Why Does My AC Start Then Stops After A Few Seconds?

If you have an air conditioner that starts up for a few seconds and then stops, it could be due to a number of reasons. Some may be easy to fix while some may 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.

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 then stop quickly.

1)     Thermostat issues

The following thermostat issues can cause your air conditioner to keep starting and stopping after a few seconds.

Thermostat settings

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, that means it’ll only be running for a short time before stopping.

Solution

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 even after adjusting it to the correct temperature point, then your thermostat could be in the wrong location.

Poorly located Thermostat

A thermostat that is 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 that 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.

Solution

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.

2. Clogged air filters

Air filters screen out dirt and other particles that would interfere with the normal operation of your air conditioner.  Besides that, air filters also ensure that the air that is 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 you proceed to troubleshoot any other problem with your air conditioner.

3. Low refrigerant

A refrigerant commonly known as freon is a substance that is 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 located at the compressor unit will kick in to shut down the unit. This could be causing short cycling in your air conditioner.

Solution

A refrigerant runs in a closed system so it should never run out. However, a low refrigerant in your ac system means that there is 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.

4. 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 is known the size of your space, then get the correct size ac unit.

Below is a chart for sizing of AC (in Btu rating) for a specific space.

Square feetBTUs
150200
200250
250300
300350
350400
400450
450500
500600
600700
700800
800900

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.

Solution

A workable solution is to call professionals to come and access 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.

5. 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).

Solution

You’ll need to open up some panels on the outside of your house and take a 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!

Faulty control board.

A faulty control board can cause a number of 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.

Solution

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 with investigating any damages or requirements for a new control board. A call to professionals will be in order.

6. Clogged Drain Line

A drain line traps water from your air conditioner. However, when this line gets clogged, a float switch will kick in and shut the air conditioner. Each time you turn on your AC it will quickly stop. Other times, the moisture in the drain line could freeze and this could be causing the ac to be shut off after you turn it on.

Solution

 If you think your ac drain line is clogged, watch how to unclog it below

7. 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, then there may be 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 better hire an HVAC professional to come out and diagnose what’s wrong so they can fix it.

Solution

If you can open the outdoor condenser unit, open it.  But before you do so, turn off power at the main circuit breaker or at the disconnect (a small switch box) located on the 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 surely attached.

8. Bad capacitor

Some air conditioners have double single capacitors (common in older models) in the condenser unit and others have dual capacitors. Dual capacitors have two capacitors in one unit. One to start (start capacitor) the unit and the other one 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.

Solution

To fix this problem you’ll need to replace the capacitor. The more common ac capacitors are the dual models, the single capacitors were common 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 would recommend that 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.

Final Thought

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, that include, thermostat settings and the outside temperature. But if you notice that your ac starts for a few seconds and then stops, that can mean that there’s something wrong and you may want to know what’s really going on.

That said, we hope our troubleshooting guide has helped find a solution. Thank you for reading.