What is air conditioner short cycling, what causes it, and how do I fix air conditioner or heat pump short cycling on and off?
Here we define air conditioner short cycling and we give a complete list of all of the causes of short cycling along with repair suggestions.
This article series explains how to diagnose an air conditioner or heat pump that is not cooling: this article explains how to diagnose and correct air conditioning problems like lost or reduced air conditioner cooling capacity, reduced or no cool air flow, reduced or no actual lowering of the air temperature, or an air conditioner that won't start.
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Short cycling means that your air conditioner turns off and on too often, too rapidly, or at irregular intervals. That frequent on-off switching will ultimately damage the compressor motor, fan motor, controls, or other components, leading to system failure and costly repairs.
These specifics will help you decide if your air conditioner is short cycling or operating normally.
Air conditioner short cycling in minutes: If your air conditioner turns off and back on at intervals of less than five minutes it is short cycling and needs repair.
If your air conditioner turns on and off at intervals of less than ten minutes it is probably short cycling and also deserves a service call.
Air conditioner short cyclingin seconds: Watch out: A "short cycling" air conditioner or heat pump compressor/condenser unit that turns on and then back off after just a few seconds is in serious trouble.
You should turn off the system and call your HVAC service company for repair. [Don't call us here at InspectApedia.com. We do not sell any product nor service.]
Irregular on-off A/C cycling: A short cycling air conditioner may also be heard running at irregular intervals over the course of an hour or so even though the indoor thermostat settings have not changed.
The compressor/condenser unit is the air conditioner or heat pump equipment that is located outdoors, such as shown in our photos.
The good news is that some of these AC short cycling causes are trivial to repair and thus not costly. Some, like a dirty air filter or dust-clogging a thermostat can be addressed by the homeowner.
Other air conditioner short cycling problems require help from your HVAC service technician.
For each short cycling cause or condtion we link to a more-detailed diagnosis and repair article.
If your AC system is properly sized, on an average day during the cooling season your unit will be working about half-time, or at about 50% of its cooling capacity.
While the actual "on" time of your air conditioner will vary for other reasons such as the indoor air handler unit's fan speed and cooling coil cleanliness, outside you will typically hear or see the compressor/condenser motor turn on for about ten minutes, then remain off for about the same length of time (10 minutes) before it turns on again. A 20-minute on-off cycle would also be normal and just fine.
In sum, if your air conditioner or heat pump runs for ten minutes, twenty minutes, or longer, turns off, then after a similar time interval it turns back on, your air conditioner is not "short cycling".
During very hot weather your air conditioner system may run just about constantly. If it is producing cool air the system is probably working normally. If, however your AC unit seems to never turn off, see the diagnostic details at LONG-ON CYCLING AC COMPRESSOR..
If your air conditioner is running but your home is not getting cool, see LOST COOLING CAPACITY.
Joe said: short cycling air conditioner compressor diagnosis: I have the same problem as Mathew: my A/C compressor cycles on and of every ~10 seconds. I is about 5yr old. What can we do to fix this system. Please help. Thanks!
Matthew said: short cycling air conditioner problems: Our air conditioning compressor cycles on and of every few seconds or minutes. What can we do to fix this systems not even a year old
(July 17, 2016) Mike said: This was an interesting article. My central AC works perfectly during the night, but short cycles 5 seconds on, half second off on hot days. Any thoughts as to what would be causing this?
2016/09/12 Linda Jackson said: Our Trane Ac unit keeps cycling on and off about every 10 seconds.
(July 19, 2016) Johnny Todd. said: York 3 ton heat pump. Heatpump kick on and right back off? I changed board! Super heat is perfect!! I'm lost plz help! Unit is jumped and and cools great great pressures, but kicks off as soon as it kicks in when wired properly?
(mod) said to Joe and Matthew, Mike, Linda and others (re questions just above):
An air conditioner or heat pump that is cycling off and immediately back on or cycling off/on every 10 seconds is abnormal and is likely to damage the equipment. I would turn the system OFF while waiting for repair, as I worry that more components will be damaged. I suspect this is a control board or relay problem, possibly related to operating temperature or pressure but that's as far as I can get.
Short-cycling on and off of an A/C compressor unit every few minutes (say 1-5 minutes) sounds to me like a diagnosis and repair are needed.
A second sort of "short cycling" of the compressor also suggests that diagnosis and repair are needed: if an air conditioner or heat pump compressor runs for a very long time (i.e. the cooling system is not able to reach the indoor set point on the thermostat) and the the compressor shuts off for just a few minutes, then re-starts, I suspect trouble.
