on your own. A few others need a professional HVAC technician.

In this guide, the team at Fontenot Air Conditioning and Heating walks you through the 8 most common reasons your air conditioner keeps running nonstop, and exactly what to do about each one.

Internal Link Note: Link this article to your Pillar Page: ‘Common AC Problems’ anchor text suggestion: ‘one of the most common AC problems’

Is It Normal for an AC to Run All the Time?

First, let us clear something up. A healthy air conditioner does not cycle on and off every few minutes; this is bad for the system. Normally, an AC should run for about 15 to 20 minutes per cycle, two to three times per hour.

On a very hot day in Lafayette, when temperatures hit the upper 90s, your AC may run longer than usual. That is completely normal. The system is working harder to pull the heat out of your home.

When should you be concerned? If your AC is running for hours straight without ever turning off, and your home is not reaching the temperature you set, that is a sign that something is wrong. Let’s look at the most likely causes.

8 Reasons Your AC Not Turning Off

1. Thermostat Is Set to the Wrong Mode

This is the most common and easiest fix. Many homeowners accidentally leave their thermostat fan setting on ON instead of AUTO.

What happens: When the fan is set to ON, the blower fan runs continuously, even when the AC compressor is not actively cooling. This makes it feel like the AC never turns off, even though the unit may be cycling normally.

How to fix it:

1. Go to your thermostat.

2. Find the fan setting; it will say ON or AUTO.

3. Switch it to AUTO.

4. Set the temperature a few degrees higher than the current room temperature.

5. Wait 10 minutes and see if the system cycles off.

This simple fix takes less than a minute and costs nothing. Try this first before anything else.

2. Dirty or Clogged Air Filter

A dirty air filter is one of the top reasons an air conditioner runs nonstop. When the filter is clogged, it blocks airflow through the system. Your AC has to work much harder and run much longer to move enough cool air through your home.

Signs of a dirty filter:

• Weak airflow coming from your vents

• The air in your home feels stuffy or dusty

• Your AC runs longer than usual without cooling

How to fix it:

6. Turn off your AC at the thermostat.

7. Find your air filter, usually in the return air vent or inside the air handler.

8. Pull out the filter and hold it up to a light. If you cannot see light through it, it is time to replace it.

9. Insert a new filter with the arrow pointing toward the air handler.

10. Turn your AC back on.

Pro tip from Fontenot A/C & Heating: Check your filter every 30 days and replace it every 1 to 3 months, depending on how much dust, pet hair, or pollen is in your home. This one habit alone prevents a huge number of AC problems.

Internal Link Note: Internal link opportunity: Link ‘AC problems’ to your Pillar Page on Common AC Problems.

3. Frozen Evaporator Coil

This one surprises a lot of homeowners. Yes, your AC can actually freeze up, even in the middle of a Louisiana summer. When the evaporator coil inside your air handler ices over, it cannot absorb heat properly. Your AC ends up blowing warm air and running constantly, trying to reach your set temperature.

Signs your coil may be frozen:

• Warm or room-temperature air coming from your vents

• Ice or frost visible on the copper lines near your indoor unit

• Water dripping or pooling around your air handler

How to fix it:

11. Turn the AC off at the thermostat immediately; do not keep running it on cooling mode.

12. Switch the fan to ON to help melt the ice faster.

13. Let the coil fully defrost; this usually takes 2 to 24 hours.

14. Check and replace the air filter, since poor airflow is the number one cause of a frozen coil.

15. Turn the AC back on once fully thawed.

If the coil freezes again after you restart, you likely have a deeper issue like low refrigerant. At that point, call a professional.

4. Dirty Condenser Coils (Outdoor Unit)

Your outdoor AC unit, the condenser, releases the heat that was pulled from inside your home. When the condenser coils are coated with dirt, grass, or debris, they cannot release heat efficiently. Your AC runs longer and longer, trying to compensate.

