OK, the Facom 04P series are AC electrolytic devices - that is to say rather like two electrolytic caps back to back. As such they are not rated for continuous duty, but they are very small compared to a conventional (polyester or polypropylene ) of the same capacitance. They have a loss factor of nearly  10% so can get very hot if mains is applied  for too long, and are intended for starter circuuits with a pull in time lasting a few seconds, with plenty of cool down in between.
(a Facom data sheet that does not mention any of the nos on that model I presume they have withdrawn it.)

So generally, a higher voltage rated cap will last longer,  and be bigger, but if you can afford the space go for it.

Start caps like this must be used in a circuit where they are de-energised after a few seconds.  Run caps can take continuous duty, so if it fits, you can fit a run cap in place of  a start but not vice versa.

A run capacitor has a more generous rating and size and price to match

example (cornell dubilier are first tier makers so their data is good. so is the cost.) Note how life depends on temperature and voltage - not all makers are this honest, but the physics is similar.

 A start cap is smaller, lower temp rated and shorter lived (example) note the dreadful power factor and the temperature rating compared to the above. But they are smaller and usually cheaper.

Values of caps  for starter uses are usually OK erring up a bit, but not so much down, so for you not less than 21uF, but OK for 22-27.  But in practice, most real motors will take quite a bit more, so  a nominal 27-30 probably also OK.

Get a 25uf 20% or finer tolerance and you will be fine.

(a bit more cap =  more starter torque is normally OK, too little and it may sit there and buzz unhappily without rotating.)

If you get stuck mouser have stock of most  values  from the common makers and can get it to you quite fast. Beware of their delivery charges though. 

Mike.

Thanks for the reply, I have managed to find one which I think should be a good replacement trying to stick as close to the original as possible. I managed to find a site at the weekend which offered some quite good information and quite informative.

Ive managed to find a 21-25uf 330v, similar sort of size so should fit in the same bracket (although no massively important). The part is for a refrigeration compressor so it should only be on for short periods. The cap for the fan has also failed so it's most likely been over running/over heating and so damaged this and the run cap too.

I've attached an image of the one I think should do it.

I'm not sure whether that first reply sent as nothing is showing on my thread. This is what I found over the weekend which looks like potentially the closest to the original facon one I'm likely to find I think. This was actually on the mouser website.

Craig Wheater said:

I've tried several suppliers but seems they don't want to say what would work as a replacement, you'd think if they're supplying them they'd be able to advise the best option when swapping.

No I wouldn't think that at all - they're experts in stock control and pricing, they're not engineers. The capacitor manufacturer themselves may have application experts - or they may well design them to specs passed to them from equipment suppliers. Even if they do have such staff in house that's going to be several layers of people away from the sales end, and they're unlikely to see it as worth passing a request for one capacitor through the chain - the time spent passing the message on alone would quickly wipe out the profit from the sale.

I'm very wary of taking advice from a sales / distribution company on alternative replacements, they may know what they are talking about, or they may be just trying to make a sale (to be fair, most will be honest and say that they can't guarantee that replacements will work). Of course if it's a company that is also experienced in carrying out repair work, and guarantees its own repairs, that's different, they might well know what works as an alternative. 

Fortunately we have Mike here with a fantastic answer!!!!

Yes I know what you mean with regards to sending it to someone in their technical department etc but I've found even when you speak to one of their tech guys they still seem very reluctant to offer advice. I just find it strange that they sell a product but don't really seem to offer any real guidance. And yes fortunately there are sites like this and people like Mike that can help out with their knowledge, it's very much appreciated.

Lisa Miles 

Odd I had answered this and it has all gone...

OK I;ll try again. The facom 04P type cap you have there is an electrolytic starter capacitor

data - though your  exact type is not shown, I assume discontinued.

- think of it as two electrolytic back to back . It is not suited to continuous duty as the loss tangent /power factor is awful (~ 10% typical) so they heat up and go bang if they are not allowed to cool between starts.
But they are smaller and lighter than a 'normal' capacitor of the same rating. A run capacitor is designed for continuous use, so if it fits physically and is the right value,  you can use  a run capacitor as a start but not the other way about.

In general a slightly larger start cap does no harm just a bit more torque on pull-in, say 25uf in place of 20, but  too small and there is a risk  the motor will sit and buzz but not spin.

Compare

motorstart data 

note poor power factor, low running temp, short life

with the data for a good motor run/ 100% duty device 

motor run data

see how over voltage and temperature shorten life and under running improves it. ( Dubilier are a 1st tier maker and their data is more honest than some, though all capacitors are similar really in those regards) - so getting the higher voltage one than the minimum you need does no harm, and is actually a good idea. - except  it takes up more space, and costs more. (though that saving may be lost in the postage and labour costs).

If you get totally stuck electronics places like mouser have a no of suitable objects. beware postage though, but there are plenty of others.

Hope this helps and I do not need to type again.

Mike,

I'm not sure if your last post was removed by me by accident, I accidentally pressed on verify and then it lit up green. Next minute it's not there. Apologies. Non of my replies have been coming up, not sure if they have to be verified first but for some reason yours are coming up and mine aren't.

OK the PSU2130 2130 A is very similar to the original.

An aside, but do you know why the original failed ? (how it failed may tell you - has the blow out vent blown out ? If so it boiled, perhaps a protracted start )

I'm looking at the 2021 manufacturing year and wondering if something happened or if the original designer was a bit hopeful.  It might fail the same way again if the design is under powered.

Mike.

I'm not 100% certain but my best guess is that the fan motor failed to start and this has caused the compressor to over heat putting more strain on the start and run capacitors as both have failed. I did get the system to run, I just gave the fan a push start and everything else seems to work fine. Although I think it may have been a fluke that the compressor managed to start first time. I don't know exactly how long the fans not been running as it could've been playing up for a while. The facon one isn't blown out but is definitely warped in shape, looks to have gotten very hot. It doesn't give out a reading when tested, the run capacitor does but it's at about half what it should be. My wholesalers keep the other ones on the shelf so they are easy to get hold of, the facon one is the awkward one to source. I have come across these before on the same systems, never had as much trouble sourcing the replacement until recently. I have noticed over the last few years the 330v versions have been hard to source....although I didn't know about the mouser website until this weekend. Because theyve been relatively easy to source I've always swapped them like for like and it's always been fine. My knowledge of capacitors is fairly limited so was abit concerned about swapping it for something that's wasn't the same, hence why I was after some advice.