AC Short Cycling: Why Your AC Turns On and Off Repeatedly?

Air Conditioner Turns On and Off Right Away

What is going on if your AC turns on and off repeatedly?

Probably nothing good. But how bad it is can be determined with a little troubleshooting. If your weather is extreme, it might be normal too.

The condition is known as short cycling.

Why Does AC Turn On and Off Quickly or Frequently

In this guide, we do some AC troubleshooting why the AC turns on and then off quickly.

Describing short cycling: The AC system, including our air handler or furnace might turn on and then turn off after just a few seconds to maybe 10-15 minutes.

Then, from a few seconds to a few minutes later, the cycle repeats itself.

Part of AC troubleshooting is to know what “normal” is. If this is a new AC – or you’re new to it because you just moved into a house, it will be helpful to know how an AC normally cycles.

How often should an AC turn on and off? 3-7 Times per hour when the air conditioner is the right size.

How frequently a properly sized system turns on an off depends on several factors.

  • A single-stage AC will cycle more frequently than a two-stage or variable capacity air conditioner.
  • An AC that is barely large enough will cycle more often than one that is almost too big. There is variation even when the unit size is within acceptable parameters.
  • The hotter it is outside, the more frequently it might cycle.
  • Other variables include house size and layout and how well your home is insulated.

Even if it is cycling more than 7 times per hour, it might not technically be a short cycling AC.

Is it brutally hot outside? Is the humidity level really high? Both? If so, your AC just might be working really hard to keep up with extreme conditions.

Of course, if it’s only staying on for a few seconds and shutting off – and especially if your home is warmer than the thermostat set point, that’s not normal for a correctly sized AC.

Common Reasons your AC Won’t Stay On

Here are problems for you to troubleshoot.

1). Your AC Refrigerant is Low

AC Refrigerant is Low

As air conditioner parts get old, they wear like anything else. Eventually corrosion might cause a refrigerant line fitting to leak.

When it does, the unit no longer has enough refrigerant to carry sufficient heat from your home. It cycles, removes some heat and shuts off, but the thermostat is soon calling for AC again. The AC turns on and off repeatedly.

To troubleshoot, consider if this is a recent issue – even if the weather has been stable. If it seems to be sudden, this is a short-list suspect.

You can also look for obvious corrosion or damage to the copper refrigerant lines or stains on the ground near them. The lines should be insulated, so check for obvious damage to the insulation.

Maybe someone hit one while cutting the grass or playing in the yard?

If it is a tiny leak, the refrigerant will leak out, evaporate and not leave a trace.

Is the AC new? Was it recently serviced? An inexperienced technician might have damaged or kinked a line while installing

SolutionThe refrigerant line and/or fittings will need to be repaired or replaced depending on the issue. Once the lines are sound, the AC will be charged with refrigerant. This isn’t a DIY repair. A refrigerant certification – a refrigerant card, as it is called – is required to handle and dispense/dispose of refrigerant.

Pro Tip: If you suspect a refrigerant leak, call an HVAC company or our toll-free number pronto. A short cycling AC caused by low refrigerant can quickly damage the compressor, and that’s a costly invoice.

2). The Compressor is Going Bad

AC Compressor

Yep. Nobody wants to hear this one, especially anyone who has received a compressor replacement cost estimate.

According to our AC Repair Guide, compressor replacement price starts at more than $1,000 for most models and can top $2,000. It’s probably time for a new AC. Even if the compressor is under warranty – most are 10 years but a few brands offer Lifetime warranties – labor isn’t covered.

Did you know that? The cost of labor for AC repair is the homeowners responsibility after the first year – up to 3 years on a couple Carrier/Bryant models.

To troubleshoot an AC compressor, listen to it. They herk and jerk a bit when operating normally, but if its really clanking or rattling, it is probably worn out and ready to quit.

SolutionEven if under warranty the cost of labor might exceed $1,000. And if the AC is older, putting the cash into a brand-spanking new unit, a more efficient one, should be considered.

3). Coil Freeze Up

Coil Freeze Up

While not the most common, this is the easiest fix in some cases.

Your outside unit has a coil – it has fins on it light a radiator.