Causes include lost refrigerant, ice-blocked cooling coils, thermostat not working properly (blocked, in sun, in airflow, dust-crud clogged).
But if someone is turning the system on and off quickly, the compressor may have a hard time re-starting against the pressure on its outlet side. A starter capacitor addition or replacement might fix the problem. If your A/C compressor is showing this symptom but works OK if you leave it shut off for 30 minutes or longer, that may be the trouble.
We have also see or a damaged compressor internal refrigerant valve causing high head pressures;
In sum, you need a service call from a professional to correctly diagnose and repair the problem. Ask the service tech what she/he found and let us know - what you find will help other readers.
Overall: I'd like to see a compressor/condenser unit ON cycle time of 10-20 minutes.
The length of time before the next ON cycle of the compressor/condenser unit isn't standard but it ought to be more than 5 minutes, perhaps 10 or more. The rate of heat gain, air leakage and other factors determine how quickly a cooled space heats-up again once the cool air flow stops.
If an A/C or heat pump compressor/condenser unit is on about half-time and is cycling on/off say 3 times in an hour in hot weather while cooling a residential building with typical insulation, air leakage rate, and heat gain rates for its climate, that's probably normal.
In very hot weather an air conditioner or heat pump system may run continuously or nearly continuously as long as the indoor thermostat is calling for cooling.
It's possible for a residential air conditioning system to be operating normally when a compressor shuts off, then turns back on depending on the system's controls. That's so if the "off" period is long - perhaps 10-15 minutes depending on weather conditions and system capacity. In moderate heat, 10 minutes on and 10 minutes off would not be abnormal but in my OPINION it's close to the edge.
A compressor motor that is cycling on and off rapidly is going to be damaged by that condition and depending on the system design, it may also ultimately have trouble re-starting against high head pressure in the system. I think most HVAC techs (more expert than I) will agree that if we get down to 5 minutes or less on and off there is definitely a serious operating problem to be found and fixed.
In any event, 5 Minute on-off cycling or more rapid on-off cycling of an air conditioner or heat pump is very likely an indicator of trouble.
The article above suggests common explanations for on-off or short-cycling of an A/C compressor unit. Usually I think first of an overheating motor. That in turn can be due to a motor that's failing or to another cause such as low voltage; a bad control board or contactor are less-likely candidates but then your onsite tech may find something else.
If your air conditioner or heat pump has the opposite problem, staying on too long, see LONG-ON CYCLING AC COMPRESSOR.
Below you will find questions and answers previously posted on this page at its page bottom reader comment box.
On 2020-09-15 by Anonymous
thank you sir, weird thing happened that same night during hot day cool cycle only ran 7 minutes, but when it cooled off later that evening, the outside and inside units ran for hours even though temp was made inside.
On 2020-09-13 - by (mod) -
Daniel
Check your room or control thermostat; if the AC unit is shutting off because the SET temperature on the thermostat has been reached, that's normal and OK;
If it has not gotten close to the set temperature then the compressor/condenser may be overheating.
On 2020-09-13 by Daniel
In soutb tx have thermostat set to 70, outside unit runs for 7 minutes then shuys off for 20 minutes is that ok?
On 2020-08-13 by Ben
My AC outside unit runs fine during the daytime, but it begins to short-cycle (in less than 1 min) at night time or when the outside air is cooler for the past week or so. I cleaned the condenser and evaporator coils already, air filter is clean as well. Any advice thank you!
On 2020-07-1 - by (mod) -
Aaton
It is normal for an air handler to continue to run briefly at the end of an on cycle in heating mode. It's most common when the system is being used in as it's desirable to purge heat from the heat exchanger, avoiding the risk of damage to the equipment. They may be some systems the do the same thing at the end of a cooling cycle.
On 2020-07-13 by Aaron
After my unit shuts off the air handler continuea to run for a minute. Is that normal?
On 2020-07-04 - by (mod) - very short on-cycles
If you're really seeing very short on-cycles then I agree it's worth further troubleshooting. Perhaps a polite conversation with the HVAC service company's service manager will get you a tech experienced with the issue. Sometimes it's a dirty expansion valve or other control that misbehaves intermittently and of course behaves perfectly when the repair person is on site.
