Capacitor sizing if unknown

[BigJon3475]

How would you go about finding the proper size of a capacitor for a split system heat pump if it was "lost". Obviously you would just match if you knew what was used from the factory. Let's say 2 ton system. I don't have a specific application but this was brought up in another forum and no one seemed to know how to "properly" size the capacitor. You guy's would be the one's to ask if anyone. Thanks In Advance.

If I need to provide more specific info let me know I can grab some figures. I'm just trying to get an idea about how the size is figured.

[old gas bottle]

there may be away to work it out on run amps,but obviousley the best way is to track the info down or take a guess and sit there with your clamp meter,not ideal but if needs must.

[BigJon3475]

You mean start off with a known cap that is smaller and use your amp probe....The keep upsizing till you get the lowest amp draw possible.....I have heard after this though you must drop down one size or 1/2 uf after finding the lowest amp draw.

Meaning if the lowest amp draw was a 5 uf then drop back to a 4.5 uf and be done with it....

I was curious as to if there was a formula or not I'm decent with electricity..not to the engineering side of it but if it could be explain in simpler terms besides going into the engineering I was curious if it was possible.

[Brian_UK]

Just done a Google on this one and surprise, surprise - there isn't a formulae for this.

There are obviously some things that can't be worked out by the humble tech.

[momo]

I like the trial method using reduced amperage, from fan problems, I've tried it, also watching the rpm, and ducting load.

However I once posted a solution - subject to testing - feed back welcome:
http://www.refrigeration-engineer.co...wreply&p=59070

[BigJon3475]

http://tpub.com/neets/book2/3.htm

Found this in another thread... may help some. Use the next button I think there is like 10 pages.