Short on-off cycling of air conditioner or heat pump compressor/condenser unit questions & answers:

FAQs help diagnose the causes the A/C or heat pump fan condenser unit that keeps cycling on and off rapidly

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.

Air Conditioner or Heat Pump Short Cycling Diagnostic FAQs

These questions & answers about why an outdoor compressor/condenser unit is turning itself on and off too frequently were posted originally at SHORT CYCLING AC COMPRESSOR - topic home.

Smell of something burning at my air conditioner

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. On 2018-08-30 2 by Joe -

Illustration: the capacity cycling model for a Copeland Scroll digital compressor discussed by Emerson and cited below. [

Reply by (mod)

Joe

Watch out: 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.

 

You can save repair cost by deciding to leave off the anti-short-cycling control - a safety device ?

The anti short cycling device shorted out on the outside air conditioning unit. The service tech wired around it and said I didn’t need to replace it if I didn’t want to spend the money. Question: Do you think it needs to be replaced? He said some of these units are made without one. On 2018-08-20 by Martha

Reply by (mod) -

Martha

I am not smarter than your on-site technician, but I speculate that she's saying you can save repair cost by deciding to leave off a safety device designed to protect the compressor from damage that can be caused due to other problems that show up as short-cycling.

Whose judgement do we prefer: the original installer, the manufacturer (if the short cycling device was part of the original equipment), or the tech who's saving you money?

If the compressor unit is over-sized it will cool adequately but won't run long enough to dehumidify.

I recently had a 3 1/2 T Payne Dual HeatPump/AC installed in Dec 2017. Heat worked perfectly. However in early July the compressor went bad. The air compressor was replaced with a new one. Since the new compressor has been installed it is cycling 5 minutes on and 20 min off.

The temperature is cooling; however the humidity in the house has varied from 50-58% in 90-100 degree temperatures. Service tech checked unit for 2 hrs. He stated since the compressor was cooling everything was ok. I don't agree with him and I don't think he knows how to fix it. This unit is still under warranty. Actually only used 6 months. - On 2018-07-20 by Lilian

Reply by (mod) -

Lillian

If the compressor unit is over-sized it will cool adequately but won't run long enough to dehumidify.

 

On 2018-07-10 by Todd

Hello, i have an older 2.5 ton split heat pump in a So Cal dessert area. Condo is 1200 sq ft and well insulated being built w block and 50% of condo is somewhat sub terrainian. The unit cools adequately yet only has 6-8 degrees diff between hi and low lines.

My question is: after 5-6 hours of operation holding 76f indoors w 109f ambient temps. The inside temp all of a sudden begins to rise as if the system has shut off. I keep the air handler on all the time just for circulation.

Once I realize the AC is not working, I turn off the AC at the thermostat, wait 1-2 minutes, turn it back on and it immediately goes right back to holding the 76f set point for the rest of the day.

I have the condo in escrow and need to have a tech out to service the unit. Any idea what may be causing this every 5-6 hours or what can I tell him to check if he doesn't know?

Thank you so much !

On 2018-07-05 by Hipe

My ac unit was charged several weeks ago. It worked fine until it got extremely hot now the condenser fan is kicking on and off every few seconds. would a overcharged system cause this

On 2018-07-05 1 by (mod) - If only the fan is turning on and off and not the compressor motor

Hipe

If only the fan is turning on and off and not the compressor motor itself then I suspect it is a problem with the fan relay or control.

However if the entire unit is switching on and off it is possible that debris or frosting in the thermostatic expansion valve that meters refrigerant is causing the valve to stick which in turn on some compressor systems will shut off the compressor in response to high-pressure.

On 2018-06-30 by Todd Jacobs - AC blows very cold but outside unity is short cycling

My ac is blowing cold very cold but in a cooling cycle the outside unit will turn on for 5 min or so and then turn off and on immediatly for another 6 minor so then off then on again is this a short cycle but its cooling the home

On 2018-06-30 by (mod) - I think I have a short-cycling heat pump.

Sounds like it to me

On 2018-06-24 by tim

I think I have a short-cycling heat pump. It is essentially new (new build 1600 sq. ft. home 6 months ago).

