Good that you ordered the 440v. That's what your original one was. The manufacturer did that for a reason.
No, that's not really the correct way to look at the topic.
I'll explain this again ... from the beginning ...
Here's how a capacitor is rated; they have several statements on their labels:
- one is capacitance they will store
- one is the tolerance they provide
- one is the max voltage they are rated for
- one is a safety approval (usually, but not always)
- the rest is a part number... etc ... there's always other stuff on the label, but we don't really care about that stuff
CAPACITANCE
this is ths rating of how much energy they will store/release. This is the "micro Farad" rating. When you see a "45/5" capacitor, it is a dual rated unit at 45 mF for the compressor and also has a separate internal circuit for the 5 mF for the fan motor. Or some older systems have seperate capacitors; one 45 for the herm and one 5 for the fan. You always want to get a capcitor that exactly matches the OEM spec.
TOLERANCE
this is right next to the capacitance statement. It will say "+/- 5%", or something like that. That means when operating properly, the actual capcitance will be within 5% of the "rated" value. For example, a 45 mF rating should be no lower than 42.75 and no higher than 47.25, so that it provides close to what the energy requirement is to properly assist the motor. Too little makes the motor stuggle and overheat. Too much burns up the motor windings prematurely.
VOLTAGE
this is the rating of how much voltage they will store/release. They can be either single rated (only 370v or only 440v), or be dual rated (370/440v). As long as the voltage rating is at or above the expected supply voltage, they are fine. This is a max applied allowed volts; it's not a minimum. Capacitors will safely store up to the allowed max rating, but they do NOT increase volts as supplied. Even if you had a 440v rated capacitor, and applied 120v to charge it, it would then "hold" a 120v potential. Because these capacitors can be used in both single phase systems (120/240 volts) and three phase systems (440v), you will see the higher ratings. Capacitors ONLY store the max volts they are presented with. They do NOT create or step up voltage. In the old days, some capacitors were rated for only a 370 application and could not be used for commercial 440v systems. But the industry saw the value of making dual rated capacitors applicable to both, therefore making less parts needed to stock; hence both a cost savings (less inventory on the shelves) and a space savings (less inventory in the truck). Pretty much any capacitor you see today will either be 370/440, or 440. When used in a 240v system, both are perfectly OK. When used in a commercial system at 440v, both are OK. The only thing that would be NOT OK would be using an older single-rated 370v cap in a 440v system, because it's under-rated for the application.
SAFETY APPROVALS
typically decent companies will seek and attain a safety rating such as CE or UL to prove they make a component that is safe for humans and equipment to use.
THE REST
part numbers, production date codes, etc; nothing really the consumer needs to worry about
Snagglefoot had found two choices, a standard unit rated at 370/440 and a HD unit rated at 440. Either would have done the exact same job because he's using them in a 240v system (a typical home system). The HD is an uprated (better) choice becuase it's probably made with thicker films inside and overall a better construction (thicker shell and insulators). Hence the higher cost. EITHER WOULD WORK just the same in his application! It's likely the HD version may last a bit longer because of the HD construction, but that's not an assured garauntee.