Need help identifying replacement run capacitor.

TheSteadyRightJuly 8, 2014

Hey folks,

We've had a local HVAC/Plumbing company twice inspect our gas furnace as part of a "complimentary" service we had after they did some plumbing work. On both occasions, each technician has stated the blower capacitor is pretty weak and near failure. Their price for replacement was stupid high, and I knew I could do this myself with some research.

First off, to determine if they're trying to BS us into some unneeded replacement, do capacitors really "weaken"? Or do they just fail? I wasn't present at either visit, just my wife, but I assumed they determined it was operating outside of some acceptable capacitance range.

Secondly, assuming we should replace, I need help pinning down a value to order the correct replacement part. I've attached a photo of the run capacitor. From what I understand, I can get a 440v capacitor instead of the 370v I have now without issue. Need to match 50/60hz, and obviously size to fit in the housing. What I'm getting confused on is the 5uf capacitance rating. I'm seeing all sorts of values for replacement parts, none which simply read 5uf. Most are something like 35uf + 5uf, or 40/5 mfd.

Can you guys clarify exactly what I'm reading here, and what value(s) would work as a suitable replacement?

Thanks for the help!

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That's a motor run capacitor
Run Capacitor, 5 Mfd., 370 Volt
Available in oval or round.
Don't worry so much about the shape, the bracket can be bent or made to fit different.
It may or my not need changing but as a DIY item they are cheap.
(Less than $5)

Here is a link that might be useful: Capacitor on ebay

    Bookmark   July 8, 2014 at 3:23PM
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Two values represent two capacitors in the same container. The bigger capacitor (35uf or 40uf) is the start capacitor. The small capacitor (5uf) is the run capacitor. You only need a run capacitor. You can always go higher in voltage, but not lower.

How old is this furnace? It looks very new from the picture. Capacitors do start to go bad over time and it is a good idea to replace them before they fail. I am suspicious the tech actually measured the cap value. I think he is looking to make money on the "complimentary" service. The tech may be getting a commission on the sale. Nothing in life is free.

    Bookmark   July 8, 2014 at 3:39PM
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Thanks for the clarification and info. Seems I was eyeing up dual capacitors instead of just a single.

The furnace is maybe 10-15 years old I believe. I don't have an exact age as we are only in this house about a year, and we purchased from some folks that flipped the house.

I was also thinking they were just looking for an easy buck... Considering it was a year between when they first told us it was "weak" and worth replacing, until telling us the same thing again (and we've had no problems), would you guys bother replacing now? Or just wait?

Might be worth it to just order the part and keep handy if/when the capacitor goes. I assume that's the first place you'd start.

    Bookmark   July 8, 2014 at 8:26PM
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I have replaced the fan capacitors in my oudoor unit. I got mine at Grainger Supply. I chose the more expensive one made in Mexico rather than one from China. Just my prejudice. It cost about $7. The service rep that found I needed it wanted $100 for one, plus labor. I still use that company but I take the advice of some of their reps with a grain of salt. One has told me twice in the last 5 years that I must replace the fan motor on my indoor air handler immediately because it was about to fail. Not so. Still functioning perfectly and I saved hundreds.

    Bookmark   July 8, 2014 at 8:46PM
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