Why does my AC unit keep turning on and off?
If your air conditioner keeps turning on and off your AC system is most likely short cycling. An AC system may turn on and off repeatedly due to dirty, broken, or failing parts or for various other mechanical or electrical reasons.
The term short cycling refers to when an AC system’s cooling cycle terminates prematurely only to turn on again after a short time. Depending on indoor and outdoor conditions, this could mean that your system turns on and off every 5 to 10 minutes.
An air conditioner that is switching on and off repeatedly is bad for both homeowners and your AC system. It takes more power to start your AC over and over as opposed to when it’s running smoothly as it does in longer cycles. It also causes extra wear and tear on the mechanisms that work to turn on your AC. This can dramatically increase your electric bill and result in more repairs needed for your AC, so this is an issue you want to fix as soon as possible.
10 Reasons Your AC Keeps Turning On and Off & How to Fix It
Luckily, short cycling is usually an easy fix! Learn some of the most common reasons why your air conditioner keeps turning on and off and how you can stop your air conditioner from short cycling.
1. Thermostat Issues
Your problem may be as simple as your thermostat causing the short cycling, so when your AC system is short cycling, check the thermostat. While the thermostat may seem like one small component of your entire system, this device controls the temperature of your entire home, so it’s important that it functions properly.
If the thermostat is not sensing the temperature accurately and communicates misinformation, it will signal the air conditioning system to start and stop frequently.
If you notice your thermostat screen is blank or fading it may be low on batteries and losing power intermittently. This will cause your AC system to turn on and off when your thermostat loses battery power.
Solution: Try replacing the batteries and restarting the thermostat. If neither solution fixes your problem, call an HVAC professional to diagnose the thermostat.
2. Bad Thermostat Placement
Your thermostat measures the temperature of the air around it to determine when to turn your AC system on and off. Your thermostat may have inaccurate readings if it’s located:
- Near a window and receiving direct sunlight
- Close to a room that’s always hotter than the rest of the house, such as the kitchen or bathroom
- Beneath supply air vents, receiving direct airflow
Any of these situations could cause your thermostat to receive inaccurate, poor readings and think your house is hotter or colder than it really is.
Solution: Move your thermostat to a better, more centralized location.
3. Dirty Air Filter
Clogged air filters are one of the most common causes of AC problems. A dirty air filter restricts airflow to your AC system and can cause multiple problems, including short cycling.
Solution: Check and replace your air filters if they’re dirty.
Related article: How Often Should I Change My AC’s Air Filter?
4. Dirty Condenser Coils
If your outside AC unit is turning on and off and you haven’t performed AC maintenance in a few years, it’s possible your AC’s condenser coils are caked in dirt and debris. Condenser coils are located inside the outdoor AC unit and release the heat from inside your home. If they’re clogged with too much dirt and grime, your AC system could overheat and turn off frequently.
Solution: Clean your condenser coils or have a local HVAC company perform routine AC maintenance.
5. Oversized Air Conditioner
Have you always had this problem? Or did it only start recently when you installed a new AC system?
A system that is too large won’t have an appropriate refrigerant cycle and will face numerous problems, like cooling your home too quickly and then turning off shortly after it turns on. This might sound like a good thing, but in reality, your home is cooling unevenly and your AC will turn back on again sooner than it should need to.
Not only are these issues inconvenient, but they can cause bigger problems for your home, such as:
- Higher energy bills: Turning your AC on and off repeatedly uses more energy
- More repairs: Not only does short cycling use more energy, but it also puts more wear and tear on the parts in your AC
- Shorter lifespan: More wear and tear means the average life expectancy of your air conditioner will be shorter.
Solution: Use an AC sizing calculator to approximate your system size requirements or contact a local HVAC company for a second opinion on the installation.
6. Refrigerant Leak
If your AC system has a refrigerant leak, your air conditioner could be too low on refrigerant. Refrigerant is a coolant that cycles through your AC system, absorbing heat and cooling down the air inside your home.
It’s a common misconception that refrigerant is used up as part of an AC system’s cooling process. But the truth is low refrigerant levels are caused by small holes that allow the refrigerant to escape.
When your AC system is low on refrigerant, the compressor will malfunction and shut off your compressor because the pressure is too low. Then, when your compressor is off, the pressure will rise again and it will turn back on. This creates a short cycle that causes massive amounts of wear and tear on your AC system, potentially resulting in parts going bad or system failure.
Solution: Refrigerant leaks can be dangerous, call a local HVAC company to find and fix the leak.
7. Compressor Failure
Just like when there’s a refrigerant leak, if your AC compressor is overheating, malfunctioning, or starting to fail, it will result in your AC system shutting off frequently and starting back up shortly.
Solution: Contact a local AC repair company to diagnose and replace your AC compressor.
8. Frozen Evaporator Coils
If your AC system has airflow issues or a refrigerant leak, it’s possible your evaporator coils are freezing up. When this happens, your AC system or sometimes just your outside AC unit will turn off until the ice thaws and then turn on again.
Solution: Check your outdoor AC unit for ice buildup, if you’ve already checked your air filters, then you likely have a refrigerant leak and will want to call a local HVAC company to find and fix the leak.
Air Conditioner Turns On and Off Right Away
Is your air conditioning system turning on and off right away, after only a few seconds or minutes of running? If your air conditioning unit turns on and then off immediately then you most likely have problems with the electrical components or the run capacitor.
9. Electrical Problems
Electrical problems are a common cause of short cycling. Often times, there may be an issue with the electrical supply line or the capacitor could be broken or failing, but your AC system could also have an electrical issue due to the thermostat, electrical connections anywhere in the system, or the circuit boards.
Solution: Call a local professional electrician. Electrical problems are not only difficult to diagnose but diagnosing an electrical problem can be dangerous for even the most knowledgeable homeowners.
10. Bad Run Capacitor
Your AC’s run capacitor gives your AC system the initial boost of energy it needs to turn on and also provides continuous power so your system can keep running. When this part starts to go bad it can result in intermittent power being supplied to your AC, causing it to turn off unexpectedly and then back on.
If your outside air conditioner turns on and off right away, then chances are there’s a problem with your run capacitor.
Solution: Contact a local HVAC company to diagnose and replace your AC capacitor.