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I have a Lennox 13ACD series unit (model 048) and the fan will not start. I can kick start it and it gets up to speed just fine. My best guess from reading online is that it is the capacitor. The values label on the capacitor reads:

50-10pF +/- 10% 440VAC 50/60Hz

Searching online, I am having difficulty finding the exact same capacitor values. I see search results like "45+5 440v" or "50/5 440v" that seem to be shorter descriptions. In what appears to be a suggested replacement using my model number in a google search, I see "60+10.0pF +/-6%" on the label (picture included) in what is said to be a suggested replacement part.

How critical is it that I match the exact capacitor values?

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Ensuring that the voltage rating is sufficient is critical. Any new capacitor should be rated for at least your working voltage.

Matching the capacitance is highly desired.

Note that the two numbers at the start describe the capacitance of two separate capacitors. One capacitor is 50 pF, while the other is 10 pF. Also note that it is rated to have a range of +/-10%, so one capacitor should be within 45-55 pF while the other should be 9-11 pF.

But, these capacitance are much much smaller than what is generally used (by about a million times). The units should be in micofarads (μF), not picofarads (pF).

I don't know exactly how tolerant your motor would be, but the 60/10 is likely close enough (it may be up to 64 uF). It is expected by the manufacturer that you will be able to provide an exact match. This 30% above the nominal 50 uF. My guess is that it'll work, but the motor will be less efficient.

Another solution, if you cannot find an exact duplicate, is to combine two capacitors together. Two capacitors in parallel will add (a 20μF in parallel to a 30 μF would make a 50 μF capacitor). Two capacitors in series will end up being the inverse of the sum of the inverses of their capacitances (two 100 μF in series would make a 50 μF).

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  • Yes, it was a tual run cap, one for compressor, one for starting the fan. Replaced by repair company. I got him go purchase a 2nd for me as a backup (I can definitely replace myself next time) – Roger Aug 1 '16 at 22:50
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Are you sure that is "pf" and not microfarads?

The symbol for micro is a Greek letter mu with a descending tail in the "μ". It could be confused for a "p" fairly easily if the printing is faint. A picofarad rated capacitor would be too small for a motor capacitor and is normally used in very low power electronics circuits.

Here is what I found when I searched your numbers: https://www.amazon.com/Motor-Dual-Capacitor-Round-12892/dp/B00C0YSBTG

The double numbers are because it is a start/run capacitor so it has a dual value. One for start one for run. Check the dimensions on it and see if it matches up. If so then give it a try.

Good luck!

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  • knew is was a 'μ', just did not know how to type that. I thought 'p' was shorthand or something. Thanks – Roger Aug 1 '16 at 22:50
  • p is short for pico (10^-12). μ is micro (10^-6) – Pigrew Aug 3 '16 at 15:02

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