After some research, I decided to try to fix an intermittency problem with my AC by replacing the capacitor as a likely yet inexpensive (mistake if not the) cause. The capacitor has three terminals, C(ommon), FAN, and HERM(etically sealed compressor). It is rated as 45 + 5 uf (micro farads), +/- 5%. Here is the old, rusty capacitor (FAN -> purple wire with white terminal, C -> red, HERM -> yellow):

enter image description here

The capacitance measurements between the old and the replacement capacitor are as follows:


C - FAN = 5.01 uf
C - HERM = 44.9 uf


C - FAN = 5.13 uf
C - HERM = 46.3 uf

Is the difference in measurements between the old and the new capacitor substantial and could it be the cause for the intermittency? It looks like the old capacitor measurements are within 5% of the specification but the top was very rusty so I am still hoping it was the issue (and the replacement will fix it).

  • 1
    Have you considered cleaning the terminals?
    – crasic
    Aug 3 at 1:42
  • 2
    The difference in measurements of the old and new capacitors is much too small to cause a problem, especially one of intermittance. In addition, all of the measurements are within the stated tolerance. It is more likely, as suggested by the previous comment, that if the problem is with the capacitor, it is the connections.
    – Barry
    Aug 3 at 1:59
  • As long as the problem doesn't reoccur, I'm happy. We'll see
    – amphibient
    Aug 3 at 2:04
  • @crasic what should I clean them with? Some chemical or just a brush or sand paper?
    – amphibient
    Aug 3 at 2:05

Those values are ok 10% +- from the stated values is normal, a cap going bad can cause intermittent problems one check it can measure ok the next open until it fails. The compressor may be overheating and shitting down if it’s the cap.

The contactor also a possibility could possibly not making contact, give it some time and if the problem returns change the contactor next rust and pitted contacts can cause problems.

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