Common Air Conditioner Capacitor Failure Symptoms

Capacitor Failure Symptoms

are sometime harder to identify without the right tools and expertise. the most common symptom of a bad capacitor is that the motors do not run. This is especially true for the compressor. Fan motors can sometimes run even with a bad capacitor but hidden damage is still happening to the fan motor. Fan motors can also run intermittently with a weak or bad capacitor. There are not always visible signs that a capacitor is bad. But there are times when you will see either a balloon shape on the capacitor or a split and leak. But this is not always visible when a capacitor is bad. It’s best to have an expert check the capacitor. There is a high risk of severe electric shock if a capacitor mishandled. This is not a DIY repair.

Types of Capacitors

Capacitors can be found in several different sizes and shapes. There may be one or multiple capacitors included in your ac with regards to the design. While the most popular capacitors are the types found on circuit boards, the ones most associated with air conditioning will be the bigger capacitors that assist start and run your motors. There are several motors present in an conditioner and heater systems:

  1. Compressor Motor Run Capacitor: Here is the most popular capacitor that fails. Most of the time these are duel capacitors, which means that there are 2 capacitors built into one. A duel capacitor will have three terminals on the top where a single capacitor will simply have two terminals on top.
  2. Outside Fan Motor Run Capacitor: That is the smaller capacitor found with or part of the Compressor Motor Capacitor. It helps start and run the outside fan that blows air through the outside coils.
  3. Indoor Blower Motor Run Capacitor: Similar to the outdoor fan motor capacitor, it is a small, single (two terminals) capacitor that will help start and run the indoor blower motor.
  4. Start Capacitor: Some models include an auxiliary start capacitor that helps jump start the motors. Most are found on the compressor. These are less common.

Why do capacitors go bad

When capacitors go south, they either go out entirely or they decline in strength. The decline is measured in the “capacitance” units called micro farads. When the capacitors are produced, they are labeled with their specifications capacitance and a range +/- from the design capacitance. This range is the allowable operating range, usually labeled in a percentage range, for the capacitor. If the capacitor starts to fail, the capacitance measured will be outside of the labeled range. Sometimes these are difficult to find any symptoms unless you have the proper tools. Warning, there is a risk of severe shock, so do not try this at home.

Diagnosing a bad capacitor

If a capacitor goes out completely, or is severely out of its operating range, it may prevent the motor affiliated with it from running completely. If the compressor motor is not working, then the air conditioner will not cool. If the outside fan is not working the compressor may cause problems and will short cycle or cease working. If the indoor fan stops, you’ll find that there is no air blowing through the vents.

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861 thoughts on “Common Air Conditioner Capacitor Failure Symptoms”

  1. If you have time could you answer this question or point me in the right direction. My indoor blower wasn’t working. I changed the capacitor and it started working again. The old capacitor tested weak. It was late and all I had was a 20 mfd so I put it on fan ram through the night. The next morning I put a 5 mfd on it. It’s been three days now and the same problem has come up again. Do I change the dual run that tests okay or do I look deeper in to possible motor failure with windings going to ground. I’m an electrician not an ac tech but I’ve got some knowledge. It maybe time to call in the professional 🤷🏼‍♂️ Thanks for your help and time.

    1. Motors are rated for a specific MFD capacitor. It is set to match the amplitude and cycle of the power wave of the primary winding but at a delayed frequency so that the peak of the wave off the capacitor is timed so that there are three power peaks in the 360 degree cycle. Any change in the strength and//or MFD will move that third winding so that the timing is off. This creates a power “drag” on the motor instead of a properly timed power “boost”, to use aeronautical terms. The electromagnets are thus off timing and rather than pulling the rotor, they act as a break on the rotor. This deviation in the power cycle thus causes undue wear and tear on the motor and can cause early motor failure. It could be the motor has now failed. But yes, putting anything other than a fully functional correct MFD capacitor on the motor is not recommended.

