“My air conditioners starts OK; then it stops in seconds/minutes. What’s wrong?”
One of the most annoying (and potentially harmful) problems we encounter is air conditioner short cycling. It involves an air conditioner short cycling in seconds or minutes, without even completing a full cooling cycle.
(Example of AC short cycling) Here is what you are seeing if your AC unit is short cycling:
- You set your thermostat to let’s say 70°F.
- AC starts up OK and the indoor air handler starts blowing cold air. Everything fine thus fan.
- AC abruptly stops after 30 seconds, 1 minute, 5 minutes. This is AC short cycling; normal cooling cycling lasts for about 10 minutes.
In AC short cycling this harmful process is repeating without the AC ever reaching the 70°F thermostat setting.
3 undesirable consequences of running an air conditioner that is short cycling are:
- Higher electricity bills. AC constantly starting and stopping will draw more power. It’s akin to turning your lights on and off all the time.
- Reduced AC lifespan due to higher wear and tear. Compressor kicking in every few minutes instead of every 20 minutes or so (normal cooling cycle) will wear it down quicker. Constantly cooling down the indoor refrigerant lines increases the chances of further problems you might have as a consequence of running an AC that is short cycling in seconds or minutes.
- AC not doing its job. AC has but one purpose: to keep us cool. If the AC unit is short cycling – not completing a full cooling cycle – its cooling capabilities dampened significantly.
As with every AC problem, we will look at what might be the root cause of AC short cycling. Namely, what exactly is making your air conditioner turn on and off without completing a full cooling cycle.
To help everybody out, we will also look into how to quickly fix an AC short cycle problem:
5 Most Common Causes Of AC Short Cycling (Oversized Unit, Freon Leak, Coils, Filters, Thermostat)
These 5 most common causes of AC short cycling we’re going to cover are universal across all types of air conditioners. They are a useful resource for:
- Central air unit short cycling.
- Ductless mini-split AC short cycling.
- Window AC short cycling.
- Portable AC short cycling.
To diagnose what is wrong with our AC, we will go over air conditioner short cycling troubleshooting. With all that in mind, let’s look at why an air conditioner shuts off every few minutes (or even seconds):
#1 Oversized AC Unit Might Cause Short Cycling
An air conditioner that is too large for your home will likely start short cycling. That’s why it’s so important to correctly size your air conditioner.
Example of oversized AC unit: You have a 1,000 sq ft home and install a 5-ton (60,000 BTU) air conditioner. This will inevitably lead to AC short cycling.
How does a too large air conditioner lead to short cycling?
Essentially, every AC will have one goal: to get the room temperature to the thermostat set temperature (let’s say 70°F). If you start an AC unit at 78°F, the air handler will start blowing cold air. If the AC is adequately sized, it will blow cold air unit it reaches 70°F.
If you have an oversized AC unit, however, the AC will use all that overkill power to blast cold air very fast. In fact, the cooling output will be so fast that the cool air will not be able to distribute evenly. You will likely see 70°F in the room where the air handler is located, and 75°F or so in other rooms.
The oversized air conditioner will get a signal that the thermostat set temperature (70°F) is achieved and it will shut down immediately. This is what we call short cycling.
You’re left with uneven air temperature distribution and an air conditioner that keeps on turning on and off repeatedly. One room might be cool enough but other spaces will be hotter; and you’re wasting all that AC power, spiking electricity bills, and running the AC into early retirement.
Now, if we do have a short cycling oversized AC, there are only three things you can do:
- Run it on low cooling output. Most of you have already tried this and it didn’t work; that’s because the AC is so big that even running it on a low setting will lead to the air conditioner cycling on and off.
- Install an additional air handler (only for mini-split ACs). If your outdoor mini-split unit allows it, you can install an additional air handler. This will lead to a more even distribution of air throughout your house. Unfortunately, installing an additional air handler or zone is not an easy nor an inexpensive task.
- (Main Solution) Replace your oversized AC with a smaller air conditioner. Nobody really wants to replace an air conditioner; you already have one installed, right? If the air conditioner cycles on and off on account of it being oversized, downsizing an air conditioner is pretty much unavoidable.
How to check if your air conditioner is actually oversized?
You can use our two AC sizing calculators to adequately estimate how big an air conditioner you actually need:
This will give you a rough estimate.
Note: An air conditioner should be at least 40% bigger than what you need to start short cycling. If you have a 4-ton unit when in practice you would only need a 3-ton unit, the likelihood of air conditioner short cycling is very low.
If your AC is properly sized, it might be short cycling due to frozen evaporator coils:
#2 Evaporator Coils Are Frozen (Symptom Of Deeper Problems)
The indoor air handler contains evaporator coils. When warm air is passed over these coils, it is effectively cooled down, and we can enjoy a cool breeze coming from the AC unit.
In some cases – as a result of deeper problems within AC (compressor, fan motor, freon, leak, debris) – the evaporator coil might freeze. This will potentially lead to AC short cycling.