It is a 30,000btu (2.5 Ton heil system) Since we went into the cooling season we have had nothing but problems with it, from not running to fan only operation, to not removing humidity sufficiently. The installer was confused as to what the problem was so finally a rep got involved. (low amp draw, low pressure were some of the things I heard being talked about)

The only actual things they have done is: replaced capacitor, adjusted low pressure and recently another rep decided is was over-charged ( a tech on the phone with him thought it was a bad coil) so they removed refrigerant and then re-installed. The compressor comes on for 6-7 mins then off for 6-7 mins.

This is about 5 of these on/off cycles per hr. The OAT was 90 with 48 % humidity and my set point is 73 with a 64 % humidity level inside the house.Also, when the compressor shuts of the air handler continues to run for 4 more mins which is just blowing moist air into the house and humidity goes up until the next cycle. At night around 11pm with an OAT of 78 the on/off cycle is 5 mins on 8 off.

Personally I am starting to think it is too big of a system for my house as I had it super insulated with R50 in the attic and R13 in the walls.

The builder normally does R30/R11. His HVAC sub seems to have a standard install of 2.5ton systems in all the homes the builder builds.

I see that a 2000 sq. ft. 4 bedroom home he just built has the same system as mine, so I'm thinking if a 2.5 ton is sufficient for a 2000 sq ft home with R30/R11; it's over kill for my R50/R13 1600 sq. ft.. home....Any thoughts?
Thx

On 2018-06-22 by Shantanu Bandyopadhyay

My Hitachi 3 * AC runs normally at 28 degree. No cooling problem. But compressor starts every after 5 minutes. And run 3 minutes. When comp starts then only my computer UPS fails for fraction of second. Causing the computer reboot. APC 600 V UPS. NEW. 4 Sq MM wiring. No voltage fluctuations. Hopeless. Please suggest

On 2018-06-14 by Chris - Compressor cuts on and off every 5 seconds

We have a two and a half ton condenser and when we cut it on the compressor cuts on and off every 5 seconds and not cooling the house we just got to fix where they had a leak in the copper line in the air handler and he recharged it two weeks later it broke down and the compressor kicks on and off every 5 seconds and started not to cool the house what would be a problem can you bypass to make the compressor work and cool?

The fellow that fixed it the leak in the line said that all the oil came out in the air handler upstairs out of the line and made the compressor not work can I bypass that and how

On 2018-06-15 by (mod) -

Chris

YOu cannot bypass the compressor and have cooling, but you can leave the A/C compressor/condenser powered-off while you wait for repair, and during that time you can turn the air handler fan to ON so that you have some continuous air movement.

 

On 2018-05-23 y Rhonda - AC turns off after about 5 minutes

When I turn my a/ c on it turns off in about five minutes.what could be wrong.

On 2018-05-24 by (mod) -

Probably one of the things listed inSHORT CYCLING AC COMPRESSOR, Rhonda. I'm sorry but with not a shred of information about your system I can't make a smarter guess than what we've organized at SHORT CYCLING AC COMPRESSOR.

Please take a look and let me know if any of that is confusing.

D

On 2018-05-10 by Ron Betz

My outdoor heat pump AC will run smoothly for 2 day and then stop. It will restart if I hose it down. Recently had the fan motor changed but no the problem. Help, Thanks.

On 2018-05-11 by (mod) - overheating compressor

Certainly sounds like an overheating compressor. Before condemning the compressor motor I would want to know that the fan is working correctly.

On 2018-05-12 by Ron Betz

I will check it out. I had the fan replaced last year because of the same problem.The home warranty tech that replaced the fan seemed unsure of his trade. Thanks for your reponse and advice.

 

 

 

Copeland Scroll Digital compressor cycling vs. HVACR compressor motor short-cycling on and off

It's possible that the unit is equipped with a digital scroll which is actually used to prevent short cycling by allowing the machine to reduce load significantly. The scroll is opening and closing to match the building load rather than shutting off and coming back on. If the unit never sounded like this before it’s likely the circuit has gone low on refrigerant which causes the sound to become louder.

