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Old 08-27-2014, 10:40 PM   #1
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40mfd vs 45mfd capacitor?


Old capacitor was 45mfd and was replaced with a 40mfd. The unit runs now but will this still work long term? Why would the service provider use the 40 to begin with? Thanks!

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Old 08-27-2014, 11:09 PM   #2
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40mfd vs 45mfd capacitor?


That's probably the closest he had on the truck. Hard to say if it will have any negative effects.

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Old 08-27-2014, 11:11 PM   #3
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40mfd vs 45mfd capacitor?


it'll work, the motor it's attached to which required an original 45 will now run a tad bit slower.

mostly techs will use a plus/minus 5 if they do not have the correct one on the truck. he should have put the 40 on and told you it will work until he comes back with the exact 45 replacement.

not a huge deal, but not right nonetheless.
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Old 08-27-2014, 11:52 PM   #4
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40mfd vs 45mfd capacitor?


Sad things is I waited 4 days for him to order it and the part to come in? And he put 45mfd on the invoice.
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Old 08-28-2014, 12:39 AM   #5
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40mfd vs 45mfd capacitor?


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Originally Posted by Edj1919 View Post
Old capacitor was 45mfd and was replaced with a 40mfd. The unit runs now but will this still work long term? Why would the service provider use the 40 to begin with? Thanks!
It will not hurt it. As long as it runs fine and the capacitor is not showing any signs of stress (bulging, very hot to the touch), I would not worry about it.

The manufacturers have a lot of tolerance built into their units, to allow for some variance in parts like the capacitors. You just do not want to go too large or too small of a mfd on the part.
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Old 08-28-2014, 07:15 AM   #6
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40mfd vs 45mfd capacitor?


I have a different opinion than gregzoll. Todays manufacturer's engineer systems close tolerance. Example, wires just long enough to reach the terminals, sheet metal casings thin, just enough screws to hold panels on, etc,etc. If the unit came with 45MFD it was engineered for 45MFD. Yeah, you can get away with a lot of non oem parts but it will catch up some where , sometime when you least expect it. Another thing to think of is. Suppose the owner sells the property and the new owner calls a PRO to repair it he finds the 40 MFD cap bad and has a 35 on the truck and thinks O it's only 5 under. BAM now you have a unit that is 10 under. Imagine equipment that is 20/30 years old? One of the first things I always do is ask the owner when has the equipment been worked on last just to find out what the guy before me did.
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Old 08-28-2014, 07:24 AM   #7
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40mfd vs 45mfd capacitor?


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Suppose the owner sells the property and the new owner calls a PRO to repair it he finds the 40 MFD cap bad and has a 35 on the truck and thinks O it's only 5 under. BAM now you have a unit that is 10 under. Imagine equipment that is 20/30 years old? One of the first things I always do is ask the owner when has the equipment been worked on last just to find out what the guy before me did.
Very good point..
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Old 08-28-2014, 11:48 AM   #8
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40mfd vs 45mfd capacitor?


The tolerance on most capacitors is at least +/- 5%
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Old 08-28-2014, 01:56 PM   #9
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40mfd vs 45mfd capacitor?


Using a 40 in place of a 45 for a weekend is okay. But not as a permanent replacement.
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Old 08-28-2014, 01:59 PM   #10
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40mfd vs 45mfd capacitor?


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The tolerance on most capacitors is at least +/- 5%
Some even more then that.

That is the manufacturers manufacturing tolerance. Meaning that a new 45uF at 5% could be as low as 42.75. And the OPs new 40 at 5% could be as low as 38. So would you want a 38uF capacitor running your expensive to replace compressor that should have a 45.

Ed. Go to Graingers and get a 45uf.
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Old 08-28-2014, 04:07 PM   #11
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40mfd vs 45mfd capacitor?


beenthere: You are correct.I was just stating the facts of the tolerances of caps these days.I do some electronics that take electrolytic caps and some of the tolerances on those are -5% to + 20% on the high end caps.
I was just stating facts from the manufacturers .
His 45mf cap from Grainger still has the same tolerance but will be closer in range with what he's replacing and better for the unit.

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