Higher Capacitor

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  #1  
Old 09-09-08, 07:35 AM
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Higher Capacitor

Hi. Recently I had an A/C company replace the run capacitor
in my condensing unit outside. The Tech replaced the cap with
a 35/7.5 mf. When that cap blew, I noticed that the recommended cap on the side of the fan asked for a 5mfd.
I know that voltage is an issue but as long as it higher I'm ok,
but wouldn't the higher mf cause the unit to run hotter and
blow quicker. Or at least, run the unit below performance?
Thanks.
 
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  #2  
Old 09-09-08, 03:01 PM
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The two numbers separated by a slash mean you have a dual capacitor here. Good service practice calls for "identical" replacement. 7.5mf is "50%" larger than the original 5mf...no good!
Not to say that this oversizing caused the newer capacitor to blow-up but it sure is a possibility. And to answer your question, it sure is possible to strain the motor if put to work together with so grossly an oversized replacement cap.
What are the Mfr. and model number of this condensing unit?
 
  #3  
Old 09-09-08, 04:43 PM
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Agree with pflor.

Replacing a 5 with 7.5 is very bad. You can go up 10% temporarily (some say perminantly) to get a unit up and running, but need to obtain the correct cap asap.

But, this "fudge factor" is really applicable to larger caps. I've never seen a 5.5 Mfd cap. I would, in a heartbeat use a 50Mfd in place of a 45 Mfd. That cap would work fine.

However since I can't be sure that a voltage spike won't kill that cap next year and the next tech doesn't notice it takes a 45 Mfd, and he doesn't have a 50 Mfd but does have a 55 Mfd (10 %) rule again, now we would be 20% over.

So, as said, I will always return with the correct cap.

Line voltage is 10% up or down.

For caps you can change a 370 volt cap with a 440 but not a 440 with a 370.
 
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Old 09-09-08, 06:43 PM
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Originally Posted by Jarredsdad View Post
Agree with pflor.

Replacing a 5 with 7.5 is very bad. You can go up 10% temporarily (some say perminantly) to get a unit up and running, but need to obtain the correct cap asap.

But, this "fudge factor" is really applicable to larger caps. I've never seen a 5.5 Mfd cap. I would, in a heartbeat use a 50Mfd in place of a 45 Mfd. That cap would work fine.

However since I can't be sure that a voltage spike won't kill that cap next year and the next tech doesn't notice it takes a 45 Mfd, and he doesn't have a 50 Mfd but does have a 55 Mfd (10 %) rule again, now we would be 20% over.

So, as said, I will always return with the correct cap.

Line voltage is 10% up or down.

For caps you can change a 370 volt cap with a 440 but not a 440 with a 370.

A motor that requires a 7.5 mfd capacitor will not work with a 4.0 mfd capacitor. Much the same way, a motor will not run properly with a weak capacitor. This is not to imply bigger is better, because a capacitor that is too large can cause energy consumption to rise. In both instances, be it too large or too small, the life of the motor will be shortened due to overheated motor windings. Motor manufacturers spend many hours testing motor and capacitor combinations to arrive at the most efficient combination.

There is a maximum of +10% tolerance in microfarad rating on replacement start capacitors, but exact run capacitors must be replaced. Voltage rating must always be the same or greater than original capacitor whether it is a start or run capacitor. Always consult manufacturers to verify correct capacitor size for the particular application.

Cheers!
 
  #5  
Old 09-09-08, 07:34 PM
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Finally caught you!

Here is a link that Real deal may have plagrized from:
http://dnr.louisiana.gov/sec/execdiv...p/hvac/d/d.htm

I unfortunately can not find a link to referance that supports my view that I don't have to pay for. Because a lot of things I referance and look at when answering posts are from TEXT BOOKS.

As stated earlier, pflor is correct the replacement of a 5Mfd with a 7.5 Mfd is very incorrect.
 
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Old 09-09-08, 07:53 PM
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Originally Posted by Jarredsdad View Post
Here is a link that Real deal may have plagrized from:
http://dnr.louisiana.gov/sec/execdiv...p/hvac/d/d.htm

I unfortunately can not find a link to referance that supports my view that I don't have to pay for. Because a lot of things I referance and look at when answering posts are from TEXT BOOKS.

As stated earlier, pflor is correct the replacement of a 5Mfd with a 7.5 Mfd is very incorrect.
I am simply putting up what is available for anyone to read. I think it answered the question perfectly and no need for me to give lengthy answers to simple problems (which I of course could). You said that as if I often do such things. I in fact have never done it prior to this post. It was simply to save time.

Cheers!
 
  #7  
Old 09-11-08, 08:06 PM
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Originally Posted by The Real Deal View Post
I am simply putting up what is available for anyone to read. I think it answered the question perfectly and no need for me to give lengthy answers to simple problems (which I of course could). You said that as if I often do such things. I in fact have never done it prior to this post. It was simply to save time.

Cheers!
Putting up to me means posting a link. Not copy pasting stuff and having it look like your own wisdom.

Originally Posted by The Real Deal View Post
(which I of course could)
I doubt you can.

Here is a link on the subject, not the one I was looking for - wish I had saved it. But the writer apparently read the same BOOK I did.

http://www.achrnews.com/Articles/Fea...00f932a8c0____
 

Last edited by Jarredsdad; 09-11-08 at 08:09 PM. Reason: fixed quote
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