Which specs matter when replacing a fan capacitor?

Question

I'm trying to repair a 14-year old ceiling fan that runs slow. Capacitors sound like a common problem. What I'm not sure is which replacement capacitor is best.

Here's photos of this fan's capacitor and wiring in its control box.

Using a digital multimeter to test capacitance between the red wire and the gray wire across from it on the capacitor, I got a reading of 0.430uF. I did that test by sticking one multimeter probe-needle into the gray wires' wirenut where it was able to contact their aluminum, and sticking the other probe-needle into the red wire's terminal in the plastic 9-wire connector. Given the capacitor's labor showing gray-to-red should have 3.5uF, I am thinking this supports the idea that the fan runs slow because the capacitor has gone bad. I am new to working with capacitors (done much more electrician than electronics DIY) so I might be reading this wrong, as I understand the capacitor could simply be 'under charged'. I disconnected the fan from its power source 1-2 days ago.

If it does make sense to replace the capacitor, my question is, what to replace it with? I found the two options below and neither is exactly a match - I can't seem to find an exact match.

A. https://www.lowes.com/pd/Harbor-Breeze-Ceiling-Fan-Triple-Capacitor/5012906113

B. https://hqrp.com/hqrp-ceiling-fan-capacitor-cbb61-35uf5uf6uf-5wire-plus-hqrp-coaster.html

Both options have the same number and colors of wires, which is what Lowe's tech support claims is all that matters. Option A from Lowe's has the first voltage at 350V vs the original 300V, and its capacitance is higher at 4.5uF vs 3.5uF and 6uF vs 5uF. Option B from a less reputable dealer is a closer match, with the only difference between 250V vs original 300V on one line. Am I right in thinking option B is the way to go for this replacement, since capacitance should match exactly, and having a slightly lower voltage is not a big deal given it is >240V anyway for this fan which is on a 120V circuit?

Any general feedback about this repair is also welcome. I am wavering on whether to just get a new fan. $12 in replacement parts seems better than $120 in new fan, and I'd like to reduce waste and learn skills when repair is reasonable.

Answer 1

If you're going to attempt to test capacitance, you have to remove the capacitor from the circuit, first. In circuit, you're not testing the capacitor, you're "testing" everything it's connected to. Which tends to invalidate the test results. Since your plan is to replace it, get it out of the circuit and then test it again. If it's still off, maybe you'll have success replacing it with a different one.

Capacitors sound like a common problem.

Or, capacitors are a part people like to throw at motors in the hopes that they will magically fix a problem. Often as not (without actually troubleshooting the problem) it just means more money down the drain and no fix. But sometimes the thrown part happens to be the problem.

For a replacement:

Voltages should be equal to or greater than the original. Hopefully obviously, for an AC rated capacitor you need an AC rated replacement, not a DC replacement (which tend to explode when reverse polarity is applied.) The voltage rating for a motor capacitor frequently needs to be well above the supply voltage.

Capacitance should be the same as the original, though typically tolerances are loose enough that + or - 20% or so is not an issue.

There are much more complete sources for new capacitors than Lowes or "less reputable other supplier," such as actual electronics suppliers. You can also buy 3 separate capacitors (and wire them up correctly) rather than a 3-in-1 if you can't find a 3-in-1 to suit.

To reiterate - test the original one properly, by removing it from the circuit. If it tests pretty much where it should be that way, it's unlikely that a replacement capacitor will do anything but add $12 to the cost of replacing the fan anyway.