  2. Hi, I have a central system in my home. Recently I have found that the air flow has been noticeably diminished as though the system iced up. I would then raise the temperature on the thermostat so that the compressor would turn off and after a while the airflow would improve. The airflow is normal only when the thermostat is set so high that the compressor stays off. When I drop the temperature the airflow reduces after 20mins which is I think is too short a time for the unit to ice up?…..any thoughts?

    1. Actually, the icing will depend on two things, the humidity level and the suction pressure. Icing is a sign of either a refrigerant leak or a refrigerant restriction. The compressor creates a low pressure condition (vacuum) on the vapor side of the system. This vacuum pressure is directly correlated to the temperature it creates. If the pressure drops due to a lack or refrigerant, the temperature can drop well below the freezing point of water. Its possible that you could have pressures as low as 10 psig which can be a temperature of -20 to -42 degrees F. At these temperatures, it would take only seconds to start icing up which will have an immediate affect on air flow, getting to a noticeable point within 10-20 minutes.

      Long story short, yes it can. But you have a bigger problem. And that problem is damaging your compressor shortening its life.

  3. Wow… First off, Great responses to questions…. not a lot helpful people left… let alone knowledgeable ones…here to being an endagered species!. So, my question… I had to install an all in one gas pack myself last year, thank god i took those 0 days of HVAC training…..
    (it was getting cold… no hvac companies could schedule me inside of 2 weeks…) So, I bought a Maytag, got it delivered to within 17ft of the deceased unit, and spent 16 hours in HVAC labor… ALl that to clarify… the unit is less than 8 months old…

    Anyway… Im sure you have heard it a thousand times… air flow suddenly dropped, and not cooling well…

    Well, I looked in at the compressor… entirely iced over.( i do mean the compressor).. opened the panel, and a leapord slug decided to “goodbye cruel world” on two of three of what I assume is the run capacitor terminals.. blue and yellow were the murder wires….
    I assume the coils were iced over as well… causing the low volume of not cold air problem inside the house…

    safe guess that the capacitor is dead? (ill dig out the multi-meter later and test.. but will likely replace cap even without testing…)
    probability that my compressor cooked?

    i did video the removal of the deceased from the scene if you are curious…

    1. Actually, being iced over sounds like the compressor is working. The issue is either a restriction in the refrigerant flow, a refrigerant leak, or a issue with air flow (possible bad blower motor).

  4. Hello,
    My ac unit was working fine unit about 4pm then it stopped cooling. I turned it off for about 2 hours. I had someone turn it on inside while I was outside by the fan and it hummed and delayed for about 2 seconds and then the fan started to spin. The compressor sounds like it wants to turn on and clicks but it won’t and is make a humming noise. I looked at the capacitor from the panel with out touching anything and it’s rusted on top where the prongs sit on the actual capacitor not the prongs to the wires. Could my capacitor be bad?
    If so what do I look for in replacing it with a quality new one?
    Thanks in advance

    1. Look for the part warranty. Some have 5 year warranty on the capacitors. This indicates better material components and might last longer.

  5. Hello my inside fan keeps turning on and turning off my compressor outside stays running the entire time fan going on is very frequent but 40 times an hour could this be capacitor

    1. Could be a short in the low voltage wiring that is intermittently breaking and connecting. Could be a bad circuit board. Could be the capacitor. This is where a trained service tech is needed. Until someone can rule out the obvious, you need to test everything that could possibly cause this.

  6. Hi–My outside fan and compressor work just fine when my unit is in AC mode, but neither the fan nor the compressor kick on when the unit is in heat mode, although warm air is coming out of my vents, so the blower in the attic seems to be working. Does that sound like the capacitor to you? Thanks!!!!

    1. It very well could be. Sounds like you are running on the secondary heat (heat strips) since the outside is not running. However, the statement that the unit works fine in AC mode leads me to believe it is more of a control or control wiring issue. I would want to know if the outside unit contactor is pulled in and the pressures on the system. It could be a bad defrost board or a short in the low voltage wiring.

  7. I have a national Ac it was working perfectly then it stopped all of a sudden the indoor unit went OFF and the outside unit stopped working too and whenever I try putting it back ON all I hear is a humming sound and won’t start. Pls what could be the problem?