Signs of dirty condenser coils:

• The outdoor unit feels very hot to the touch

• AC runs continuously but barely cools

• You can visibly see dirt, leaves, or debris stuck to the fins

How to clean it:

16. Turn off the power to the unit at the breaker box.

17. Remove large debris by hand.

18. Use a garden hose on a gentle setting to rinse the coils from the inside out.

19. Do not use a pressure washer; it will bend the fins.

20. Let it dry for 15 minutes before restoring power.

Fontenot Tip: Keep at least 2 feet of clear space around your outdoor unit at all times. Trim back any shrubs or plants that have grown close to the unit.

5. Stuck Contactor or Relay Switch (Electrical Fault)

Inside your outdoor AC unit, there is a small electrical component called a contactor. It acts like a switch; when your thermostat calls for cooling, the contactor closes and sends power to the compressor and fan motor.

Over time, the contactor can get stuck in the closed position. When this happens, your AC runs continuously even when the thermostat is off or set higher than the current temperature.

Signs of a stuck contactor:

• Your AC keeps running even after you turn the thermostat off

• The outdoor unit never cycles off

• You hear a buzzing or humming from the outdoor unit

WarningDo not attempt to fix electrical components yourself. A stuck contactor requires a licensed HVAC technician. Working on live electrical parts without training is dangerous and can damage your system permanently.

This is a relatively inexpensive repair, usually $150 to $300, but it must be done by a professional. If you are in the Lafayette area, the team at Fontenot Air Conditioning and Heating can diagnose and replace a faulty contactor the same day.

6. Low Refrigerant Level

Refrigerant is the substance your AC uses to absorb heat from inside your home and release it outside. If your system has a refrigerant leak, the AC loses its ability to cool your home efficiently. It will run nonstop trying to reach your set temperature, and it will never get there.

Signs of low refrigerant:

• Warm air blowing from your vents even after running for hours

• A hissing or bubbling sound near the indoor or outdoor unit

• Ice forming on the refrigerant lines

• Your energy bill has been higher than normal

Low refrigerant is not a DIY fix. It requires a certified HVAC technician to find the leak, repair it, and recharge the system with refrigerant. Simply topping off refrigerant without fixing the leak is a temporary band-aid; the leak will continue.

Internal Link Note: Internal link opportunity: If you have a page about AC refrigerant or AC not cooling, link here, anchor text: ‘refrigerant leak’.

7. Undersized AC Unit

If your air conditioner is too small for your home, it will run all day long trying to keep up, and it will never fully catch up on a hot Louisiana summer day. This is especially common in older homes where the original unit was not properly sized, or in homes that have been expanded or renovated.

Signs your AC might be undersized:

• The AC runs all day and never shuts off, even in mild weather

• Your home never quite reaches the temperature on the thermostat

• Some rooms are always warmer than others

Proper AC sizing is based on your home’s square footage, insulation, ceiling height, number of windows, and local climate. In Lafayette’s hot and humid climate, getting the right size unit is especially important. An HVAC professional can do a load calculation to determine the correct size for your home.

8. Extreme Outdoor Heat

Sometimes the simplest answer is the right one. When Lafayette temperatures push into the upper 90s or over 100 degrees, even a perfectly healthy, properly sized AC system will run longer than usual. The system is simply working hard against extreme heat.

What to watch for: If your AC is running long, but your home is still gradually getting cooler, and it eventually reaches your set temperature, your system is probably fine. But if it runs all day and the temperature inside never drops, something else is wrong.

During a heat wave, you can help your AC by closing blinds and curtains on sunny windows, running ceiling fans, and avoiding heat-generating activities like cooking during the hottest part of the day. 

Quick Reference: Causes at a Glance

Not sure which problem you have? Use this table to quickly match your symptoms to the most likely cause.

