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AC Compressor (C) D Friedman AC/ Heat Pump Compressor Short Cycle FAQs
Q&A on Diagnosing A/C or Heat Pump cycling on & off too often

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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.



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Air Conditioner or Heat Pump Short Cycling Diagnosis

Air conditioner compressor (C) Daniel FriedmanThese 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.

On 2017-08-14 by (mod) - how to send a photo for comment

Anon

You can use the page top or bottom CONTACT link to send a photo for comment, or a sketch, but most-likely I'm going to be stuck with having to suggest that we look at the wiring diagrams given in the equipment's cover sticker and in its installation manual. Have you got those?

On 2017-08-14 by (mod) - on-off cycling compressor unit traced to bad voltage control relay

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 2017-08-14 by Morteza

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 2017-08-13 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 (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 2017-08-11 by Morteza

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

I cleaned it and it works fine now

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

On 2017-01-29 2 by Steven hagewood

What keeps a heat pump from kicking on

On 2016-12-09 by (mod) - should compressor be running when on heat setting?

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 2016-12-06 by Katy king

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

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 the article above. 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 2016-11-24 by James

Compressor get hot n recycling quick

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.

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.

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.

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 2016-09-13 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 2016-07-19 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 GUIDES A/C / 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 closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or see COMPRESSOR / CONDENSER DIAGNOSTICS

Or see REPAIR GUIDES A/C / HEAT PUMP

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