    1. If you are in heat mode and have a gas furnace, then the hum could be your inducer motor and it’s locked up. If you are in AC mode, the hum could be your blower motor locked up but that would not prohibit the outside unit from starting. I need some more info: What mode is the unit in? What type of pieces of equipment is it? Heat Pump? Furnace with split AC?

  8. I have an Armstrong heat pump that comes on, blows cold air but the volume of air is almost non existent through the vents in the floor. Is this a capacitor or possibly a fan motor blower issue?

    1. Since there is little air blowing, it will depend on the mode or the type of blower motor. If you are in AC mode, then you could have a frozen coil. If you are in heat mode and a frozen coil is out of the question or if you are in AC mode and the coil is not frozen, then the motor is probably bad. Ad if it is blowing a little it would sound like you might have a variable speed blower where one of the speed steps may be out. There is a lot to digest on this issue. You really should have a technician come take a look.

  9. Question, I have a 2 Stage 5 Ton Bryant outdoor unit. The fan is only running on the low fan speed, when it tries to engage to high spped we hear a electrical humming/buzzing sound. the home is cooling though. i wounder if this particular unit has 2 capacitors and 1 is shot.

    thank you

    1. There is a capacitor for the Condensing fan, the compressor, and if you have a single speed blower fan. Any variable speed blower is run by a control module and does not require a capacitor.

  10. So the capacitor failed on my unit. I replaced the capacitor and the fan kickstarted and it has been working for a few weeks now. It would seem that it has just failed again with the same issue. Would be it the motor that needs replacing that would possibly take out a brand new capacitor or do I have another issue.

    1. It could be that you just bought a cheap capacitor. Some have longer lives based on the materials in them.

  11. I have an older York unit which is undersized for the house. On AC when it comes on the airflow coming out of the vents is pretty good but after an hour or so running the airflow is very low. What could be the issue? I do not see ice buildup ( on the coils) or any other obstructions.

    1. Could be a dying blower motor. Getting hot and the bearings seizing. Or a bad variable speed control going out.

  12. Hi sir, my name is amandeep today I check 1 ac.when I opened then terminal box the compressor capacitor splitting and the compressor not working then i changed new capacitor 60+5uf. somany times when I start the compressor then compressor working on 2 mins then heat up and then again not working.then I release the gas and flushing machine then same again problem…

    Sir can u tell me what is fault

    1. First I would have to know if 60/5 is the correct size for your compressor. Secondly, you could be low on refrigerant. Third you could have bad bearings in your compressor. I really hope you are not releasing the refrigerant gas. Not sure what you mean by flushing. I would say you need to call a technician.

  13. New therm classic made in 05-2014 made in Mexico had installed 8/1/2016 it work for two week and the inside froze up and they had to replace the coal after that on start up the unit outside Run for A minute or two shuts down then starts back up Run for a few seconds shut down good on Freon The company that installed it so don’t worry it guarantee Keep calling Game back out at your for five times and said that it needed A thermostat they said they would install one heading heard from them installed myself New one and it still doing the same thing what should I do what’s the matter with the unit ? P.s new unit going on a year now not fixed !

    1. Serious diagnostics require someone to use test equipment and cannot be diagnosed over the internet. I need data from my instruments to see what might be happening. I can only guess. Keep trying the installer, he really should be the one to fix it under his own personal warranty.

  14. When my system calls for cold air, the thermostat relay clicks and the blower comes on just for a second, stops for a split-second, then it clicks again and the blower and compressor kicks on and everything starts working fine. So essentially I get 2 relay clicks before they AC is up and running. Oddly, I get two relay clicks when the system is done with the cooling cycle and shutting down. Only happens with the AC and I just replaced the control board. It’s a 4 year old Lennox ML193UH. Thoughts? Thanks in advance.