The digital scroll can also be turned off to operate like a regular scroll if the noise is unbearable.

http://www.emersonclimate.com/asia/en-ap/products/compressors/scroll_compressors/commercial/copeland_scroll_digital/about_copeland_scroll_digital/pages/how_copeland_scroll_digital_works.aspx

Thank you, - On 2018-05-08 by markk1pe -

 

On 2018-05-08 by (mod) - Copeland Scroll Digital compressor cycling vs. HVACR compressor motor short-cycling on and off

Thank you for the comment, Mark, that;s interesting, It is not clear why a digital scroll compressor would be cycling on and OFF every few minutes. If I have understood the material correctly, Emerson's article on the operation of the Copeland Scroll Digital compressor that you kindly referred describes capacity cycling but doesn't say that the motor actually turns on and off.

Excerpts:

The Copeland Scroll Digital™ compressor increases HVAC system efficiency by precisely matching compressor output to your heating or cooling needs which saves energy and reduces maintenance costs. Developed in 1993, the first application of this technology was in refrigerated marine containers in 1999. In 2000, the air-conditioning version of this technology was first launched in Asia. Today, over one million pieces of these compressors are working in the field all over the world ...

A cycle time consists of a "Loaded State" time, and an "Unloaded State" time (Figure 2). [shown above]

The duration of these two-time segments determines the capacity modulation of the compressor. For example, in a 20-second cycle time, if the loaded state time is 10 seconds and the unloaded state time is 10 seconds, the compressor modulation is (10 seconds x 100% + 10 seconds x 0%)/ 20 = 50% (Figure 3).

If for the same cycle time, the loaded state time is 15 seconds and the unloaded state time is 5 seconds, the compressor modulation is 75%. The capacity is the time averaged summation of the loaded state and the unloaded state. By varying the loaded state time and the unloaded state time, any capacity between 10% and 100% can be delivered by the compressor.

- source: How Copeland Scroll Digital™ Works, [PDF] Emerson Climate, Website: http://www.emersonclimate.com/, retrieved 2018.05/08, original source http://www.emersonclimate.com/asia/en-ap/products/compressors/scroll_compressors/commercial/copeland_scroll_digital/about_copeland_scroll_digital/pages/how_copeland_scroll_digital_works.aspx

Illustrated above illustrates cycling the capacity of an Emerson Copeland Scroll Digital™ HVACR compressor motor:

Live link added 2024/07/26 REFRIGERATION - CONTROLLING DIGITAL SCROLL [PDF] - orignial source https://www.copeland.com/documents/refrigeration-controlling-digital-scroll-technical-information-en-gb-4214506.pdf

Excerpt:

Refrigeration applications such as retail and convenience stores are requesting more and more a system able to cope with varying load fluctuations especially with regard to efficiency, as energy costs continue to rise as a direct subsequence to environmental awareness.

 

On 2018-05-04 by Jeff - AC compressor shuts off then re-starts every few minutes

Tks for the good troubleshooting.
My unit is able to cool continuously (compressor running, air handler blowing..etc) until the setpoint has been reached (say from 83F -> 78F).

However, once it reaches setpoint, then about 2 mins later it kick start the A/C for a few mintes, shuts-off, and then start for another few min... shuts off.. as if oscillating around the setpoint temperature.

Since it's able to bring temp down to 78F so I figure it's not low refrigerant or frozen coil as suggested in this article. It almost seems to be the thermostat is "too sensitive" trying to control on the littlest temperature deviation from setpoint.

This is a new Sensi Wifi Smart thermostat installed in Summer of 2017.
Any thoughts?

On 2018-05-04 by (mod) - AC compressor shuts off then re-starts every few minutes

If the problem began only after you install the new thermostat, and began immediately after you installed it, one would suspect an incompatibility or a wiring error.

On 2018-02-25 by Rog - causes of short cycling compressors

My unit want stay on no more than 10 seconds before cutting off then back on again

On 2018-02-25 by (mod)

Rog

The article SHORT CYCLING AC COMPRESSOR lists common causes of the problem you describe. Most likely that's not something a homeowner can fix; you're likely to need help from a trained HVAC technician.

