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capacitors - maintenance?

should the capacitors in a 20 yr old residential AC system be replaced? or wait for them to fail if that ever happens?

not sure freon has ever been added to system and it seems that cooling is not as robust as it should be when its hotter  -  hopefully the prof ac maintenance guy will properly evaluate freon status without being too ambituous with other recommendations for an older system.


  • Brp814
    Brp814 Member Posts: 22
    edited June 2014

    Have you checked the mfd value with a meter? If not check them,and if they are not within a + or - 5% then change them. I find when I am doing maintenance on systems that older run caps hold up a lot better than the newer run caps. Check them first though.
  • elfie
    elfie Member Posts: 264
    older copper pipes

    older copper pipes were better on older systems (dont leak as much a newer systems), valves, etc were all of better quality

    and now capacitors may be better

    those older systems, while energy hogs, can be alot better

    my concern is a person tinkering with the older system while taking a look at system.

    i have been told to just leave systems alone  - the less human contact the better.

    (but i do want to evaluate freon status which may have had some leakage over 20 yrs)

    i say this because the compressor shuts down due to overheating when its humid and hot and maybe this means the freon is low and resulting diminished lubrication may be straining compressor; and air handler keeps going and tends to warm up the place because compressor is off
  • Techman
    Techman Member Posts: 2,144

    elfie, I agree w/ you. This is not a profession for those kind of people. Those TINKERERS give guys like me a harder time to make a living. Now, I do routine/preventative maintenance which involves checking EVERYTHING ,EVERY PART, including capacitors. There has to be a reason why the comp trips off and finding that reason is just part of the job. When was the last time the AC was  washed? W/O taking the unit apart and investigating its kinda hard to figure out whats wrong. So let someone have a look. Now ,I'm not saying that some of the people in this profession are not TINKERERS , there are a few. So stick with whomever shows up and watch. Don't be afraid to say "put that garden hose down and slowly back away from the cond unit, you TINKERer you! "
  • elfie
    elfie Member Posts: 264
    cond shut off

    the coils are clean so this should be the problem

    when there is less humidity when its hotter, the unit stays on for hours without shutting down

    but when it gets humid (and i guess the load increases), it tends to shut down (ie. due to a thermo sensor).

    the unit does sit in the sun and has a metal exterior that is hot to the touch when in the sun.

    i am hoping the freon is on the low side and maybe when adjusted will better lube the compressor during operation
  • earl burnermann
    earl burnermann Member Posts: 126
    Interesting capaitor test

    Here is a formula I found on another site. Lets you check the uf of a capacitor while it is running:

    Read voltage from c to herm on the capacitor.

    Read amps on start lead

    (2652 x amps) /voltage = capacitance under load

    2652 is the constant for 60 hz.

    Haven't tried it yet but the others on the site claim it works.
    If the women don't find you handsome, they should at least find you handy!
  • NYplumber
    NYplumber Member Posts: 503
    Works some times

    Funny you wrote this, I was about to start a thread about this. The formula works sometimes. I use it on caps to see if they fall within the allowable percent written on the cap spec label.

    This week I tested a capacitor and decided it was bad. The replacement capacitor had worse readings! made me think, is the old one bad?!

    On a mother maintenance this week I found a capacitor that was feeding only 30vac between the fan and c terminal. Figured it was bad, replaced it and the new capacitor only had 50 volts between the two terminals. Go figure.... Somethings wrong but I don't know where to start first.

    If anyone has a good article or pdf file to share on capacitors, please share it here. I as well as the rest of us are always looking to learn more.
  • don_9
    don_9 Member Posts: 395
    old unit

    Cleaning an old unit that has never been done could come back to haunt you. I have pulled many of blowers and motors and have clean them up and in some cases had to go back weeks later bc the blower motor went bad.Yep clean the thing up and it grab the air better and pull higher amps due to the new load it has not seen in some time and it could not handle the new 

    All system old or new deserve to be clean and save the customer money in the long run but, you have to make the customer aware of the possibilities.

    I have understanding customer that know the difference when they get air down to the other end of the house that they have never felt before. If the motor goes they understand bc schooling the customer and every way possible make life much easier when you were just there two weeks ago.
  • Techman
    Techman Member Posts: 2,144
    Compressor tripping off

    W/O human contact , when was the cond coil last washed? w/O human contact its hard to make a decision as to why the comp is shutting down on hot days.I'll bet the comp is not working so good on an almost hot day also. You need press/temp readings to help make a proper decision as to whats wrong. Bring in a human to do that.
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