Cause	Spot the Sign	DIY Fix?	Call a Pro?
Wrong thermostat setting	The fan runs even when the temperature is reached	Yes	No
Dirty air filter	Weak airflow from vents	Yes	No
Frozen evaporator coil	Ice on the indoor unit, warm air out	Partial	If recurring
Dirty condenser coils	The outdoor unit feels hot, AC struggles	Yes (rinse)	If damaged
Stuck contactor/relay	AC runs even with the thermostat OFF	No	Yes
Low refrigerant	Warm air, a hissing or bubbling sound	No	Yes
Undersized AC unit	Never reaches the set temp all summer	No	Yes
Extreme outdoor heat	Runs more but cools eventually	Monitor	If no cooling

Step-by-Step DIY Troubleshooting Guide

Before you call a technician, work through these steps in order. Many homeowners solve their AC problems in under 10 minutes with these checks.

21. Check your thermostat. Make sure it is set to COOL, and the fan is on AUTO, not ON.

22. Raise the set temperature. Set it 5 degrees higher than the current room temperature and see if the unit cycles off.

23. Inspect the air filter. Replace it if it is dirty or clogged.

24. Check your outdoor unit. Make sure it is not surrounded by debris, vegetation, or standing water.

25. Look at the indoor unit. Check for ice or frost on the coils or copper lines.

26. Check all vents . Make sure furniture or rugs are not blocking any supply or return vents.

27. Reset the system, turn off the AC at the thermostat, flip the circuit breaker off for 30 seconds, then turn it back on and restart.

28. Call Fontenot A/C & Heating. If none of the above steps work, it is time for a professional diagnosis. 

When to Call a Professional

Some AC problems are safe and easy to fix yourself. Others need a licensed HVAC technician. Here is a simple breakdown:

You can handle it yourself:

• Switching the thermostat from ON to AUTO

• Replacing a dirty air filter

• Clearing debris around the outdoor unit

• Rinsing off dirty condenser coils with a garden hose

• Resetting the circuit breaker

Call a professional:

• The AC runs even with the thermostat turned off (stuck contactor)

• You suspect low refrigerant, hissing sounds, warm air, and ice on lines

• The evaporator coil freezes repeatedly after you thaw it

• Your home never cools down, no matter how long the AC runs

• Strange burning, grinding, or rattling sounds from the unit

• Your AC is more than 10 to 15 years old and has frequent issues

Serving Lafayette and the Surrounding AreaFontenot Air Conditioning and Heating has been helping Lafayette homeowners keep their AC systems running right for years. Whether you need a quick diagnosis or a complete system replacement, our licensed technicians are ready to help. Call us today for fast, honest service.

Frequently Asked Questions

How to Prevent AC Problems Before They Start

The best way to avoid an air conditioner that won’t turn off or any AC problem is regular maintenance. Here are the habits the team at Fontenot Air Conditioning and Heating recommends for every Lafayette homeowner:

• Replace your air filter every 30 to 90 days, depending on your home.

• Schedule a professional tune-up once a year, ideally in the spring before summer heat arrives.

• Keep the area around your outdoor unit clear of plants, debris, and fencing.

• Rinse off the outdoor condenser coils once a year with a garden hose.

• Use a programmable or smart thermostat to set consistent temperatures.

• Keep all supply and return vents open and unblocked.

• Check your condensate drain line once a season to prevent clogs.

A little routine maintenance goes a long way toward keeping your system running efficiently and avoiding expensive repairs down the road.

Bottom Line

An AC not turning off is almost always a sign that something in your system needs attention. In many cases, like a wrong thermostat setting or a dirty air filter, you can fix it yourself in a few minutes. In other cases, like a stuck contactor, low refrigerant, or a frozen coil that keeps coming back, you need a licensed HVAC professional.

If you have tried the basic troubleshooting steps and your AC is still not turning off, do not keep running it and risk making the problem worse. The team at Fontenot Air Conditioning and Heating in Lafayette is ready to help. We diagnose fast, explain everything clearly, and fix it right the first time.

Ready to Get Your AC Fixed?Contact Fontenot Air Conditioning and Heating today. We serve Lafayette and the surrounding communities with fast, reliable HVAC service. Do not sweat it out, call us now.