Also see short cycling related to a defrost problem at HEAT PUMP OUTDOOR UNIT DEFROST CYCLE

 

On 2018-01-31 by CG - defrost cycle problems at the outdoor unit

my air condition/heating fan/condenser? outside when I put the heat inside on it stays on for 5 minutes then shuts it turns on again but the fan outside does not turn,,,I have to manually keep turning the unit off then after few minutes back on to get the heat to come on,, Air conditioner in summer works fine

On 2018-01-31 by (mod)

CG

That sounds to me as if the condenser unit is unable to start- possibly a defrost or failed heater or of course it could be some other problem. A heat pump system in most climates also has a backup heat that should run if the outdoor unit cannot (e.g. due to low temperature).

I would call for repair service. Let me know what you're told as that will help other readers.

See HEAT PUMP OUTDOOR UNIT DEFROST CYCLE

 

 

On 2018-01-03 by (mod) -

Ps try.a new air filter

 

 

On 2017-12-30 by Bev S - New A/C Heat Pump shuts off after 5 minut4es

New A/C and heat pump installed, with this cold weather we have just used the heat. It goes on at desired temperature for 5 or a little more minutes. Then it goes off, am thinking it has reached set point. However, it starts short cycling on for 15 seconds off for 20 seconds.

To be honest it happens at night and I fall asleep counting the on and off cycling. Called company that installed unit. They want to charge us to put in a larger return duct. Does that sound right?

On 2018-01-02 by (mod) -

Perhaps I'm missing something but a reasom a need for more return air migjt be connected to short cuclimf wpuld be.am over heated oil.pr gas fires furnace hear exchanger. I. Unxlear how that would cause a het pump outdoor xpreasor condenser unit to short cycle.

What explanation was offered?

On 2018-01-03 by Bev - taking out a clogged refrigerant filter stopped short cycling compressor

@Bev,
Well I have taken the filter off/out and it does not seem to be short cycling. It is maintaining 78 degrees. Just going on and off every 10-15 minuets to maintain the the temperature.

So my FREE solution is no filter in the return line. This is a totally electric A/C Heat pump unit.

 

On 2017-12-27 by Bam - goodmen heat pump and it keep cutting on and off

I have goodmen heat pump and it keep cutting on and off it comes on for 5sec and back off for 5sec help??

On 2017-12-27 by (mod) -

Bam

The explanations for a heat pump that's short cycling on and off are given in SHORT CYCLING AC COMPRESSOR.

Yes there might be some other snafu that we haven't anticipated. So I'd ask for a service call from your service technician - you don't want the cycling to continue as the equipment is likelyi to be damaged. Turn it off, use backup heat, and call for repair.

 

 

On 2017-08-14 by Morteza - on-off cycling compressor unit traced to bad voltage control relay on unit in Iran

Dear mod, You are right,i opened the system and checked the phase and voltage control with a tester and understood that the incoming power had no problem but the control was faulty and was disconnecting circuit without any reason.

I changed it and now everything is ok.

Thank you Man,best wishes for you from Iran

On 2017-08-14 by (mod)

Great news Morteza. It is so satisfying when you can sort out a problem like a short cycling AC compressor. Thanks for taking the time to give us the feedback.

Daniel

 

 

On 2017-08-13 by Anonymous - At end of my ropes with my a/c.

At end of my ropes with my a/c. Personally, I'm beginning to think it's thermostat wiring related. This is Florida. (86 degrees set at 79) I have a Rudd 14 seer, 1 1/2 year old, 2 1/2 ton system (1235 sq. Ft).

Pressures good, Space gaurd filter (now Merv 11 from Merv 13 in case too restrictive ). . I have R-30 insulation . But the house is almost 100% full sun all day. Ducts fine. Both at move in when changing out thermostat (2002) and with instillation of new A/C (2016) they had difficulty getting the unit to run because the wiring is a little bit different then normal I guess due to this heat pump system.

So I never felt comfortable with the way he wired it to begin with especially not with this new system install (took 2 days for them to figure this out). I do have a picture of the wiring if anyone wants it. So the problem came where on this new A/C install, he took my Honeywell thermostat and he reset some settings, because at first when he could not get the system running, he thought it was the thermostat even after I told him that it was the wiring due to my experience 15 years ago when I first moved in here and we had put this thermostat in.