On 2020-07-04 by Dave
We have a one year old Lennox 2 stage A/C. We noticed suddenly that it began short cycling... running for maybe 3 seconds and shutting off, then doing the same thing about 5 minutes later, and again running just a couple of seconds. The temperature inside though was OK, at 75 degrees which was the thermostat setting.
The next day, it worked fine without short cycling. The day after that, it began short cycling again. A HVAC technician came the next day, when it was working fine, and he found nothing wrong. He surmised maybe the low stage is so quiet it was running continually, or something, that didn't make sense. It's started short cycling again, and this time the temp went up to 77. Then it started working again. It's very frustrating as it seems we might be damaging this one year old unit.
On 2020-06-28 - by (mod) -
Christine
Some AC systems include safety controls that will shut the system off to prevent more-costly damage from, for example, overheated components or excessive refrigerant pressure.
So I suspect your system, when it's working hardest, has a component that's overheating or otherwise causing a condition that shuts the system down.
An experienced A/C service tech can track down the failing part.
Keep me posted.
On 2020-06-28 by Christine
A/C turns off during the hottest part of the day for two+ hours.
On 2020-06-15 - by (mod) -
Teresa,
With no more data I can but guess thst the short cycling compressor is due to one of the causes in the article above, perhaps a bad expansion valve
On 2020-06-15 by Teresa
My air conditioner seems to be short cycling. Yet it has a thermostat which has a automatic compressor protection delay to avoid potential damage to the system. At least that’s what the thermostat manual says . So why would it be short cycling ?
On 2020-05-22 - by (mod) -
If not one of the causes above on this page, perhaps a bad relay, control, or even a loose ir bad electrical connection.
On 2020-05-22 by fred
heat pump compressor turns off randomly but fan keeps running
On 2019-07-14 by (mod) - My electric bill is increasing 30-40 every month.
Perhaps an expert electrician onsite making amps checks can find the problem. Watch out, there may be safety or shock hazards.
On 2019-07-12 by Susie
My electric bill is increasing 30-40 every month. Has tapered off after four months. New home. New a/c. Six other new homes, same size or larger, with more people, thermostat set much lower with electric bill 40 or more dollars less. Ac company cannot find anything. Electric company said my cooling percentage is too high.
On 2019-06-11 by (mod) -
A reasonable place to start some guesses about the cause of symptoms you describe would be to go through the list on the page above
Please give that a try and let us know what you think.
On 2019-06-10 by Jim O'Dell
Notice several times lately when outside my Puron Central AC makes a 1 second false start. Kicks on & immediately back off?
On 2019-05-28 by Darren Watson
Why would my condenser stop and start repeatedly before then running continuously when my air handler is running?
On 2019-05-18 by (mod) -
Do you think that replacing the burn to terminal actually corrected the problem that caused the burn up? I can't tell from the text. You might want to go through this with Justin's for short cycling given in the article above on this page.
On 2019-05-17 by Richard D.
(May 17, 2019) Last year at the end of the summer my AC unit burnt the T-1 wire off the top of the Contactor. I didn't repair it until this year. I replaced the terminal end and started it up and now it's short cycling. I will run about 30-45 seconds then shut off for about 1 or 2 seconds then immediately start again an repeat the symptom. Any thoughts on this would be greatly appreciated.
On 2019-02-23 by Hailemariam
The burner cut off in less than a minute .Only blower runs to cycle the air
On 2018-12-08 by (mod) -
probably one of the reasons given in the article above.
Watch the temperature dial in the fan limit control switch as the furnace goes through a cycle and let me know at what temperature the dial is pointing and which direction does it moves when you see the short cycling.
On 2018-12-07 by Gary
What will cause a blower motor to cycle every 30 seconds yet run smooth when the aux heat is used. When the thermostat calls for a 1 or 2 degree rise in temperature the blower motor short cycles but when the thermostat call for 3 degrees or more it doesn't short cycle until the thermostat setting is within 2 degrees. Than the short cycling begins
On 2018-11-15 by (mod) -
Possibly a problem with the defrost cycle.
On 2018-11-14 by Terry
What will make your fan on a heat pump cut on and off
On 2018-08-30 by (mod) -
Joe
On the chance that the burning odor is from an electrical or motor or HVAC equipment failure there is risk of a fire. Sorry to say you should turn the equipment off at its circuit breaker or fuse, then call for repair.
On 2018-08-30 by Joe
Ive been noticing the smell of something burning the past 3 days now it's hot as hell in here. I went outside to see if the unit was running and noticed the unit only runs 5 minutes then it stops.
...
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