Short on-off cycling of air conditioner or heat pump compressor/condenser unit diagnosis: What causes the A/C or heat pump fan condenser unit to keep cycling on and off rapidly and how do we fix it? Here we explain the common causes of compressor unit short cycling. 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. 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. 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

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.amana wall unit heater ac manual York 3 ton heat pump. stealing copper from ac unitsHeatpump kick on and right back off? furnace blower motor life expectancySuper 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. Continue reading at COMPRESSOR / CONDENSER DIAGNOSTICS or select a topic from the More Reading links or topic ARTICLE INDEX shown below. Or see REPAIR GUIDES A/C / HEAT PUMPIn commercial applications, one of the most important tasks in keeping components running at their peak performance is determining what’s a cause and what’s a symptom if mechanical problems arise. The difference between knowing and not knowing could be thousands of dollars worth of diagnosis. In particular, short cycling seems to be one of those refrigeration and HVAC terms that gets murkier the deeper you get into the water.

This blog post will explain what short cycling is, why it’s harmful for your system, and what issues it is born from. First thing’s first: what is short cycling? Short cycling occurs in your compressor when a mechanical failure is causing the run times to terminate prematurely and since set point has not been achieved, it restarts shortly afterward, thus requiring more compressor ‘ON’ time to compensate. Short cycling is a symptom of a potentially wide range of causes. Think of short 2-5 minute bursts of ON and OFF times that can go on for days, weeks and months before the condition is noticed. Figure 1: NRM Remote Site Manager (RSM) graph of actual customer's system. Shows freezer with severe short cycling due to loss of refrigerant. Because short cycling is usually a sign of a larger issue, it’s important that a technician is able to uncover the root cause as opposed to simply replacing parts or repairing components. These are band-aid fixes and while they may buy you some extended life on your cooling system, it still leaves open the potential for a complete system failure.

“Any time a compressor has failed, a technician needs to find the root cause and correct it before the replacement compressor fails as well. This is not always an easy task, but it is an important part of the service provided to a customer. Having the replacement compressor fail due to an unresolved system issue is not good for the technician, his company, or the customer.1” “If a compressor fails prematurely (<15 years old), first consider why the unit died in the first place. Don’t simply replace the compressor, override a safety and/or apply a band-aid just to get it running again. Odds are, the failure will occur again, perhaps with worse consequences, and surely with wasted expense.2” In addition to repair costs, any compressor that is short cycling will consume a great deal more energy and the controlled space rarely reaches set point. Operating in this condition can consume 20-50% more energy a hidden cost that is rarely linked to the problem. Figure 2: RSM Graph of actual customer.

Shows cooler with short cycling due to tripped evaporator circuit. So now that we know what short cycling is and why it’s important to undertake a thorough diagnosis if it occurs, here are the most common causes (look out for these!): Low refrigerant/oil mixture: Every time a compressor cycles, a small amount of oil that is supposed to keep it lubricated actually travels as a mixture with the refrigerant throughout the system. “If the compressor is cycled off and on too quickly, an imbalance is created. Each time the compressor starts, oil is pumped out, but without sufficient run time the oil stays out in the system and does not return to lubricate the compressor. This imbalance will lead to a shortage of oil inside the compressor and bearing failure1.” Dirty condenser/automatic high pressure reset: With the daily juggling act that business owners face every time they flip the OPEN sign, as long as the compressor is functioning in some capacity, being proactive in the system’s performance or maintenance rarely sees priority status.

A dirty condenser can severely limit your system’s ability to reject heat for regulating temperatures and pressures needed for cooling which can lead to compressor tripping on high head pressure. If the condenser has automatic high pressure reset it can result in short run cycles. High Condenser discharge pressure due to air recirculating: If the condenser is in a confined area where the air used to cool the condenser is recirculated the temperature and pressure will rise causing high pressure reset and short cycling. Usually observed when a condenser is in a basement or attic area and the heat from the condenser heats the air and as it is recirculated it overheats the condenser causing a high pressure trip and reset. Figure 3: RSM graph of actual customer. Shows cooler with short cycling due to condenser fan failure. Pressure or temperature control differential is too small: When the pressure controller’s low pressure differential is set too tight, it can cause the compressor to short cycle.

This can be observed during normal cooling when the low pressure setting is reached and the compressor cycles off until the pressure in the evaporator rises above the high side of the low pressure setting. This results in longer times to achieve set point and greater energy use. Lack of operation time delay: While it’s certainly important to have a minimum and maximum run time in place for proper system performance, it’s equally important to have a minimum OFF time in the form of an operation time delay. This is arguably the most common cause of a short cycle. By having an effective time delay, you can potentially prevent other causes from infiltrating your system. For example, a proper time delay can keep the system from running due to discharged air still circulating in the system immediately after its operation. Another: it can allow the pressure controller to reset itself naturally while not calling for cooling as opposed to firing another cycle based on high pressure triggers due to compromised condensers.

Figure 4: RSM Graph of actual customer. Shows cooler short cycling due to stuck open solenoid valve. Here is a small handful of other causes: compressor valve leaking, no load capacity controls, low airflow, excessive refrigerant, discharge pressure too high. Although it doesn’t have to be, early detection that your compressor is short cycling can be as difficult as figuring out what is the root cause. Now with the advent of IoT (Internet of Things), identifying your compressor is short cycling is possible through real time monitoring, control and data analysis. And given the cost of saved energy and potential product or inventory loss, these solutions have extremely cost effective and a must have. We hope this blog post was informative in helping you troubleshoot a common issue in sub-optimally performing commercial refrigeration systems. Remember, it’s not enough to have a technician replace a malfunctioning part – the root cause of a short cycle must be determined and addressed to avoid future and potentially more serious problems.

National Resource Management implements state-of-the-art controls and automation solutions, with a unique focus on commercial and industrial refrigeration. For over twenty years, NRM’s optimization and analysis tools have been producing long-term energy, maintenance, and operations benefits in tens of thousands of retail coolers, distribution and manufacturing plants, laboratory environmental rooms, and foodservice facilities across North America. NRM’s total end-to-end ownership of the energy analysis, turn-key system design and implementation, and delivery of customer outcomes and support have made NRM the premier refrigeration specialist for utility programs, regulatory agencies, ESCOs, and energy efficiency contractors nationwide. Call us today at 1-800-377-5439 to learn how we can help improve energy and operational efficiency for your cooling system. 1. Ice Breaker: Compressor Short Cycling. 2. Compressors Fail at Mild Temperatures. Preventative Maintenance Techniques for HVAC/R Service Technicians.