However the guy didn't listen so after trying a new thermostat and realizing it wasn't the thermostat he finally played with the thermostat settings and realized it was the wiring. So I didn't even know those settings existed until I did some research yesterday because, my AC kilowatts has only dropped approximately 1 to 200 a month. I don't get it because we're talking about a 30 year old AC replacement versus a brand new 14 SEER AC.

And I noticed it seems to be running non stop... It was running for 30 minutes and shutting off for 15 minutes . Yes it's cool and humidity less Tha 50% and maintaining steady temps as my shown both on the thermostat AND on 2nd mini temp / humidity gauge I bought to compare. Both exact same.

However, it had never run this long in all the years I've lived here. And same Kilowatts each from from previous years (same temps/days ....) just doesn't seem right. So I found the installer directions and it seems to me some of the functions of the thermostat was not set correctly, in fact I know it wasn't.

When I look at the wiring, that also does not look correct..... in fact my emergency Heating wire is absent altogether. So tells me I only have heat pump and no longer emergency heat if I should ever need it. After changing the settings on the thermostat now it's Cycles on for 6 to 9 minutes and stays off for 15 to 20 minutes still maintaining a steady temperature.

Humidity still in the house about 50% (90 % outside ). My concern is even though it doesn't come back on in quick cycles (stays off for at least 15 minutes), most of the time it's only coming on for 6 to 9 minutes tops. I read that it should stay on for 10 to 15 minutes. So I either go with the setting that makes it run Non-Stop for 30 minutes shutting down for 15 min or cycling on every 15 to 20 minutes and only staying on for 6 to 9 minutes. (Same temps /humidity)

I don't know what's right and what's wrong, all I know is the results with two different thermostats, are the exact same. Please don't ask me is the thermostat set to the appropriate setting because reality is I'm not sure it's wired right to begin with.

And so now like I said I can send someone a picture of How It's wired and they can tell me if I've got it wired wrong. Yes I know I can call someone but there are a bunch if idiots out there that don't get it which is why I'm trying myself to figure it out. No one I've called checked any of that. They say oh it's working. Really ? Clue- longer run times same freaking electric bills. Slight decrease only. Not right

On 2017-08-13 by Anonymous

At end of my ropes with my a/c. Personally, I'm beginning to think it's thermostat wiring related. This is Florida. I have a Rudd 14 seer 1 1/2 year old, 2'1/2 ton system (1235 sq. Ft). Pressures good, Space gaurd filter (now Merv 11 from Merv 13 in case too restrictive ).

I have R-30 instillation. But almost 100% full sun all day. Ducts fine. Both on move in and new A/C they had difficulty getting the unit to run because the wiring is a little bit different then normal I guess due to this heat pump system. So I never felt comfortable with the way he wired it to begin with. I do have a picture if anybody wants it.

So the problem came where he took my Honeywell thermostat and he reset some settings because at first when he was installing he thought it was that I kept telling him it was the wiring due to my experience 15 years ago when I first moved in here and we had we put this thermostat in. However the guy didn't listen so after trying a new thermostat and realizing it wasn't the thermostat he finally played with the thermostat settings and realized it was the wiring.

However, my AC kilowatts have only dropped approximately 1 to 200 a month. I don't get it because we're talking about a 30 year old AC in a brand new 14 SEER AC. It was running for 30 minutes and shutting off for 15 minutes . Yes it's the cool and humidity less Tha 50% and maintsinging steady temps as my shown on 2nd mini temp gauge I bought to see.

However, it had never run this long in all the years I've lived here. And same Kilowatts just doesn't seem right. So I found the installer directions and it seems to me some of the functions of the thermostat was not set correctly in fact I know it wasn't. When I look at the wiring that also does not look correct in fact my emergency Heating wire is absent altogether. So tells me I only have heat pump and no longer emergency heat if I should ever need it.

After changing the settings on the thermostat now it's Cycles on for 6 to 9 minutes and stays off for 15 to 20 minutes still maintaining a steady temperature. Humidity still in the house about 50% (90 % outside ). My concern is even though it doesn't come back on in quick Cycles and stays off for at least 15 minutes most of the time it's only coming on for 6 to 9 minutes tops. I read that it should stay on for 10 to 15 minutes. So I either go with the setting that makes it run Non-Stop for 30 minutes shutting down for 15 or cycling on every 15 to 20 minutes and only staying on for 6 to 9 minutes.

