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If you have an air conditioner that starts up for a few seconds and then stops, it could be for several reasons. Some may be easy to fix, while others require a professional’s touch. Below are some causes of the problem and how to troubleshoot them.
If an air conditioner keeps turning on and off after a few seconds, this is called short cycling. Under normal circumstances, an air conditioner has a regular on and off-cycle that depends on the thermostat setting and the outside temperature.
Reasons Short Cycling Occurs
Some things that can cause short cycling of your air conditioner include thermostat issues, dirty air filters, low refrigerant, dirty coils, a poorly located thermostat, low refrigerant, and an oversized air conditioner.
So, let’s look at these issues that cause your air conditioner to start and stop after 30 seconds to a few minutes.
1) Thermostat issues
The following thermostat issues can cause your air conditioner to start and stop after a few seconds.
If you recently installed a new air conditioner, it is possible that the thermostat is not set correctly. The air conditioner will shut off when it reaches the desired temperature. If the set point is high, it’ll only run for a short time before stopping.
Check the setting on your thermostat to make sure it’s not set too high if it is set to “cool,” change the point to a much lower point (if possible, set it to the lowest point), and watch how the unit will respond when it turns on again. If it stops a few minutes later, your thermostat could be in the wrong location, even after adjusting it to the correct temperature.
2) Poorly located Thermostat
A thermostat located too close to the air vent could cause short cycling. This is how it can cause your air conditioner to stop a few minutes after it starts.
When you turn on your air conditioner, the cold air that blasts through the vent will quickly reach your thermostat (which will think that the surrounding air is cool), and that will cause it to wrongly detect the required temperature point has already been reached.
That will cause your air conditioner to stop, but the surrounding air will warm up the thermostat soon, and the air conditioner will turn back on shortly.
If the air conditioner is not installed in an ideal location, for example, too close to an air vent, you may need to relocate it to a better position. It’s best to call a professional who can come and assess the best spot for your thermostat in your home.
3) Clogged air filters
Air filters screen out dirt and other particles that would interfere with the regular operation of your air conditioner. Besides that, air filters also ensure that the air recirculated back into your home is cleaner. It’s common for clogged air filters to cause short cycling in a furnace but rarely does in an air conditioner. But as a good practice, ensure they are clean before troubleshooting any other problem with your air conditioner.
4) Low refrigerant
A refrigerant known as freon is a substance used in your air conditioner system to carry away the heat from your home to the outside environment. If this substance leaks out, a low-pressure switch at the compressor unit will kick in to shut down the unit. This could be causing short cycling in your air conditioner.
A refrigerant runs in a closed system, so it should never run out. However, a low refrigerant in your ac system means a leak somewhere. To fix the problem, the leak must be sealed before recharging your air conditioner with more refrigerant. For this fix, you may need to call in professionals for help.
5) An oversized air conditioner
An oversized AC will cool your spaces too quickly and stop before dehumidifying the air. It will start again and stop a few minutes later. The problem of short cycling is common among oversized air conditioning systems.
The first thing you want to do before buying a new AC has known the size of your space, then get the correct size ac unit.
Below is a chart for sizing AC (in Btu rating) for a specific space.
See this BTU guide for 5000 sq ft.
These figures are estimates based on an average room with 2 windows, 1 door, and an 8-foot ceiling. Other variables still have to be taken into consideration before making a final decision on what size of AC you should buy.
A workable solution is to call professionals to come and assess what size of an air conditioner is needed for your home. If you just bought a new air conditioner, you may try to get a refund and have a professional do a Manual J Heat Load Calculation to determine the size that’s needed for your home.
6) Dirty condenser coils
If you’ve already checked your thermostat settings and they’re fine, there may be something blocking or restricting airflow through your condenser coils (the coils outside of your home that cool the refrigerant).
You’ll need to open up some panels outside your house and look at them to see what could be causing the issue and clean it out if necessary. Oftentimes, just cleaning these will fix the problem instantly!
7) Faulty control board
A faulty control board can cause several problems with any HVAC system. The control board is like the brain of the HVAC system. It receives cooling instructions and relays them to any other part of the cooling system.
Some problems with control boards can range from a simple blown-out fuse on the board to more complex problems.
A faulty control board can sometimes be fixed by simply resetting your HVAC system at the circuit breaker or at the switch located near the furnace (a switch that looks like a simple light switch).
If that does not fix the problem, a replacement would be necessary. Professionals can help investigate any damages or requirements for a new control board. A call to professionals will be in order.
8) Clogged Drain Line
A drain line traps water from your air conditioner. However, a float switch will kick in and shut the air conditioner when this line gets clogged. Each time you turn on your AC it will quickly stop. Other times, the moisture in the drain line could freeze, causing the ac to be shut off after you turn it on.
If you think your ac drain line is clogged, watch how to unclog it below
9) Loose wiring at your condenser unit.
It’s not uncommon for wires to wear out or corrode in your condenser unit. When wires become loose, they will be tripping and cutting power to components of your ac unit.
If none of these fixes work for you, you may have a problem with wiring at your capacitor (where energy is stored) or compressor terminals (where energy is created).
For this diagnosis, You may be able to fix it all by yourself or hire an HVAC professional to come out and diagnose what’s wrong so they can fix it.
If you can open the outdoor condenser unit, open it. But before you do so, turn off power at the main circuit breaker or the disconnect (a small switch box) located outside near the point where refrigerant lines get into your home.
Inspect the wires and look out for any worn-out loose wires. Try to put a tug on each wire connection to ensure they are attached.
10) Bad capacitor
Some air conditioners have double single capacitors (standard in older models) in the condenser unit, and others have dual capacitors. Dual capacitors have two capacitors in one unit. One to start the unit (start capacitor) and the other to provide energy to keep the ac running (run capacitor).
If any of these capacitors malfunction, they could cause the air conditioner to short cycle (to stop a few minutes after starting).
When any of the two capacitors start to malfunction, they can send intermittent power to the ac system, and that could cause it to turn on and off unexpectedly.
To fix this problem, you’ll need to replace the capacitor. The more common ac capacitors are the dual models; the single capacitors were standard in the older models of air conditioners. If your ac is one of the older modes, you can still replace it with the dual capacitor.
I recommend you call a professional to check your unit and assess if there is a need for a capacitor replacement. You should only do it yourself if you know what you are doing. Capacitors can have a high voltage that can be dangerous to handle.
Your AC is designed to turn on and off at preset intervals as part of its thermostat programming. These intervals(cycles) depend on many factors, including thermostat settings and the outside temperature. But if you notice that your ac starts for a few seconds and then stops, that can mean something wrong, and you may want to know what’s really going on.
We hope our troubleshooting guide has helped you find a solution. Thank you for reading. If you have any questions, please ask them in the comments section below.
HVAC tech with over 30 years of experience. Retired and doing repair work on the side around Madison County, AL.