  15. My ac cools fine but when it first starts the outside unit makes a loud buzzing noise like a bugszapper . It does it about every ten seconds for about a second and then it does it about every 20 seconds for a fraction for the next 5 or 10 minutes and then about every 5. Minutes after that it buzzes for about 10 seconds. Fan motor is spinning all the time. Large pipe next. to freon line is sweating and dripping slightly. Rheem 5 ton unit

  16. I have a 2 ton unit. Works fine for heat and cooling. However, when the unit has been used for heat – we live in FL had it on a few days – then today it was 77/78 out. I went to turn it from heat to cooling and the compressor did not start. This was well past the “cooling on” blinking indicator for the delay. I was reminded this happened in the past and we wait a few hours and turned it on again this time from “off” and it worked fine and again starts daily with no issue when on cooling.

    Can the capacitor be an issue?

  17. Outside unit will come on only after breaker is turned off then back on. Then it shuts off after about ten minutes. Thermostat flashes “heat on” then auxiliary heat comes on after a while. Outside unit seems normal while working just won’t work all the time. Replaced the capacitor on the outside of the unit and the contactor last year. Could the capacitor be bad again?

    1. It could be, but I would really need to put some tools onto the equipment to check pressures and voltages to see what is happening.

  18. My 2 ton, 10 SEER Rheem Classic heat pump (approximately 11 years old) is tripping the circuit breaker. The thermostat will call for heat and air handler turns on, but the outdoor unit will not. I will sometimes hear a “click” outside when the unit should have kicked on. I had a technician out earlier this year when it was doing the same thing. He replaced the capacitor and the circuit breaker and it resolved the tripping issue. When I reset the tripped breaker, the unit will turn on. It usually makes it through one or two cycles before tripping the breaker again. On occasion, it gets caught in defrost mode. I turn the system off at the thermostat, wait 10 minutes and turn it back on and it resolves itself until it trips again. I had the defrost board replaced last winter. The capacitor does not visibly appear that it has failed, but I have not tested it with a multimeter. I do not observe any loose or burnt out wiring. Any thoughts? Thanks.

    1. The breaker will trip in overload conditions. This is when the unit tries to draw too many amps. Typically this is when it starts up and is a sign the motors are going bad. If the motor bearings are worn, then it draws a lot of current to try to get the motor to rotate, thus tripping the breaker. In this case the compressor may be going bad.

      Another reason breakers trip is because of short circuits. That can be a bad capacitor, loose wire, bad heat strips, or other situation where wires may be crossed.

  19. My LG neoplasma split will only run for about 10 seconds before the outdoor unit stops working. The indoor unit continues working but the fan icon on the electronic display disappears and the outdoor unit stops working. after about 1 minute, the fan icon on the indoor unit comes on and the outdoor unit runs again for about 10 seconds before shutting off. this is repeated over and over again. There is no cooling effect and no water coming out of the drainage pipe. When I disconnect the powerline to the outdoor system, the indoor unit tends to work properly with the fan icon on and the fan blowing for as longs as the system is on. Hope that I don’t have a big problem on my hands?

    1. It sounds like you have a serious problem but the information is not enough to provide you with any kind of valid diagnosis. You had better call a professional to put some test equipment on the unit to find the problem.

  20. I have an old carrier heatpump with a Positive Temperature Coefficient Resistor start circuit (like made with a ceramic case) that was replaced with a supco super boost spp6 ptc years ago. Now it is hard to start the compressor again. Should I replace this hard start capacitor with a 3 wire version (ie 521) or would the torque be too much for an old heat pump (over 35 years old)?

  21. have a walk-in cooler that needs to be about 35F. The compressor everything seems to be ok until unit runs for about 30 minutes. the amps get a little high(rla is 10.6, unit slowly as txv opens/closes, increases up to about 14/15amps) then all of a sudden it acts like it is trying to stat all over again and the amps spike up to 40+.(trips breaker) Let it cool some and the time lessens but same issue. Could it be the run capacitor. I checked it originally and it was 20.1 for a 20 microfarad part. I changed the start capacitor as it was reading way high(145-174, reading mid 190’s). The box is starting out warm at 70/72F. Can a run capacitor appear fine but fail under load causing this issue? My mind says yes. Thanks!

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