I don't know what's right and what's wrong all I know is the result scenes in the rooms of the two different thermostats to be the exact same. Please don't ask me is the thermostat set to the appropriate setting because reality is I'm not sure it's wired right to begin with. And so now like I said I can send someone a picture of How It's wired and they can tell me if I've got it wired wrong.

 

On 2017-08-11 by Morteza - running cycle takes around 6 min but after around 2 minutes its compressor stops for 2 second and then restart again

My AC system works but there is a problem.Its running cycle takes around 6 min but after around 2 minutes its compressor stops for 2 second and then restart again,in each cycle this happens 2 or 3 times!

On 2017-08-11 (mod) -

Morteza, at we discuss some causes of A/C system short-cycling, as you might have read. beyond those causes, from just your brief question I don't know of a more-specific suggestion I could make other than to ask for advice from your service tech.

In my OPINION a system that is cycling on and off every few minutes and bouncing on and off every 2 seconds needs repair, perhaps just to a control or relay, and I add that while waiting for the service technician, I'd leave the system off to reduce the chances of more costly damage.

 

 

 

On 2017-01-29 2 by Steven hagewood - What keeps a heat pump from kicking on

What keeps a heat pump from kicking on

On 2017-01-29 by (mod) - What keeps a heat pump from kicking on

• Check first for power at the unit
• Then check the thermostat settings
• Then check the control boards/relays
  
  even a loose wire or corroded space connector can be at fault or there can be a more costly issue like a failed compressor motor

On 2017-07-04 by Anonymous - cleaning fixed the control

I cleaned it and it works fine now

 

On 2016-12-06 by Katy king - should compressor be running when on heat setting?

With central heat and air unit, should compressor be running when on heat setting?

On 2016-12-09 by (mod) - Yes if the system is a heat pump

Katy

If your system is a heat pump then if the outdoor air is not too cold for it to operate the heat pump compressor will run in heat mode

 

 

On 2016-11-24 by James - compressor gets hot and recycles

Compressor get hot n recycling quick

On 2016-11-24 by Anonymous Compressor get hot n recycling quick

James,

I agree that short cycling compressor could be due to one of the causes listed in SHORT CYCLING AC COMPRESSOR. There could also be simply a problem with a failing control.

But when the compressor motor is getting hot, I suspect also problems like a failing compressor motor, low voltage, or similar operating problem.

 

On 2016-09-13 by Deborah Campbell My outside a/c unit will cut on and run for awhile, then I'll hear it cycle through and shut off.

Having the same problem as Wesley:

My outside a/c unit will cut on and run for awhile, then I'll hear it cycle through and shut off. When I check the thermostat it is reading 75 with the air temp set on 71, the inside is still running while the outside unit is off. Then the outside unit comes back on and runs for awhile again but shuts off after some time. You can feel the air coming from the vents and it feels cold but still stays hot in the house. Any ideas as to why the outside unit keeps shutting off

Anyideas. Both inside and oitaidw units are less than a year old.

On 2016-09-15 by (mod) - My outside a/c unit will cut on and run for awhile, then I'll hear it cycle through and shut off.

Thanks Steve. More likely it's the drain that gets clogged but indeed a float switch can foul up and stop working. Typically it gets replaced.

Deborah:

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. IN any event, 5 Minute on-off cycling is very likely an indicator of trouble.

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.

At REFRIGERANT FLOODBACK, LIQUID SLUGGING we explain how liquid refrigerant entering a heat pump or air conditioner compressor motor can destroy it and we discuss the recommended time that the system should be LEFT OFF if was switched off while it was running

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.

But 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).

Another cause of short cycling is an over-sized A/C compressor. The unit cools down the interior space too quickly. One result is that it doesn't dehumidify adequately due to those short "on" cycles.

SHORT CYCLING AC COMPRESSOR 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.

On 2016-09-15 by steve

The float switch on the condensate drain line can get plugged with debris and need a blow out. or vaccuum.

 

On 2016-07-19 by Johnny Todd.