We’re talking about the indoor coil, which a lot of homeowners didn’t realize was there.

The indoor coil, aka the evaporator coil, is inside the furnace or air handler cabinet or might be tucked into the plenum or have its own small cabinet.

You can find it by following the refrigerant lines coming into and out of the house.

The cause of AC coil freeze up can be simple and cheap or a little more costly.

Troubleshooting starts by checking the air handler or furnace filter. Is it nasty dirty?

When there isn’t enough airflow through your HVAC system, the evaporator coil gets cold enough to freeze. When it does, it can cause short cycling as the system struggles to function properly.

SolutionChange the air filter and let the system thaw on its own or with the help of the HVAC blower running on the thermostat Fan setting and pulling warm air over it.

Pro Tips: Prepare for melting ice! When the freeze up melts, the water amount might overwhelm the coil drain pan and drain. If there is a potential for water damage based on the coil’s location, be ready to soak it up with towels.

Can I chip the ice off the coil? Some readers want to speed the process. We don’t recommend it because it is easy to damage a coil. Crack the line, and you’ve got a $1,500+ job on your hand. Some AC coil replacement costs more than that.

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4). The AC is Too Big

Air conditioning cycles are supposed to be long for even cooling and better humidity removal in muggy summer weather.

When the size of the system is too large, it cools the air too quickly and shuts off. Because your house – the warm walls, floors, furniture, etc., don’t cool, the heat they hold quickly heats the air, and the thermostat senses the heat and turns the system. AC short cycling begins again.

Troubleshooting starts with an answer to this question – Does the air in your home sometimes feel cool and clammy? An AC that is too large cools the air without removing much humidity – cool and clammy air results.

SolutionIt’s best to get the system checked. The technician will inspect the system for other common reasons the AC turns on and off repeatedly.

The technician might want to do a Manual J or other type load calculation. It’s a formula that evaluates house, climate and other factors to determine the right size unit for your home.

If the AC is too big for the house:

  • It was too big from the start – a common AC contractor error. If the unit was recently installed, contact the installer and show them the report from the tech that inspected it. An ethical installer will admit their error – they should have done a load calculation – and replace the wrong size unit with one that is properly sized.
  • Your home’s energy efficient upgrades like added insulation, Energy Star windows, doors or roofing, might mean the current AC was the right size, but now it is too big. It is common that when a load calculation is done during AC replacement, the new AC should be smaller than the old. That’s a good thing, and a good reason to make energy efficiency upgrades to your home.

5). Bad Thermostat Location

Was the thermostat installation DIY?

Not to point fingers, but if the thermostat was installed in a “wrong” spot, it can cause this issues.

Near an air duct: OK, the AC kicks on and starts to cool your house by removing heat energy. The cool air flows out of the grate and hits the thermostat, quickly lowering its temperature. The thermostat is satisfied, and shuts off.

But the air surrounding it isn’t cool and immediately warms up the thermostat. It calls for AC, and the AC short cycling begins again.

In the sunshine: This is the problem in reverse.

Does morning or evening sun hit the thermostat? The unit will warm up, and the thermostat will turn on the AC even when most of the air in the house is cool. The thermostat will soon cool off and turn the AC off – at least until the sunlight warms it up again.

The thermostat also should not be located near a stove or other device that might make it artificially warm or on an exterior wall.

SolutionMove the thermostat to an interior wall where it won’t get sunlight or blasts from the AC/heat ducts or otherwise be artificially heated.

Need an HVAC Pro?

If you know what the problem is and it requires a pro to repair or if you haven’t been able to troubleshoot the AC problem, it is probably time to talk to an air conditioning professional.

If you don’t know who to call, our Free Local Quotes service is available at no cost to you. You’ll be contacted by experienced and knowledgeable AC professionals that can determine why your AC turns on and off repeatedly and what the cost-effective solution should be.

Also Read: Outside AC Unit Not Running But Inside Is

Written by

Rene has worked 10 years in the HVAC field and now is the Senior Comfort Specialist for PICKHVAC. He holds an HVAC associate degree and EPA & R-410A Certifications.

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