Why might frozen evaporative coils result in air conditioner short cycling in seconds?
When the AC starts, it wants to blow out cold air to reach the thermostat set temperature. If coils are frozen, the heat exchange (cooling of air) is virtually non-existent. It’s one of the main reasons why the air conditioner might not be blowing cold air (more about that here).
Feedback AC will get is ‘What I’m doing in not effectively lowering air temperature’ and it will shut down. In some time, it will start again and try to adequately lower the indoor temperature. If the evaporator coils are still frozen, AC will shut down again.
This can lead to the air conditioner rapidly starting and stopping. It’s one of the main reasons for air conditioner short cycling in seconds.
How to fix frozen evaporator coils?
Usually, frozen evaporator coils are just a symptom of deeper problems within your AC unit (either window, portable, or outdoor or/and indoor units in case of mini-splits). Basically, you can’t just unfreeze the coils and hope everything will be OK again.
The smartest thing is to have the AC checked out by an HVAC professional. He or she will measure the airflow, the output temperature, and check the compressor, refrigerant levels, air filters, fan motor, and so on.
#3 Clogged Air Filters Will Overheat The AC And Cause Short Cycling
Let’s be honest. Not everybody cleans AC air filters as regularly as they should. If air filters are not regularly cleaned, they can become clogged. Quite surprisingly, something as simple as air filters can lead to a number of different AC problems, including short cycling.
Clogged air filters lead to restricted airflow. Sufficient airflow is what every AC unit desperately needs to perform its function. If the airflow is restricted, other parts like the compressor and fan motor will work extra hard to achieve sufficient airflow. This can lead to overheating/exhausting of internal parts.
Air conditioners know how to secure their internal parts. If they see that – no matter what – the adequate airflow cannot be achieved, they will shut down to protect itself from overheating.
We will see that as the air conditioner starting and stopping in a minute or two. An AC will need about a minute to realize that something (clogged air filters) is blocking the airflow, and will shut down. We will see this as an air conditioner short cycling in minutes.
What we can do to stop our AC from short cycling?
All those problems might be caused by something as simple as clogged filters. Here the fix is very simple: Just unclog the air filters. That will enable for sufficient airflow, the air conditioner will know it’s doing its job, and it won’t stop before completing its full cooling cycle as below.
This is one of the simplest DIY fixes for AC short cycling.
#4 Low Refrigerant Levels Causing AC Compressor Short Cycling
Refrigerant – R22, R410A, etc. – is the coolant that is essential to air conditioners. In every air conditioner type, the refrigerant should stay in the refrigerant lines throughout the lifespan of the air conditioner.
If, however, there is a leak in refrigerant lines, the refrigerant will start oozing out. This will eventually lead to AC compressor short cycling like this:
- Refrigerant lines are pierced, causing a leak.
- Refrigerant is slowly leaking out, resulting in low refrigerant levels.
- Low refrigerant levels will affect the compressor-pressure levels, triggering the compressor’s low-pressure control.
- Compressor low-pressure control will shut down the compressor.
This will result in AC compressor short cycling; repeatedly turning on and off. In turn, we as homeowners will see our AC short cycling. Another thing we might notice is the air conditioner blowing hot air (due to hot refrigerator coils).
How to fix AC short cycling due to low refrigerant lines?
There is no way around this: Just call an HVAC professional. You would have to expose the refrigerant lines, find the leak, fix the leak, replace the refrigerant (dangerous chemicals involved), and do an air conditioner short cycling troubleshooting all on your own.
In many cases, you can do something yourself to fix your AC. We even explain how you can recharge freon in a window air conditioner, for example; with uttermost carefulness. But in this particular case, it’s best to consult an HVAC expert.
#5 If It’s Not Sizing Or Hardware, It’s Usually The Electrical System (Thermostat Issue)
If during air conditioner short cycling troubleshooting you’ve eliminated oversized AC and hardware problems, the problem must be in the electrical system.
Every air conditioner has a thermostat and a control board. Both are prone to issues that are really hard to resolve; even HVAC technicians have problems with that. If you suspect a thermostat might be an issue, you might want to call an HVAC repair company and talk to an electrician there.
The thermostat can cause AC short cycling in several different (even unpredictable ways). Wrong wiring, wire sockets not properly fixed, short circuits, and so on can lead to all kinds of AC problems, including short cycling.
This is simply a fix you can’t DIY. You can maybe check if there is a thermostat wiring; you can use our guide on how to properly wire a thermostat here.
Some HVAC Professionals You Can Call To Help You Out
If during this AC short cycling troubleshooting you didn’t get appropriate information, you should consult an HVAC professional. Or, if you now know what is causing the AC to short cycle, but can’t fix the problem (many problems need professional help), you should also call an HVAC professional.
If you need help, you can use the HVAC help network all across the US. All you have to do is to fill in this HVAC professional form, tell the problem you’re experiencing, and you’ll get some free help and even quotes from vetted HVAC professionals in your area.
Hope this helps.