York 3 ton heatpump. Heatpump kick on and right back off?? I changed board!! Super head 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???, plz help

Question: broken wire

(Mar 7, 2014) Anonymous said:

The manual thermostat for my A/C and Heat had a wire break into and I replaced the thermostat with a Lux programable one. Do I need to do anything to the new thermostat other than reattach the wires to the correct screw terminal?

Reply:

Nope. You sould be fine.

See THERMOSTATS, HEATING / COOLING where we discuss wiring.

Question: Lennox spilt system heat pump not working

Lennox 2.5 split system heatpump condenser fan not working in heat or cool with "o" thermostat. ices completely over. over summer the outside unit made an awful noise at startup and compressor often cycled twice right after startup. emergency heat works. fan seemed to be turning slowly last time it ran at all.

Reply:

Check out the diagnosticvs beginning at DIAGNOSTIC GUIDE A/C or HEAT PUMP

Question: what can cause a new a/c unit to short cycle?

(July 25, 2015) kevin said:
what can cause a new a/c unit to short cycle?

(Sept 3, 2015) Short Cycle said:
We had a Day/Night 410 A unit that was short cycling. Found no freon leak evidence. Changed capacitor because it was weak. Still no good. Noticed contactor not staying engaged when quick disconnect was pulled out. Changed thermostat. This eliminated problem. Unit runs fine.

Reply:

Short

Your comment will assist other readers; thanks. Are you saying that the problem was the thermostat? Sounds odd, more like a loose wire or a bad control or relay ("contactor")

Question: AC shortcycling

(Jan 27, 2016) Wiz said:
Question: Question: What would cause the contactor to stay engaged for a few minutes then disengage and engage rapidly? This makes a noise like the fan is falling apart and happens whether it is on Heat or Cool.

(May 25, 2016) Wesley said:
My outside a/c unit will cut on and run for awhile, then I'll hear it cycle through and shut off. When I check the thermostat it is reading 75 with the air temp set on 71, the inside is still running while the outside unit is off. Then the outside unit comes back on and runs for awhile again but shuts off after some time. You can feel the air coming from the vents and it feels cold but still stays hot in the house. Any ideas as to why the outside unit keeps shutting off

(May 31, 2016) Annie said:
My AC shortcycles about very 10 seconds. Repaiman thinks the unit is too big for the house. But going to a smaller unit will require some new duct work. Does this make sense? Have already fixed coils, repaired a leak and changed thermostat

Deborah Campbell said:
Having the same problem as Wesley:
My outside a/c unit will cut on and run for awhile, then I'll hear it cycle through and shut off. When I check the thermostat it is reading 75 with the air temp set on 71, the inside is still running while the outside unit is off. Then the outside unit comes back on and runs for awhile again but shuts off after some time. You can feel the air coming from the vents and it feels cold but still stays hot in the house. Any ideas as to why the outside unit keeps shutting off

(July 19, 2016) Johnny Todd. said:
York 3 ton heatpump. Heatpump kick on and right back off?? I changed board!! Super head 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???, plz help

Reply:

Annie,

I'm not smarter than your on-site AC guy but 10 seconds sounds awfully fast for evenb for an oversized AC system problem. Perhaps there is a control, sensor, or relay issue.

Question: Ac runs for about 15 minutes sometimes 20 no matter what

(July 2, 2016) Julia said:
Having problem Ac runs for about 15 minutes sometimes 20 no matter if I have it at 76..78..ect..stops for about 3 to 6 minutes then starts up again with no change in inside temperature..mind you it about 100+ outside sometimes 89 it does not matter it does the same thing landlord has had Ac service person out twice only to tell me nothing is wrong...well my electric bill says different! Any advise?

Reply:

Please see our updated replies at SHORT CYCLING AC COMPRESSOR

What about a compressor that stays on too long instead of too short a time?

If your air conditioner or heat pump has the opposite problem, staying on too long, see LONG-ON CYCLING AC COMPRESSOR.

...

Continue reading at SHORT CYCLING AC COMPRESSOR or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• COMPRESSOR / CONDENSER DIAGNOSTICS
• AIR CONDITIONING & HEAT PUMP SYSTEMS

Suggested citation for this web page

SHORT CYCLING AC COMPRESSOR FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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