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Ralph Mowery

In article ,
says...

The hard start cap is only good for momentary contact. It's to be
disconnected as soon as the motor has achieved 'run' rpms. Otherwise,
you'd toast the cap. IE; it sends a surge of current to the start
windings to get the motor up and going, and within a few seconds, a
relay is supposed (in some) to kick it off the start cap/windings and
onto the run cap/run windings.

As I said though, hvac isn't my specialty and I fully admit I could
be wrong in how the cap is being used in this way.

Everyone seems to be dancing around the hard start capacitor.

It allows the motor to draw lots more current for a very short time to
get the motor up to speed faster. As the motor spins up it draws less
and less current. When it is at its rated speed , it will draw less
current .
As most fuses and breakers do not trip at the instant they reach their
marked current, but take some time to heat up and trip depending on how
much over the marked value the current is. By using the hard start kit
the current will be over the marked value by a good ammount, but it will
be short enough not to trip the breaker. Where without the kit it will
take the motor longer to get up to speed and the breaker will trip
during the longer slightly over loaded condition.

Think of it as how long you can hold your hand to a hot surface. You
can touch a very hot object for a very short time and not get burnt.
YOu can touch a cooler object longer before a burn.

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